Class 8

Haryana State Board HBSE 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती InText Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती InText Questions

सोचिए, चर्चा कीजिए और लिखिए (पृष्ठ 64)

प्रश्न 1.
अरशद के पास एक चतुर्भुज ABCD की पाँच माप हैं। ये माप AB = 5 cm, ∠A = 50°, AC = 4 cm, BD = 5 cm और AD = 6 cm हैं। क्या वह इन मापों से एक अद्वितीय चतुर्भुज बना सकता है? अपने उत्तर के कारण दीजिए।
उत्तर:
दिए गए आँकड़ों से वह चतुर्भुज ABCD नहीं बमा सकता है, क्योंकि दिए गए प्रश्न में चतुर्भुज ABCD के बिन्दु C को निर्धारित करने के लिए कोई भी मान नहीं दिया गया है।

पृष्ठ 66

प्रश्न (i).
हमने देखा कि एक चतुर्भुज को पाँच मापों से एक अद्वितीय चतुर्भुज की रचना की जा सकती है। क्या आप सोचते हैं कि चतुर्भुज की किन्हीं पाँच मापों से ऐसी रचना की जा सकती है?
उत्तर:
एक चतुर्भुज के बनाने के लिए निम्नलिखित में से किन्हीं पाँच मापों का होना आवश्यक है-
(i) जब चार भुजाएँ और एक विकर्ण दिया हुआ हो।
(ii) जब दो विकर्ण और तीन भुजाएँ दी गई हो।
(iii) जब दो आसन्न भुजाएँ और तीन कोण दिए गए
(iv) जब तीन भुजाएँ और इनके बीच के दो कोण दिए गए हों।
(v) जब अन्य विशिष्ट गुण जात हों।

प्रश्न (ii).
क्या आप एक समान्तर चतुर्भुज BATS की रचना कर सकते हैं, जिसमें BA = 5 cm, AT = 6 cm और AS = 6.5 cm हों? क्यों?
उत्तर:
दिया है-
BA = 5 cm
AT = 6 cm
AS = 6.5 cm

हम जानते हैं कि समान्तर चतुर्भुज की सम्मुख भुजाएँ बराबर होती हैं,
अत: चतुर्भुज BATS में,
BA = ST = 5 cm.
AT = BS = 6 cm.

रचना-
(i) सर्वप्रथम BA = 5 cm खींचा
(ii) बिन्दु B से 6 cm तथा बिन्दु A से 6.5 cm के चाप लगाये जो बिन्दु S पर काटते हैं।
(iii) बिन्दु से 5 cm तथा बिन्दु A से 6 cm के चाप लगाया, जो बिन्दु T पर काटते हैं।
(iv) B को S से तथा T को S और A से मिलाया। BATS अभीष्ट चतुर्भुज है।

प्रश्न (iii).
क्या आप एक समचतुर्भुज (Rhombus) ZEAL की रचना कर सकते हैं, जिसमें ZE = 3.5 cm, विकर्ण EL = 5cm है? क्यों?
उत्तर:
हम जानते हैं कि समचतुर्भुज की सभी भुजाएँ बराबर होती हैं। अत: चतुर्भुज ZEAL में प्रत्येक भुजा = ZE = 3.5 cm तथा विकर्ण EL = 5 cm.
अत: चतुर्भुज ZEAL की रचना की जा सकती है।

प्रश्न (iv).
एक विद्यार्थी एक चतुर्भुज PLAY की रचना करने का प्रयास करता है, जिसमें PL = 3 cm, LA = 4 cm, AY = 4.5 cm, PY = 2 cm और LY = 6 cm, है, परन्तु वह इसकी रचना नहीं कर सका। कारण बताइए।
[संकेत-एक कच्ची आकृति की सहायता से चर्चा कीजिए।
उत्तर:
यहाँ दिए गए आँकड़ों द्वारा खींची गई रफ आकृति दी गई है। इसके अनुसार,

(iv) , अत: ∆PLY की रचना सम्भव नहीं है। अतः वह रचना नहीं कर पाया।

पृष्ठ 68

प्रश्न 1.
पाठ्यपुस्तक की पृष्ठ-संख्या 68 पर दिए गए उदाहरण-2 में क्या हम पहले AABD खींचकर उसके बाद चतुर्थ बिन्दु C को ज्ञात करके चतुर्भुज की रचना कर सकते हैं?
उत्तर:
हम जानते हैं कि त्रिभुज की रचना के लिए त्रिभुज की तीन मापों का होना आवश्यक है, लेकिन प्रश्न में AABD की दो माप AD और BD दी गयी हैं। अत: इस प्रकार चतुर्भुज की रचना नहीं की जा सकती है।

प्रश्न 2.
क्या आप एक चतुर्भुज PQRS की रचना कर सकते हैं, जिसमें PQ = 3 cm, RS = 3 cm, PS = 7.5 cm, PR = 8 cm और SQ = 4 cm हैं? अपने उत्तर की पुष्टि कीजिए।
उत्तर:
दिए गए आंकड़ों के आधार पर चतुर्भुज PQRS की रचना नहीं कर सकते, क्योंकि AQSP नहीं बना सकते, क्योंकि

पृष्ठ 69

प्रश्न 1.
यदि हमें M पर 75° माप के स्थान पर 100° की माप दी गई हो, तो क्या आप पाठ्य-पुस्तक की पृष्ठ संख्या 68 पर दिए गए उदाहरण 3 में बताए गए चतुर्भुज MIST की रचना कर सकते हैं?
उत्तर:
हाँ, M पर 75° की माप के स्थान पर 100° की माप लेकर चतुर्भुज MIST की रचना की जा सकती है।

प्रश्न 2.
क्या आप एक चतुर्भुज PLAN की रचना कर सकते हैं, यदि PL = 6 cm, ∠A = 9.5 cm, ∠P = 75°, ∠L = 150° और ∠A = 140° हैं?
उत्तर:
क्योंकि ∠P = 75°, ∠L = 150° और ∠A = 140°
∠P + ∠L + ∠A = 75° + 150° + 140° = 365°
हम जानते हैं कि चतुर्भुज के चारों कोणों का योग 360° होता है।
अत: चतुर्भुज PLAN की रचना सम्भव नहीं है।

प्रश्न 3.
एक समान्तर चतुर्भुज में दो आसन्न भुजाओं की लम्बाइयाँ दी हुई हैं। क्या हमें रचना करने के लिए अभी भी कोणों की मापों की आवश्यकता है जैसा कि पाठ्य-पुस्तक के उदाहरण-3(पृष्ठ 68) में दिया है?
उत्तर:
प्रश्न में दी गई मापों से समान्तर चतुर्भुज की रचना सम्भव नहीं है। एक अद्वितीय चतुर्भुज प्राप्त करने के लिए चतुर्भुज में पाँच मापों की आवश्यकता होती है, लेकिन इस प्रश्न के अनुसार एक समान्तर चतुर्भुज की केवल दो आसन्न भुजाओं की लम्बाइयाँ दी गई हैं, अत: इस समान्तर चतुर्भुज की रचना करने के लिए कोणों की मापों की आवश्यकता है।

पृष्ठ 71

प्रश्न 1.
पाठ्य-पुस्तक में पृष्ठ संख्या 70 पर दिए गए उदाहरण-4 में हमने सर्वप्रथम BC रेखा खींची। इसके स्थान पर दूसरे अन्य प्रारम्भ बिन्दु और कौन-से हो सकते
उत्तर:
BC खींचने के स्थान पर रेखा AB अथवा रेखा CD से चतुर्भुज की रचना आरम्भ की जा सकती है।

प्रश्न 2.
हमने अभी तक चतुर्भुजों की रचना के लिए कोई पाँच मापों का प्रयोग किया। क्या एक चतुर्भुज की रचना करने के लिए पाँच मापों के अलग-अलग समुच्चय (अभी तक देखी गईं मापों के अतिरिक्त) हो सकते हैं?
निम्नलिखित समस्याएँ प्रश्नों के उत्तर देने में आपकी सहायता कर सकती हैं
(i) चतुर्भुज ABCD जिसमें AB = 5 cm, BC = 5.5 cm, CD = 4 cm, AD = 6 cm और ∠B = 80° हैं।
(ii) चतुर्भुज PQRS, जिसमें PQ = 4.5 cm, ∠P = 70°, ∠Q = 100°, ∠R = 80° और ∠S = 110° हैं।
आप स्वयं कुछ और उदाहरणों की रचना कीजिए और एक चतुर्भुज की रचना के लिए आंकड़ों की पर्याप्तता/ अपर्याप्तता ज्ञात कीजिए।
उत्तर:
(i) दिए गए आँकड़ों से चतुर्भुज की रचना हो सकती है।
(ii) दिए गए आँकड़ों से चतुर्भुज नहीं खींच सकते हैं।

प्रयास कीजिए। (पृष्ठ 72)

प्रश्न 1.
आप एक आयत PQRS की रचना कैसे करेंगे, यदि आप केवल PQ और QR की लम्बाई जानते हैं?
ज्ञात है:
आयत की भुजा PQ तथा QR की लम्बाई हम जानते हैं कि आयत की सम्मुख भुजाएँ बराबर होती हैं,
अत: PQ = SR तथा QR = PS तथा ∠P = ∠Q = ∠R = ∠S = 90°.

रचना-
(i) रेखा PQ खींचा।
(ii) बिन्दु P पर PS लम्बाई का तथा बिन्दु Q पर QR लम्बाई का लम्ब डाला।
(iii) S को P तथा R से तथा R को Q से मिलाया।
(iv) PORS अभीष्ट आयत है।

प्रश्न 2.
एक पतंग EASY की रचना कीजिए, यदि AY = 8 cm, EY = 4 cm और SY = 6 cm हैं (आकृति देखें)। रचना के दौरान आपने पतंग के कौन-से गुणों का प्रयोग किया है?

दिया है-
AY = 8 cm, EY = 4 cm तथा SY = 6 cm.
या AE = EY = 4 cm तथा AS = SY = 6 cm.

AO = OY ………..(i)
AY = AO + OY
⇒ AY= AO + AO […(i) से।]
⇒ AY = 2AO
⇒ 8 = 2AO
⇒ AO = = 4 cm
तथा OY = 4 cm

रचना-
(i) कोई भी उपयुक्त लम्बाई लेकर रेखा PQ खींची।
(ii) PQ पर कोई बिन्दु O लिया।
(iii) O से PQ पर OY = 4 cm तथा OA = 4 cm लम्बाई के लम्ब डाले।
(iv) बिन्दुYसे PQ पर EY = 4cm तथा SY = 6cm का चाप काटा।
(v) Y को E तथा 5 से तथा A को E तथा 5 से मिलाया।
(vi) EASY अभीष्ट पतंग है।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 5 आँकड़ो का प्रबंधन Ex 5.2 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 5 आँकड़ो का प्रबंधन Ex 5.2

प्रश्न 1.
किसी शहर के युवा व्यक्तियों के एक समूह का यह जानने के लिए एक सर्वे किया गया कि वे किस प्रकार का संगीत पसन्द करते हैं । इनसे प्राप्त आंकड़ों को संलग्न पाई चार्ट में दर्शाया गया है । इस पाई चार्ट से अग्नलिखित प्रश्नों के उत्तर दीजिए-

(i) यदि 20 व्यक्ति शास्त्रीय संगीत पसन्द करते हैं, तो कुल कितने युवा व्यक्तियों का सर्वे शास्त्रीय मनोरंजन किया गया था?
(ii) किस प्रकार का संगीत सबसे अधिक व्यक्तियों द्वारा लोक संगीत पसन्द किया जाता है?
(iii) यदि कोई कैसेट कम्पनी 1000 सी.डी. (C.D.) बनाये, तो वह प्रत्येक प्रकार की कितनी सी.डी. बनायेगी?
हल :
शास्त्रीय संगीत पसन्द करते हैं = 20 व्यक्ति,
परन्तु पाई चार्ट में दिया है कि संगीत पसन्दं करते हैं = 10%
माना x युवा व्यक्तियों का सर्वे किया है ।
तब, का 10% = 20
x × \(\frac { 10 }{ 100 }\) = 20
⇒ x = 20 × 100
⇒ \(\frac{20 \times 100}{10}\)
⇒ x = 200
अत: 200 व्यक्ति शास्त्रीय संगीत पसन्द करते हैं।

(ii) सबसे अधिक व्यक्तियों द्वारा मनोरंजन संगीत पसन्द किया जाता है। (40%)

(iii) (a) शास्त्रीय संगीत के लिए सी.डी. = \(\frac{10 \times 1000}{100}\) = 100

(b) लोक संगीत के लिए सी.डी. = \(\frac{30 \times 1000}{100}\) = 300

(c) मनोरंजक संगीत के लिए सी.डी. = \(\frac{40 \times 1000}{100}\) = 400

(d) उपशास्त्रीय संगीत के लिए सी.डी. = \(\frac{20 \times 1000}{100}\) = 200

प्रश्न 2.
360 व्यक्तियों के एक समूह से तीन ऋतुओं- वर्षा, सर्दी और गर्मी में से अपनी मनपसन्द ऋतु के लिए मतदान करने को कहा गया । इनसे प्राप्त आँकड़ों को संलग्न चित्र में दर्शाया गया है-

(i) किस ऋत को सबसे ऋतु अधिक मत मिले ?
(ii) प्रत्येक त्रिज्यखण्ड का केन्द्रीय कोण ज्ञात कीजिए ।
(iii) इस सूचना को दर्शाने के लिए शीत एक पाई चार्ट खींचिए।
हल :
(i) शीत ऋतु को सबसे अधिक मत (150) मिले।

(iii) पाई चार्ट-

प्रश्न 3.
निम्नलिखित सूचना को दर्शाने वाला एक पाई चाट खींचिए। यह सारणी व्यक्तियों के एक समूह द्वारा पसन्द किये जाने वाले रंगों को दर्शाती है-

हल :
प्रत्येक त्रिज्यखण्ड का केन्द्रीय कोण ज्ञात करने की सारणी –

पाई चार्ट-

प्रश्न 4.
संलग्न पाई चार्ट एक विद्यार्थी द्वारा किसी परीक्षा में हिन्दी, अंग्रेजी, गणित, सामाजिक विज्ञान और विज्ञान में प्राप्त किये गये अंकों को दर्शाता है । यदि उस विद्यार्थी द्वारा प्राप्त किए गएं कुल अंक 540 थे, तो निम्नलिखित प्रश्नों के उत्तर दीजिए-

(i) किस विषय में उस विद्यार्थी ने 105 अंक प्राप्त किये?
(संकेत- 540 अंकों के लिए केन्द्रीय कोण 360° है।)
अत: 105 अंकों के लिए केन्द्रीय कोण क्या होगा?
(ii) उस विद्यार्थी ने गणित में हिन्दी से कितने अधिक 9 अंक प्राप्त किए ?
(iii) जाँच कीजिए कि क्या सामाजिक विज्ञान और गणित में प्राप्त किए गए अंकों का योग विज्ञान और हिन्दी में प्राप्त किये गये अंकों के योग से अधिक है।
(संकेत : केवल केन्द्रीय कोणों पर ध्यान दीजिए ।)
हल :

(i) विद्यार्थी ने हिन्दी विषय में 105 अंक प्राप्त किये ।
(ii) गणित में प्राप्तांक = 135
तथा हिन्दी में प्राप्तांक – 105
प्राप्तांकों में अन्तर = 135 – 105 = 30
गणित में हिन्दी से 30 अंक अधिक प्राप्त किये ।

(iii) सामाजिक विज्ञान तथा गणित में प्राप्तांकों का योग = 97.5 + 135 = 232.5 अंक
विज्ञान तथा हिन्दी में प्राप्तांकों का योग = 120 + 105 =225
अंक अत: सामाजिक विज्ञान तथा गणित में प्राप्त किए गए अंकों का योग हिन्दी और विज्ञान में प्राप्त किए गए अंकों के योग से अधिक है।

प्रश्न 5.
किसी छात्रावास में विभिन्न भाषाएँ बोलने वाले विद्यार्थियों की संख्या दी गई है । इन आंकड़ों को एक पाई चार्ट द्वारा प्रतिक

हल:
त्रिज्यखण्ड के केन्द्रीय कोण की सारणी-

पाई चार्ट-

Haryana State Board HBSE 8th Class Maths Solutions Chapter 5 आँकड़ो का प्रबंधन InText Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 5 आँकड़ो का प्रबंधन InText Questions

पृष्ठ 73-74

प्रश्न 1.
एक चित्रालेख (pictograph) –

(i)जुलाई के महीने में कितनी कारों का उत्पादन हुआ ?
(ii)किस महीने में कारों का अधिकतम उत्पादन हुआ?
हल :
(i) जुलाई में 250 कारों का उत्पादन हुआ।
(i) सितम्बर में कारों का अधिकतम उत्पादन 400 हुआ।

प्रश्न 2.
एक-दण्ड आलेख (bar graph) :

(i) इस दंड आलेख द्वारा क्या सूचना दी गई है?
(ii) किस वर्ष में विद्यार्थियों की संख्या में अधिकतम वृद्धि हुई?
(iii) किस वर्ष में विद्यार्थियों की संख्या अधिकतम है?
(iv) बताइए कि यह सत्य है या असत्य : “2005-2006 में विद्यार्थियों की संख्या 2003-04 की संख्या की दुगुनी है।”
हल :
(i) इस दण्ड आलेख में विभिन्न शैक्षिक वर्षों में कक्षा VIII के छात्रों की संख्या दी गई है।
(i)विद्यार्थियों की संख्या में अधिकतम वृद्धि वर्ष 2004-05 में हुई।
(iii)विद्यार्थियों की संख्या अधिकतम शैक्षिक वर्ष 2007-08 में है।
(iv) यह कथन असत्य है।

प्रश्न 3.
द्वि-दण्ड आलेख (double bar graph) : .

(i) इस द्वि-दण्ड आलेख द्वारा क्या सूचना दी गई है?
(ii) किस विषय में विद्यार्थी के प्रदर्शन में सबसे अधिक सुधार हुआ है?
(iii) किस विषय में प्रदर्शन में गिरावट आई है?
(vi) किस विषय में प्रदर्शन समान रहा है?
हल :
(i) वर्ष 2005-05 और 2006-07 में एक विद्यार्थी द्वारा विभिन्न विषयों में प्राप्तांकों की सूचना दण्ड आलेख में दी गई है।
(ii) विद्यार्थी के प्रदर्शन में अधिकतम सुधार गणित में हुआ है।
(iii) अंग्रेजी में प्रदर्शन में गिरावट हुई है।
(iv) हिन्दी में प्रदर्शन एक-सा रहा है।

सोचिए, चर्चा कीजिए और लिखिए। (पृष्ठ 75)

प्रश्न 1.
यदि हम एक-दण्ड आलेख के दण्डों में से किसी एक की स्थिति बदल दें, तो क्या प्रदर्शित जानकारी में कोई बदलाव या परिवर्तन होगा? क्यों?
हल :
नहीं, सूचना में दण्डों की स्थिति बदलने से प्रदर्शित जानकारी में कोई परिवर्तन नहीं बनेगा।

प्रयास कीजिए (पृष्ठ 75)

दी हुई सूचना को निरूपित करने के लिए एक उपयुक्त आलेख खाचिए।

प्रश्न 1.

हल :
दिए गए आँकड़ों का दण्ड आलेख खींचने के लिए X-अक्ष पर महीने और Y-अक्ष पर बेची गई घड़ियों की संख्या को अंकित करेंगे। हमें 6 गणितीय आँकड़े दिए गए है, अत: हम क्षैतिज रेखा पर समान दूरी पर 6 बिन्दु लगाएँगे और इन बिन्दुओं पर समान मोटाई के आयत खींचेंगे।

प्रश्न 2.

हल :
दिए गए आँकड़ों को दण्ड आलेख द्वारा अंकित करने के लिए X-अक्ष पर पसन्द और Y-अक्ष पर बच्चों की संख्या दिखायेंगे। स्कूल A, B और C के पैदल व साइकिल से आनेवाले दोनों बिन्दुओं के आँकड़े दिए गए हैं। अत: क्षैतिज रेखा पर दो बिन्दु लेंगे तथा प्रत्येक बिन्दु पर समान चौड़ाई के तीन आयत खींचेंगे। इनकी ऊँचाई गणितीय आँकड़ों का संगत चित्रानुसार होगी।

प्रश्न 3.
8 सर्वश्रेष्ठ क्रिकेट टीमों द्वारा ODI में जीतने का प्रतिशत:

हल:
X-अक्ष पर टीम और Y-अक्ष पर उनकी जीत का प्रतिशत अंकित करते हैं। चैम्पियन ट्रॉफी से वर्ल्ड कप 2006 तक के प्रतिशत को बिन्दु अंकित रेखा से तथा 2007 में ODI के प्रतिशत को गहरी रेखा से दर्शाते हैं।

पृष्ठ 76

प्रश्न 1.
विद्यार्थियों के एक समूह से यह बताने को कहा गया है कि वे किस पशु को सबसे अधिक घर में पालना पसन्द करेंगे। इसके परिणाम नीचे दिए गए हैं:
कुत्ता, बिल्ली, बिल्ली, मछली, बिल्ली, खरगोश, कुत्ता, बिल्ली, खरगोश, कुत्ता, बिल्ली, कुत्ता, कुत्ता, कुत्ता, बिल्ली, गाय, मछली, खरगोश, कुत्ता, बिल्ली, कुत्ता, बिल्ली, बिल्ली, कुत्ता, खरगोश, बिल्ली, मछली, कुत्ता।

उपर्युक्त के लिए एक बारम्बारता बंटन सारणी बनाइए।
हल :
हम मिलान चिन्ह का प्रयोग करके आँकड़ों को बारम्बारता सारणी में रखेंगे

पृष्ठ 78

प्रश्न 1.
निम्नलिखित बारम्बारता बंटन सारणी का अध्ययन कीजिए और उसके नीचे दिए हुए प्रश्नों के उत्तर दीजिए:

(i) वर्ग-अन्तरालों की माप क्या है?
(ii) किस वर्ग की सबसे अधिक बारम्बारता है?
(iii) किस वर्ग की सबसे कम बारम्बारता है?
(iv) वर्ग-अन्तराल 250-275 की उच्च सीमा क्या है?
(v) किन दो वर्गों की बारम्बारता एक ही है?
हल:
(i) वर्ग-अन्तरालों की माप 25 है।
(ii) वर्ग 200-225 की बारम्बारता सबसे अधिक है।
(iii) वर्ग 300-325 की सबसे कम बारम्बारता है।
(iv) वर्ग-अन्तराल 250-275 की उच्च सीमा 275 है।
(v) वर्ग 150-175 और 225-250 की बारम्बारता एक जैसी है।

प्रश्न 2.
अन्तरालों 30-35, 35-40 इत्यादि का प्रयोग करते हुए एक कक्षा के 20 विद्यार्थियों के भारों (kg में) के निम्नलिखित आँकड़ों के लिए एक बारम्बारता बंटन सारणी बनाइए:
40, 38, 33, 48, 60, 53, 31, 46, 34, 36, 49, 41, 55, 49, 65, 42, 44, 47, 38, 39
हल :
बारम्बारता बंटन निम्नांकित प्रकार से बनेगा :

पृष्ठ 79

प्रश्न 1.
इस आयत चित्र के दण्ड़ों से निम्नलिखित प्रश्नों के उत्तर दीजिए।

(i) कितने अध्यापकों की आयु 45 वर्ष या उससे अधिक है परंतु 50 वर्ष से कम है?
(ii)35 वर्ष से कम आयु वाले अध्यापकों की संख्या कितनी है?
हल :
(i) 5 अध्यापक
(ii) 35 वर्ष से कम आयु वाले अध्यापकों की संख्या = 4 + 5 + 6 = 15

पृष्ठ 80

प्रश्न 1.
आयत चित्र को देखिए और अके नीचे दिए गए प्रश्नों के उत्तर दीजिए:

(i) इस आयत चित्र के द्वारा क्या सूचना दी जा रही है?
(ii) किस वर्ग में अधिकतम लड़कियाँ हैं?
(iii) कितनी लड़कियों की लम्बाई 145 cm या उससे अधिक है?
(iv) यदि हम लड़कियों को निम्नलिखित तीन श्रेणियों में विभाजित करें, तो प्रत्येक श्रेणी में कितनी लड़कियाँ होंगी?
150 cm या उससे अधिक – समूह A
140 cm या उससे अधिक परन्तु 150 cm से कम – समूह B
140 cm से कम – समूह C
हल :
(i) इस आयत चित्र के द्वारा कक्षा VII की लड़कियों की ऊँचाई (cm) के बारे में सूचना है।
(ii) 140-145 वर्ग में लड़कियाँ अधिकतम हैं।
(iii) 145 cm या उससे अधिक लम्बाई सात लड़कियों की है।
(iv) 2 + 1 = 3 लड़कियाँ समूह A के हैं।
7+ 4 = 11 लड़कियों समूह B के हैं।
1 + 2 + 3 = 6 लड़कियाँ समूह C के हैं।

पृष्ठ 83

प्रश्न 1.
निम्नलिखित पाई चार्टी में से प्रत्येक (आकृति) आपकी कक्षा के बारे में एक भिन्न प्रकार की सूचना देता है। इनमें से प्रत्येक सूचना को निरूपित करने वाले वृत्त का भाग ज्ञात कीजिए।

हल :
(i) पाई-चार्ट से स्पष्ट है,
लडकियों की संख्या = \(\frac{50%}{100%}\) = \(\frac{\frac{50}{100}}{\frac{100}{100}}\)
= \(\frac{50}{100}\) = वृत्त का \(\frac{1}{2}\) भाग

लड़कों की संख्या = \(\frac{50%}{100%}\) = \(\frac{\frac{50}{100}}{\frac{100}{100}}\)
= \(\frac{50}{100}\) = वृत्त का \(\frac{1}{2}\) भाग

(ii) पाई-चार्ट से स्पष्ट है,
पैदल आनेवालों की संख्या = \(\frac{40%}{100%}\) = \(\frac{\frac{40}{100}}{\frac{100}{100}}\)
= \(\frac{40}{100}\) = वृत्त का \(\frac{2}{5}\) भाग

बस अथवा कार से आनेवालों की संख्या = \(\frac{40%}{100%}\) = \(\frac{\frac{40}{100}}{\frac{100}{100}}\)
= \(\frac{40}{100}\) = वृत्त का \(\frac{2}{5}\) भाग

साइकिल से आने वालों की संख्या = \(\frac{20%}{100%}\) = \(\frac{\frac{20}{100}}{\frac{100}{100}}\)
= \(\frac{20}{100}\) = वृत्त का \(\frac{1}{5}\) भाग

(iii) पाई-चार्ट से स्पष्ट है,
गणित पसन्द करने वाले विद्यार्थी = \(\frac{(100-15)%}{100%}\) = \(\frac{\frac{85}{100}}{\frac{100}{100}}\)
= \(\frac{85}{100}\) = वृत्त का \(\frac{17}{20}\) भाग

गणित नापसन्द करने वाले विद्यार्थी = \(\frac{15%}{100%}\) = \(\frac{\frac{15}{100}}{\frac{100}{100}}\)
= \(\frac{15}{100}\) = वृत्त का \(\frac{3}{20}\) भाग

प्रश्न 2.
दिए हुए पाई चार्ट के आधार पर निम्नलिखित प्रश्नों के उत्तर दीजिए:

(i)किस प्रकार के कार्यक्रम सबसे अधिक देखे जाते हैं?
(ii) किन दो प्रकार के कार्यक्रमों को देखनेवालों की कुल संख्या खेलों के कार्यक्रमों को देखनेवालों की संख्या के बराबर है?
टी.वी. पर विभिन्न प्रकार के चैनलों को देखनेवालों की संख्या
हल :
उपर्युक्त पाई चार्ट से स्पष्ट है-
(i) मनोरंजन के कार्यक्रम सबसे अधिक देखे जाते हैं।
(ii)समाचार और ज्ञानप्रद कार्यक्रमों को देखनेवालों की कुल संख्या खेलों के कार्यक्रमों को देखनेवालों की संख्या के बराबर है।

पृष्ठ 85

प्रश्न 1.
नीचे दिए गए आंकड़ों के लिए एक पाई चार्ट खींचिए :
एक बच्चे द्वारा एक दिन में व्यतीत किया गया समय निम्नांकित प्रकार है:
सोना – 8 घण्टे
स्कूल – 6 घण्टे
गृहकार्य – 4 घण्टे
खेल – 4 घण्टे
अन्य – 2 घण्टे
हल :
इन आँकड़ों को पाई चार्ट में दर्शाते हैं। केन्द्र पर कुल कोण 360° के तथा त्रिज्यखण्ड कोण 360° के भाग होंगे।

हम नीचे दर्शाए अनुसार पाई चार्ट बनाएँगे :

सोचिए, चर्चा कीजिए और लिखिए (पृष्ठ 86)

निम्नलिखित आँकड़ों को दर्शाने के लिए किस प्रकार का आलेख उपयुक्त रहेगा ?

प्रश्न 1.
किसी राज्य के खाद्यान्न का ज्पादन :

हल :
दण्ड आलेख।

प्रश्न 2.
व्यक्तियों के एक समूह के भोजन की पसन्द :

हल :
वृत्त आलेख या पाई चार्ट।

प्रश्न 3.
किसी फैक्ट्री के श्रमिकों के एक समूह की दैनिक आय:

हल :
आयत चित्र।

प्रयास कीजिए (पृष्ठ 88-89)
प्रश्न 1.
यदि आप एक स्कूटर चलाना प्रारम्भ करें, तो सम्भव परिणाम क्या हैं?
हल :
स्कूटर चलाने के सम्भावित परिणाम होंगे
(i) स्कूटर चलेगा
(ii) स्कूटर नहीं चलेगा।

प्रश्न 2.
जब एक पासे (dice) को फेंका जाता है, तो सम्भव छः परिणाम क्या है?
हल :
एक पासे को फेंकने पर सम्भावित परिणाम पासे पर अंकित 1,2,3,4,5,6 में से कोई एक होगा।

प्रश्न 3.
जब आप पहिए को घुमाएंगे,तो सम्भावित परिणाम क्या होंगे (आकृति) ? इनकी सूची बनाइए।
[यहाँ परिणाम का अर्थ है कि वह त्रिज्यखण्ड, जहाँ पर सूचक (Pointer) घुमाने पर रुकेगा।]

हल :
पहिए को घुमाने के सम्भावित परिणाम होंगे-
(i) पहिया Aत्रिज्यखण्ड पर रुक सकता है।
(ii) पहिया B त्रिज्यखण्ड पर रुक सकता है।
(iii) पहिया C त्रिज्यखण्ड पर रुक सकता है।

प्रश्न 4.
आपके पास एक थैला है और उसमें भिन्न-भिन्न रंगों की पांच एक जैसी गेंदें हैं (आकृति) आप बिना देखे इसमें से एक गेंद निकालते हैं। प्राप्त होने वाले परिणामों को लिखिए।

हल :
एक थैला, जिसमें W, R, B,Gऔर Y गेंदें हैं। उनमें से निकलने वाली गेंद W, R, B,G और Y में से कोई एक होगी।

सोचिए, चर्चा कीजिए और लिखिए (पृष्ठ 89)

प्रश्न 1.
एक पासे को फेंकने पर :

• क्या पहले खिलाड़ी के 6 प्राप्त करने का संयोग अधिक है?
• क्या उसके बाद खेलने वाले खिलाड़ी के 6 प्राप्त करने का संयोग कम है?
• मान लीजिए कि दूसरा खिलाड़ी 6 प्राप्त कर लेता है। क्या इसका अर्थ यह है कि तीसरे खिलाड़ी द्वारा 6 प्राप्त करने का कोई संयोग नहीं है?

हल :
जब हम पासे को अनेकों बार फेंकते हैं, तो प्रत्येक बार 1 अथवा 2 अथवा 3 अथवा 4 अथवा 5 अथवा 6 में से 6 प्राप्त करने की सम्भावना समान अर्थात् 1/6 रहती है। इसलिए प्रत्येक खिलाड़ियों की दशा में 6 प्राप्त करने का संयोग समान है।

प्रयास कीजिए (पृष्ठ 91)

प्रश्न 1.
मान लीजिए कि आप पहिए को घुमाते हैं-

(i) इस पहिए पर एक हरा त्रिज्यखण्ड प्राप्त करने के परिणामों की संख्या और हरा त्रिज्यखण्ड प्राप्त न होने के परिणामों की संख्या लिखिए।
(ii) एक हरा त्रिज्यखण्ड प्राप्त करने की प्रायिकता ज्ञात कीजिए।
(iii) एक हरा त्रिज्यखण्ड प्राप्त नहीं होने की प्रायिकता ज्ञात कीजिए।
हल :
(i) दिए गए पहिए में एक हरा त्रिज्यखण्ड प्राप्त करने के परिणामों की संख्या = 5
और एक हरा त्रिज्यखण्ड प्राप्त नहीं करने के परिणामों की संख्या = 3
(ii) एक हरा त्रिज्यखण्ड प्राप्त करने की प्रायिकता = = \(\frac{5}{8}\)
(iii) एक हरा त्रिज्यखण्ड प्राप्त नहीं होने की प्रायिकता = 1 – \(\frac{5}{8}\) = \(\frac{3}{8}\)

Haryana State Board HBSE 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.4 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.4

प्रश्न 1.
बताइए, कश्चन सत्य हैं या असत्य
(a) सभी आयत वर्ग होते हैं ।
(b) सभी सम चतुर्भुज समान्तर चतुर्भुज होते हैं ।
(c) सभी वर्ग सम चतुर्भुज और आयत भी होते हैं ।
(d) सभी वर्ग समान्तर चतुर्भुज नहीं होते हैं ।
(e) सभी पतंगें सम चतुर्भुज होती हैं ।
(f) सभी सम चतुर्भुज पतंग होते हैं ।
(g) सभी समान्तर चतुर्भुज समलम्ब होते हैं ।
(h) सभी वर्ग समलम्ब होते हैं ।
हल :
(a) असत्य
(b) सत्य
(c) सत्य
(d) असत्य
(e) असत्य
(f) सत्य
(g) सत्य
(h) सत्य

प्रश्न 2.
उन सभी चतुर्भुजों की पहचान कीजिए, जिनमें-
(a) चारों भुजाएँ समान लम्बाई की हो ।
(b) चार समकोण हो ।
हल : (a) समचतुर्भुज और वर्ग →
(b) वर्ग और आयत →

प्रश्न 3.
बताइए कैसे एक वर्ग –
(i) एक चतुर्भुज
(ii) एक समान्तर चतुर्भुज
(iii) एक सम चतुर्भुज
(iv) एक आयत है।
हल :
(i) एक वर्ग में चार भुजाएँ होती हैं।
(ii) एक वर्ग की सम्मुख भुजाएँ समान्तर होती हैं ।
(iii) एक वर्ग की सभी भुजाएँ बराबर होती हैं तथा विकर्ण एक दूसरे को समकोण पर समद्विभाजित करते हैं ।
(iv) एक वर्ग के सभी कोण समकोण होते हैं ।

प्रश्न 4.
एक चतुर्भुज का नाम बताइए जिसके विकर्ण :
(i) एक-दूसरे को समद्विभाजित करते हों,
(ii) एक दूसरे पर लम्ब-समद्विभाजक हों,
(iii) बराबर हो ।
हल :
(i) समान्तर चतुर्भुज, सम चतुर्भुज, वर्ग, आयत के विकर्ण एक-दूसरे को समद्विभाजित करते हैं ।
(ii) समचतुर्भुज और वर्ग के विकर्ण एक-दूसरे को लम्ब-समद्विभाजित करते हैं ।
(iii) वर्ग और आयत के विकर्ण बराबर होते हैं।

प्रश्न 5.
बताइए एक आयत उत्तल चतुर्भुज है।
हल :
किसी आयत में जब हम इसके बिन्दुओं को मिलाते हैं, तो इसके दोनों विकर्ण अभ्यतंर में स्थित होते हैं तथा इसके प्रत्येक कोण 180° से कम होते है।

प्रश्न 6.
ABC एक समकोण त्रिभुज है। ‘0’ समकोण की सम्मुख भुजा का मध्यबिन्दु है । बताइए कैसे ‘0’ बिन्दु A, B तथा C से समान दूरी पर स्थित है ? (बिन्दुओं में चिह्नित अतिरिक्त भुजाएं आपकी सहायता के लिए खींची गई हैं।)
हल :

AD || BC तथा AB || CD की रचना की ।
ABCD एक समान्तर चतुर्भुज है और समान्तर चतुर्भुज के विकर्ण एक-दूसरे को समद्विभाजित करते हैं ।
∴ OA = OB = OC.
अत: O, बिन्दु A, B तथा C से समान दूरी पर है।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.3 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.3

प्रश्न 1.
ABCD एक समान्तर चतुर्भुज है। प्रत्येक कथन को परिभाषा या प्रयोग किये गये गुण द्वारा पूरा कीजिए।

(i) AD = ……………….
(ii) ∠DCB = ………..
(iii) OC = ………….
(iv) m ∠DAB + m ∠CDA = …………
हल :
(i) AD = BC (∵ समान्तर चतुर्भुज की सम्मुख भुजाएँ समान होती हैं ।)
(ii) ∠DCB = ∠DAB (∵ समान्तर चतुर्भुज के सम्मुख कोण समान होते हैं ।)
(iii) OC = OA (∵ समान्तर चतुर्भुज के विकर्ण । एक-दूसरे को समद्विभाजित करते हैं ।)
(iv) m∠DAB + m∠CDA = 180°. (∵ समान्तर चतुर्भुज में दो आसन्न अन्तःकोणों का योग 180° होता है।)

प्रश्न 2.
निम्नांकित समान्तर चतुर्भुजों में अज्ञात के मानों को ज्ञात कीजिए:

हल :
(i) समान्तर चतुर्भुज के सम्मुख कोण समान होते हैं।
अत: ∠D = ∠B तथा ∠A = ∠C
∴ y = 100°

समान्तर चतुर्भुज के दो आसन्न कोणों का योग = 180° होता है ।
∴ ∠A + ∠B = 180°
z + 100° = 180°
z = 180° – 100° = 80°
∴ z = 80°

परन्तु. ∠C = ∠A
∴ x = 80°
अतः x = 80°, y = 100° तथा z = 80°

(ii) समान्तर चतुर्भुज के दो आसन्न कोणों का योग 180° होता है।
∴ 50° + x = 180°
∴ x = 180°- 50° = 130°

अतः ∠x = 130°
परन्तु ∠x = ∠y
∠y = 130° (संगत कोण हैं)

तथा ∠x = ∠z
∠z = 130°
अतः x = 130°, y = 130° तथा z = 130°

(iii) ∠AOB = ∠COD शीर्षाभिमुख कोण है

90° = x
∴ x = 90°
∵ x + y + 30° = 180° (∵ ∆ COD के अन्त:कोणों का योग = 180° है)
⇒ 90° + y + 30° = 180°
⇒ y + 120° = 180°
⇒ y = 180° – 120° = 60°
∴ y = 60°
∵ एकान्तर कोण, y = z
∴ z = 60°
अतः x = 90°, y = 60° तथा z = 60°

(iv) समान्तर चतुर्भुज के सम्मुख कोण समान होते हैं ।

∴ ∠D = ∠B
∠D = 80°
अत: आसन्न अन्त:कोण हैं।
परन्तु, ∠A + ∠B = 180°
x + 80° = 180°
∴ x = 180°- 80° = 100°
अत: x = 100°

∵ AB || CD
z = ∠B (संगत कोण).
∴ z = 80°
अतः x = 100°, y = 80° तथा z = 80°

(v)
∵ ∠D = ∠B
∴ y = 112°
परन्तु, ∆ ACD में,
⇒ x + y + 40° = 180°
⇒ x + 112° + 40° = 180°
⇒ x + 152° – 180°
∴ x = 180° – 152° = 28°
अत: x = 28°

∵ CD || AB तथा AC तिर्यक् रेखा है
∴ x = z (एकान्तर कोण)
28° = z
∴ z = 28°
अतः x = 28°, y = 112° तथा z = 28°

प्रश्न 3.
क्या एक चतुर्भुज ABCD समान्तर चतुर्भुज हो सकता है, यदि:
(i) ∠D + ∠B = 180° ?
(ii) AB = DC = 8 सेमी, AD = 4 सेमी और BC = 4.4 सेमी ?
(iii) ∠A = 70° और ∠C = 65° ?
हल :
(i) ∠D+ ∠B = 180° वर्ग में यह कथन सत्य है, क्योंकि वर्ग के प्रत्येक अन्त:कोण का मान 90° होता है, परन्तु अन्य समान्तर चतुर्भुज में सम्भव नहीं है।

(ii) यह समान्तर चतुर्भुज नहीं हो सकता है: क्योंकि समान्तर चतुर्भुज की सम्मुख भुजाएँ समान होती है।
लेकिन यहाँ, AD ≠ BC

(iii) नहीं, क्योंकि समान्तर चतुर्भुज के सम्मुख कोण समान होते हैं।
अत: यहाँ ∠A ≠ ∠C.

प्रश्न 4.
एक चतुर्भुज की कच्ची आकृति खींचिए, जो समान्तर चतुर्भुज न झे, परन्तु जिसके दो सम्मुख कोणों की माप बराबर हो ।
हल :

पतंग ABCD में,
AB = AD तथा CB = CD है|
यह पतंग ABCD समान्तर चतुभुज नहीं है।
लेकिन, ∠ABC = ∠ADC
अतः इसके सम्मुख कोण बराबर होते हैं।

प्रश्न 5.
किसी समान्तर चतुर्भुज के दो आसन्न कोणों का अनुपात 3:2 है । समान्तर चतुर्भुज के सभी कोणों का मान ज्ञात कीजिए।
हल :

दिया है-दो आसन्न कोणों का अनुपात 3 : 2 है।
अत: दो आसन्न कोण 3x तथा 2x हैं।
∵ समान्तर चतुर्भुज के दो आसन्न कोणों का योग 180° होता है।
∵ ∠A + ∠B = 180°
⇒ 3x + 2x = 180°
⇒ 5x = 180°
x = \(\frac { 180° }{ 5 }\)
अतः ∠A = 3x = 3 × 36° = 108°
तथा ∠B = 2x = 2 × 36° = 72°

∵ समान्तर चतुर्भुज के सम्मुख कोण समान होते है।
अत: ∠C = ∠A = 108° तथा ∠D = ∠B = 72°
अत: ∠A= 108°, ∠B = 72°, ∠C= 108° तथा ∠D = 72°

प्रश्न 6.
किसी समान्तर चतुर्भुज के दो आसन्न कोणों की माप बराबर है। इस चतुर्भुज के सभी कोणों की माप ज्ञात कीजिए।
हल :
माना कि ABCD एक समान्तर चतुर्भुज है।
समान्तर चतुर्भुज के सम्मुख कोण समान होते हैं ।
∠A = ∠C
और ∠B = ∠D

∵ समान्तर चतुर्भुज के आसन्न कोणों का योग 180° होता है ।
∵ ∠A + ∠B = 180°

परन्तु, ∠A = ∠B
∠A + ∠A = 180°
∠2A = 180°
∠A = \(\frac{180°}{2}\) = 90°
अत: ∠A = ∠B = ∠C = ∠D = 90°
अतः प्रत्येक कोण 90° का होगा ।
अत: हम कह सकते हैं कि यह समान्तर चतुर्भुज, एक आयत या वर्ग होगा ।

प्रश्न 7.
संलग्न आकृति HOPE एकसमान्तर चतुर्भुज है। और कोणों की माप ज्ञात कीजिए । ज्ञात करने में प्रयोग किये गये गुणों को बताइए।
हल :
HOPE एक समान्तर चतुर्भुज है।
∆ HOP में,
∠HOP = 180° – 70° = 110°
अत: ∠HOP = 110°
समान्तर चतुर्भुज के आसन्न कोणों का योग 180° होता है।

अत: ∠EHO + ∠HOP = 180°
40° + z + 110° = 180°
150° + z = 180°
∠z = 180°- 150° = 30°
∠z = 30°

अब, AHOP में,
∠z + ∠y + ∠HOP = 180°
30° + ∠y + 110° = 180°
140° + ∠y = 180°
∠y = 180°- 140°- 40°
∠y = 40°

अब, समान्तर चतुर्भुज के सम्मुख कोण बराबर होते हैं।
∠HEP = ∠HOP
∠x = 110°
अतः ∠x = 110°
∠y = 40°, ∠z = 30°

प्रश्न 8.
निम्नांकित आकृतियों GUNS और RUNS समान्तर चतुर्भुज हैं । तथा । ज्ञात कीजिए । (लम्बाई cm में )-

हल :
(i)GUNS एक समान्तर चतुर्भुज है । समान्तर चतुर्भुज के आमने-सामने की भुजाएँ समान होती है। अत: GU = SN अत: 3y-1326
अतः ∴ GU = SN
अतः 3y – 1 = 26
⇒ 3y = 26 + 1
⇒ 3y = 27
⇒ y = \(\frac{27}{3}\) = 9
∴ y = 9

तथा 3x = 18
⇒ x = \(\frac{18}{3}\)
∴ x = 6
अत: x = 6 तथा y = 9

(ii) RUNS एक समान्तर चतुर्भुज हैं । समान्तर चतुर्भुज के विकर्ण एक-दूसरे को समद्विभाजित करते हैं ।
अतः OS = OU
तथा OR = ON
OS = OU
⇒ y + 7 = 20
⇒ y = 20 – 7
∴ y = 13

अब, ON = OR
⇒ x + y = 16
⇒ x + 13 = 16
⇒ x = 16 – 13
∴ x = 3
अत: x = 3 तथा y = 13

प्रश्न 9.
दी गई आकृति में RISK तथा CLUE दोनों समान्तर चतुर्भुज है,* का मान ज्ञात कीजिए।

हल :
RISK तथा CLUE समान्तर चतुर्भुज हैं।

(i) समान्तर चतुर्भुज RISK में,
∠K + ∠S = 180°
⇒ 120° + ∠S = 180°
⇒ ∠S = 180°- 120° = 60°
अत: ∠S = 60°

अब, समान्तर चतुर्भुज CLUE में,
हम जानते हैं कि सम्मुख कोण समान होते हैं ।
∴ ∠L = ∠E
∴ ∠E = 70°

∆EOS में,
∆ के तीनों कोणों का योग 180° होता है।
∴ ∠E + ∠O + ∠S = 180°
⇒ 70° + x + 60° = 180°
⇒ 130° + x = 180°
⇒ ∠x = 180° – 130° = 50°
अतः x = 50°

प्रश्न 10.
बताइए कैसे यह आकृति एक समलम्ब है। इसकी कौन सी दो भुजाएँ समान्तर 80 हैं?

हल :
समलम्ब में, अन्तः आसन्न कोणों का योग 180° होता है।
अत: ∠M + ∠L = 180°
⇒ 100° + 80° = 180°
∴ 180° = 180°
इसलिए, KLMN एक समलम्ब है ।
⇒ \(\overline{\mathrm{NM}}\) || \(\overline{\mathrm{KL}}\).

प्रश्न 11.
निम्न आकृति में m∠C ज्ञात कीजिए, यदि \(\overline{\mathrm{AB}}\) || \(\overline{\mathrm{DC}}\).

हल :
दिया है, AB || DC
अतः, आसन्न अन्त:कोणों का योग = 180°
⇒ ∠B + ∠C = 180°
⇒ 120°+ ∠C = 180°
⇒ ∠C = 180° – 120° = 60°
अतः ∠C = 60°.

प्रश्न 12.
संलग्न आकृति में s ∠P तथा ∠S की माप ज्ञात | कीजिए । यदि \(\overline{\mathrm{SP}}\).\(\overline{\mathrm{RQ}}\) है । (यदि आप m∠R ज्ञात करते है, तो क्या m∠P को ज्ञात करने की एक से अधिक विधि है।)

हल :
दिया है, SP || RQ. अत: अन्तः आसन्न कोणों का योग = 180°
∴ ∠P + ∠Q = 180°
⇒ ∠P + 130° = 180°
⇒ ∠P = 180° – 130° = 50°
∴ ∠P = 50°

अब, ∠R + ∠S = 180°
∠S + 90° = 180°
∠S = 180° – 90° = 90°
∠S = 90°
अत:, ∠P = 50° तथा ∠S = 90°

हाँ, m∠P ज्ञात करने की अन्य विधि भी है।
∴ चतुर्भुज में चारों कोणों का योगफल 360° होता है।
m∠P + m∠Q + m∠R + m∠S = 360°
⇒ m∠P + 130° + 90° + 90° = 360°
⇒ m∠P = 360° – 310°
∴ m∠P= 50°

Haryana State Board HBSE 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.2 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.2

प्रश्न 1.
निम्नलिखित आकृतियों में x का मान ज्ञात कीजिए-

हल :
(a) बहुभुज के बाह्य कोणों का योग = 360°
∴ ∆ABC में,

125° + 125° + x = 360°
250° + x = 360°
∴ x = 360° – 250° = 110°
अतः x = 110°

(b) ABCDE एक पंचभुज है।

दिया है, अन्त:कोण, ∠B = 90°
बाह्य कोण, ∠B = 90°
बाघ कोण, ∠D = 90°
बहुभुज के बाझ कोणों का योग = 360°
अत: x + 90° + 60° + 90° + 70° = 360°
⇒ x +310° = 360°
⇒ x = 360°- 310° = 50°
∴ x = 50°

प्रश्न 2.
एक समबहुभुज के प्रत्येक बाह्य कोण की माप ज्ञात कीजिए, जिसकी-
(i) भुजाएँ
(ii) 15 भुजाएँ हों।
हल :
भुजाओं वाले एक समबहुभुज के प्रत्येक कोण की माप = 360°
(i) n = 9, प्रत्येक बाह्य कोण की माप = \(\frac{360°}{9}\) = 40°

(ii) n = 15, प्रत्येक बाह्य कोण की माप = \(\frac{360°}{15}\) = 24°

प्रश्न 3.
एक समबहुभुज की कितनी भुजाएं होंगी, यदि एक बाह्य कोण की माप 24° हो ?
हल :
भुजाओं वाले एक सम बहुभुज के प्रत्येक बाह्य कोण की माप = 360°
अतः
24° = \(\frac{360°}{n}\)

कैंची गुणा करने पर,
24°n = 360°
∴ n = \(\frac{360°}{24}\) = 15
अतः भुजाओं की संख्या, n = 15

प्रश्न 4.
एक समबहुभुज की भुजाओं की संख्या ज्ञात कीजिए, यदि इसका प्रत्येक अन्त:कोण 165 का हो।
हल :
हम जानते हैं कि n भुजाओं वाले समबहुभुज के प्रत्येक अन्त:कोण का मान =\(\frac{(n-2) \times 1800^{\circ}}{n}\)
अतः \(\frac{(n-2) \times 1800^{\circ}}{n}\) = \(\frac{165}{1}\)

कैंची गुणा करने पर, 180°n – 360° = 165°n
पक्षान्तरण करने पर, 180°n – 165°n = 360°
15°n = 360°
∴ n = 24°
अतः समबहुभुज की भुजाओं की संख्या, n = 24

प्रश्न 5.
(a) क्या ऐसा समबहुभुज सम्भव है, जिसके. प्रत्येक बाह्य कोण की माप 22 हो ?
(b) क्या यह किसी समबहुभुज का अन्तःकोण हो सकता है? क्यों ?
हल :
(a) n भुजाओं वाले समबहुभुज के प्रत्येक बाह्य कोण की माप \(\frac{360°}{n}\)
\(\frac{22°}{1}\) = \(\frac{360°}{n}\)

कैंची गुणा करने पर, 22°n = 360°
∴ n = \(\frac{360°}{22}\) = \(\frac{180°}{24}\)

लेकिन भुजाओं की संख्या कभी भिन्न में सम्भव नहीं है।
अतः ऐसा समबहुभुज सम्भव नहीं है, जिसका प्रत्येक बाह्य कोण 22° का हो ।

(b) n भुजाओं वाले समबहुभुज के प्रत्येक अन्त:कोण की माप = \(\frac{(n-2) \times 180^{\circ}}{n}\)
अत: \(22^{\circ}=\frac{(n-2) 180^{\circ}}{n}\)
⇒ \(\frac{22^{\circ}}{1}=\frac{180^{\circ} n-360^{\circ}}{n}\)
कैंची गुणा करने पर, 180°n – 360° = 22°n
पक्षान्तरण करने पर, 180°n – 22°n = 360°
⇒ 158°n = 360°
⇒ n = \(\frac{360°}{158°}\) = \(\frac{180°}{79°}\)

अतः n = \(\frac{180°}{79°}\)
अत: यह भी सम्भव नहीं है, क्योंकि भुजाओं की संख्या भिन्न में नहीं हो सकती है।

प्रश्न 6.
(a) किसी समबहुभुज में कम-से-कम कितने अंश का अन्तःकोण सम्भव है ? क्यों ?
हल :
समबहुभुज में कम-से-कम 3 भुजाएँ होनी चाहिए। अत: कम-से-कम अंश का अन्त:कोण
\(\frac{(3-2) \times 180^{\circ}}{3}\) = \(\frac{1 × 180°}{3}\) = 60°
अतः सम्भव अन्त:कोण = 60°

(b) किसी समबहुभुज में अधिक-से-अधिक कितने अंश का बाह्य कोण सम्भव है?
हल :
कम-से-कम अंश का अन्त:कोण = 60°
इसलिए, ज्यादा-से-ज्यादा अंश का बाह्य कोण = 180° – 60° = 120°

Haryana State Board HBSE 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.1 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 3 चतुर्भुजों को समझना Ex 3.1

प्रश्न 1.
यहाँ पर कुछ आकृतियाँ दी गई हैं-

प्रत्येक का वर्गीकरणं निम्नलिखित आधार पर कीजिए
(a) साधारण वक्र
(b) साधारण बंद वक्र
(c) बहुभुज
(d) उत्तल बहुभुज
(e) अवतल बहुभुज
हल :
(a) साधारण वक्र – 1, 2, 5, 6, 7
(b) साधारण बन्द वक्र – 1, 2, 5, 6, 7
(c) बहुभुज – 1, 2, 4
(d) उत्तल बहुभुज – 2
(e) अवतल बहुभुज – 1, 4.

प्रश्न 2.
निम्नलिखित प्रत्येक में कितने विकर्ण हैं
(a) एक उत्तल चतुर्भुज
(b) एक समषड्भुज
(c) एक त्रिभुज
हल :
(a) एक उत्तल चतुर्भुज में दो विकर्ण होते हैं।

(b) एक समषड्भुज में 9 विकर्ण होते हैं।

(c) त्रिभुज में कोई विकर्ण नहीं होता है ।

प्रश्न 3.
उत्तल चतुर्भुज के कोणों की मापों का योगफल क्या है ? यदि चतुर्भुज उत्तल न हो, तो क्या यह गुण लागू होगा?
हल :

ABCD एक उत्तल चतुर्भुज है और B तथा D को मिलाते हैं। हमें दो त्रिभुज, ∆ABD, तथा ∆BCD प्राप्त होते हैं।
एक त्रिभुज के अन्तःकोषों का योग = 180°
इसी प्रकार दूसरे त्रिभुज के अन्त:कोणों का योग = 180°
अत: दोनों त्रिभुजों के अन्त:कोणों का योग = 180° + 180° = 360°
अत: उत्तल चतुर्भुज ABCD के कोणों का योग = 360°

अब माना, PQRS एक अवतल चतुर्भुज है । P और R को मिलाते हैं।
हमें दो त्रिभुज, ∆PQR तथा ∆PRS प्राप्त होते हैं ।
अब ∆PQR के कोणों का योग = 180°
तथा ∆PRS के कोणों का योग = 180°
अतः अवतल चतुर्भुज के कोणों का योग, = 180° + 180° = 360°
अत:, यदि चतुर्भुज उत्तल न हो, तो भी यह गुण लागू होता है ।

प्रश्न 4.
तालिका की जाँच कीजिए : (प्रत्येक आकृति को त्रिभुजों में बाँटिए और कोणों का योगफल ज्ञात कीजिए ।)

एक बहुभुज के कोणों के योग के बारे में आप क्या कह सकते हैं, जिसकी भुजाओं की संख्या निम्नलिखित हो?
(a) 7
(b) 8
(c) 10
(d) n
हल :
(a) बहुभुज के कोणों का योग = (n – 2) × 180°
n = 7, कोणों का योग = (7 – 2) × 180° = 5 × 180°
अतः योग = 900°

(b) n = 8, कोणों का योग = (8 – 2) × 180°
= 6 × 180° = 1080°
अतः योग = 1080°

(c) n = 10, कोणों का योग = (10 – 2) × 180°
= 8 × 180° = 1440°
अत: योग = 1440°

(d) n = n, कोणों का योग = (n – 2) × 180°

प्रश्न 5.
सम बहुभुज क्या है? एक सम बहुभुज का नाम बताइये, जिसमें-
(i) 3 भुजाएँ
(ii) 4 भुजाएँ
(iii) 6 भुजाएं हों।
हल :
सम बहुभुज-वह बहुभुज, जिसकी सभी भुजाएँ. एवं सभी कोण समान होते हैं, उसे सम बहुभुज कहते हैं ।
(a) 3 भुजाएँ वाले सम बहुभुज का नाम-समबाहु त्रिभुज
(b) 4 भुजाएँ वाले सम बहुभुज का नाम-वर्ग
(c) 6 भुजाएँ वाले सम बहुभुज का नाम-समषट्भुज

प्रश्न 6.
निम्नलिखित आकृतियों में (कोणों की माप) ज्ञात कीजिए

हल :
(a) ABCD एक चतुर्भुज है, जिसके चारों कोणों का योग = 360°

अतः ∠A+ ∠B+ ∠C+ ∠D = 360°
⇒ 50° + 130° + 120° + x = 360°
⇒ 300° + x = 360°
⇒ x = 360° – 300 = 60°
अत: , x = 60°

(b) चतुर्भुज ABCD के अन्त:कोण का मान अन्त:कोण ∠A = 180° – 90° = 90°
अत: ∠A = 90°

अब, ∠A + ∠B + ∠C + ∠D = 360°
90° + 60° + 70° + x = 360°
⇒ 220° + x = 360°
x = 360° – 220° = 140°
अतः x = 140°

(c) अन्त:कोण ∠A= 180° – 70°
∠A = 110°

अन्त:कोण ∠E = 180° – 60°
∠E = 120°
A अब, पंचभुज ABCDE के अन्त:कोणों का योग = (n – 2) × 180°
= (5 – 2) × 180° = 3 × 180° = 540°

अत: ∠A+ ∠B + ∠C+ ∠D + ∠E = 540°
⇒ 110° + x + 30 + x + 120° = 540°
⇒ 2x + 260° = 540°
⇒ 2x = 540° – 260°
⇒ 2x = 280°
∴ x = \(\frac{280}{2}\) = 140°
अत: x = 140°

(d) ABCDE एक समपंचभुज है।
∠A = ∠B = ∠C = ∠D = ∠E = x
समपंचभुज के कोणों का योग = (5 – 2) × 180°
= 3 × 180°
= 540°

∠A + ∠B + ∠C + ∠D + ∠E = 540
⇒ x + x + x + x = 540°
5x = 540°
∴ x = \(\frac{540°}{5}\) = 108°

अतः x = 108°

प्रश्न 7.
(a) x + y + z ज्ञात कीजिए।

(b) x + y + z + w ज्ञात कीजिए।

हल :
(a) बहुभुज के बा कोणों का योग = 360°
x, y, z, बहिष्कोण हैं ।
x + y + z = 360°

(b) बाह्य कोणों का योग = 360°
x, y, z, w बहिष्कोण हैं।
x + y + z + w = 360°

Haryana State Board HBSE 8th Class Science Solutions Chapter 13 Sound Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 13 Sound

HBSE 8th Class Science Sound Textbook Questions and Answers

Question 1.
Choose the correct answer: Sound can travel through:
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases.
Answer:
(d) solids, liquids and gases.

Question 2.
Voice of which of the following is likely to have minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Answer:
(a) Baby girl.

Question 3.
In the following statements, tick ‘T’ against those which are true and ‘F’ against those which are false :
(a) Sound cannot travel in vacuum. (T / F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T / F)
(c) If the amplitude of vibration is large, sound is feeble. (T / F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T / F)
(e) The lower the frequency of vibration, the higher is the pitch. (T / F)
(f) Unwanted or unpleasant sound is termed as music. (T / F)
(g) Noise pollution may cause partial hearing impairment. (T / F)
Answer:
(a) True
(b) False
(c) False
(d) True
(e) False
(f) True
(g) True.

Question 4.
Fill in the blanks with suitable words :
(a) Time taken by an object to complete one oscillation is called ________.
(b) Loudness is determined by the ________ of vibration.
(c) The unit of frequency is ________.
(d) Unwanted sound is called ________.
(e) Shrillness of a sound is determined by the ________ of vibration.
Answer:
(a) time period
(b) amplitude
(c) hertz
(d) noise
(e) frequency.

Question 5.
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
Time taken by pendulum to complete 40 oscillations = 4 seconds
Time taken by pendulum
to complete 1 oscillation = \(\frac { 4 }{ 40 }\)
= \(\frac { 1 }{ 10 }\)
= 0.1 sec.
Time period of pendulum = 0.1 sec.
Frequency of pendulum
= \(\frac { 40 }{ 4 }\) \(\frac { oscillation }{ time }\)
= 10 Hz.

Question 6.
The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Answer:
Time taken to complete
500 vibrations = 1 second
Time taken to complete
1 vibration = \(\frac { 1 }{ 500 }\) = 0.002
Time period of vibration = 0.002 second.

Question 7.
Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak
(b) Sitar
(c) Flute.
Answer:
(a) Stretched membrane
(b) Strings
(c) air column.

Question 8.
What is the difference between noise and music? Can music become noise sometimes?
Answer:
Noise is the sound which is unpleasant for our ears. Excessive or unwanted sounds are called noise. Music is the sound which is pleasant for our ears and has soothing effect. Music sometimes can become noise when it crosses the bearable range of sound for our ears.

Question 9.
List sources of noise pollution in your surroundings.
Answer:
There are various sources which cause sound pollution in our surroundings like : Honking of horns, loud sounds of machines in factories, loud musics in parties and marriages, loud sound of T. V. or radio, loud sounds of domestic electronic appliances like mixer grinder etc. are some sources of noise in our environment.

Question 10.
Explain in what way noise pollution is harmful to humans?
Answer:

• Noise pollution can cause temporary or permanent deafening.
• It can cause many health related problems like high blood pressure
• It can cause mental illness due to lack of sleep.

Question 11.
Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer:
I would suggest my parents to buy house three lanes away from the roadside because area away from the roadside have less traffic and thus less noise pollution. This would safe guard our health and peace of mind.

Question 12.
Sketch larynx and explain its function in your own words.
Answer:
Larynx is also called the voice box. As the name suggests, it causes (sound) voice in humans. It has vocal cords, which have air column vibrating in them, which cause sound in humans.

Question 13.
Lightening and thunder take place in the sky at the same time and at the same distance from us. Lightening is seen earlier and thunder is heard later. Can you explain?
Answer:
Lightening and thundering take place simultaneously but we see light earlier than thunder because light travels faster than sound, so it reaches us before the sound does.

Extended Learning – Activities and Projects

Question 1.
Visit the music room of your school. You may also visit musicians in your locality. Make a list of musical instruments. Note down the parts of these instruments that vibrate to produce sound.
Answer:
For self attempt.

Question 2.
If you play a musical instrument, bring it to the class and demostrate how you play it.
Answer:
For self attempt.

Question 3.
Prepare a list of famous Indian musicians and the instruments they play.
Answer:
For self attempt.

Question 4.
Take a long thread. Place your hands over your ears and get some one to place this thread round your head and hands. Ask her to make the thread taut and hold its ends in the hand. Now ask her to draw her finger and thumb tightly along the thread (in figure). Can you hear a rolling sound like that of a thunder ? Now repeat the activity while another friend stands near both of you. Can he hear any sound.

Answer:
For self attempt.

Question 5.
Make two toy telephones. Use them as shown in Fig. Make sure that the two srtings are taut and touch each other. Let one of you speak. Can the remaining three persons hear? See how many more friends you can engage in this way. Explain your observations.

Answer:
For self attempt.

Question 6.
Identify the sources of noise pollution in your locality. Discuss with your parents, Mends wad neighbours. Suggest how to control noise pollution. Prepare a brief report and present it in the class.
You can read more on the related topics on the following websites:
→ www.physicsclassroom .com/Class/sound/soundtoc.html
→ health.howstuffworks.com/hearing.htm
→ www.jaltarang.com for jaltarang
→ www.tempro/com/articles/hearing.html
→ www.cartage.org.lb/en/themes/sciences/ physics/mainpage.htm
Answer:
For self attempt

HBSE 7th Class Science Sound Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What produces sound?
Answer:
Vibrations in body produce sound.

Question 2.
Can sound be produced from a body which does not vibrate?
Answer:
No.

Question 3.
Why can’t we see the vibrations in most of the cases when sound is produced?
Answer:
Their amplitude is very small.

Question 4.
Name any wind musical instrument.
Answer:
Flute.

Question 5.
What is the sound producing organ in humans called?
Answer:
Larynx.

Question 6.
What is another name for larynx?
Answer:
Voice box.

Question 7.
What are the two cords stretched across the voice box called?
Answer:
Vocal cords.

Question 8.
What vibrates in larynx to produce sound?
Answer:
Vocal cords.

Question 9.
What decides the type of voice in human?
Answer:
Tightness of vocal cords.

Question 10.
How much long the vocal cords are in men?
Answer:
20 mm.

Question 11.
What is the length of vocal cords in women?
Answer:
15 mm.

Question 12.
Through which medium can sound travel?
Answer:
Solids, liquid and gaseous medium.

Question 13.
Can sound travel through vacuum?
Answer:
No.

Question 14.
Which organs in human receive sound waves? .
Answer:
Ears.

Question 15.
What is the outer stretched part of the ear called?
Answer:
Ear drum.

Question 16.
What vibrates the ear drum?
Answer:
Sound vibrations.

Question 17.
What is the to and fro motion of objects called?
Answer:
Oscillatory motion.

Question 18.
What is the frequency of oscillation?
Answer:
Number of oscillations per second is called frequency of oscillation.

Question 19.
What is the unit of frequency?
Answer:
Hertz (Hz).

Question 20.
What does a frequency of 1 Hz means?
Answer:
One oscillation in one second.

Question 21.
What are the two important properties of a sound?
Answer:
Amplitude and frequency.

Question 22.
What is the maximum distance travelled by a vibrating body on either side of its mean position called?
Answer:
Amplitude.

Question 23.
What is the time taken to complete one oscillation called?
Answer:
Time period.

Question 24.
How does amplitude effect the loudness of vibration?
Answer:
Higher the amplitude, louder is the voice.

Question 25.
Why the sound of a baby is feeble?
Answer:
Because its amplitude is small

Question 26.
What controls the shrillness of a sound?
Answer:
Frequency.

Question 27.
What is the range of audible sound for human ear?
Answer:
From 20 to 20,000 Hz.

Question 28.
What are the sounds above 20,000 ‘ Hz called?
Answer:
Ultrasound.

Question 29.
Name any use of ultrasound?
Answer:
Ultrasound is used to detect many medical problems in human.

Question 30.
What is the unpleasant and unwanted sound called?
Answer:
Noise.

Question 31.
What are the pleasant and soothing sounds called?
Answer:
Music.

Question 32.
What is the unit of loudness?
Answer:
Decibel (dB).

Question 33.
What is the loudness of a normal conversation?
Answer:
60 dB.

Question 34.
Name any ill effect of noise pollution.
Answer:
It can cause temporary deafness.

Question 35.
Write any one measure to control noise pollution.
Answer:
Planting trees along roadsides.

Short Answer Type Questions

Question 1.
How is sound produced?
Answer:
Sound is produced by the vibrating bodies. When a body vibrates it produces sound.

Question 2.
What is the importance of sound in our life?
Answer:
Our life depends on sound for every action. Sound enables us to communicate with each other. Without sound nobody would know what other communicate or wants to express.

Question 3.
What are the musical instruments?
Answer:
Musical instruments are the devices which produce various sounds which are pleasant for our ears and produce soothing effects. The sound produced by these instruments is called music.

Question 4.
How do the musical instruments produce sound?
Answer:
Musical instruments have strings the stretched membranes attached or fixed on them . Some instruments have slits to let air pass through them, the strings are plucked and membranes are struck to produce sound. On plucking or striking they start vibrating, and the whole instrument starts vibrating with them, which produces the music.

Question 5.
Describe the organ in human that produces sound.
Answer:
In humans the sound producing organ is the voice box. It is also called the larynx. In larynx there are two vocal cords stretched across, leaving a slit for the air to pass through them.

Question 6.
How does the larynx produce sound?
Answer:
Larynx has two vocal cords stretched across it. They are stretched in a way that they leave a slit for passage of air. When air is pumped in slit by the lungs, the vocal cords start vibrating, thus producing the sound.

Question 7.
What distinguishes the sounds produced by different human beings from each other?
Answer:
Vocal cords in humans are the sound producing parts. When they are vibrated they produce sound. They are held by the muscles and the tightness with which they are held determines the quality of sound. The length of the vocal cords also determines the quality of voice.

Question 8.
How is the sound propagated?
Answer:
The sound reaches from one source to another through various mediums. It always needs a medium to travel, it cannot propagate through vacuum. Sound travels through air, solid and liquid.

Question 9.
How is it possible for whales and dolphins to communicate in water?
Answer:
Whales and dolphins live under water. They produce sound to communicate with each other. As sound can travels through air, solid and liquid-all the mediums, it is travelled from one source to another in water too, so dolphins and whales can communicate.

Question 10.
How do human hear the sounds?
Answer:
Humans hear various sounds through ears. Ears have a stretched structure called eardrum. When ears receive sound, it enters down the earcanal and reach eardrum. Vibrations of sound vibrates the eardrum and it sends vibrations to inner ear from which vibrations are sent to brain for interpretation of sound.

Question 11.
Why is it advised, not to put a sharp or pointed thing in our ear?
Answer:
It is advised not to put sharp or pointed things in the ear because it can damage the eardrum. Eardrum is a stretched membrane which is delicate. If the sharp or pointed thing would touch the eardrum, it would damage the eardrum and cause deafness.

Question 12.
What is oscillatory motion?
Answer:
The to and fro motion of the object is called vibration. This motion is the movement in both direction from its mean position- This motion in either side of the object from its mean position is called the oscillatory motion.

Question 13.
What is frequency of a motion?
Answer:
The number of to and for movement or number of oscillations per second is called the frequency of a motion. Frequency is expressed in Hertz. It is symbolized as Hz.

Question 14.
How does frequency effect the quality of sound?
Answer:
The frequency determines the shrillness of the sound. Shrillness is also called the pitch of sound. The pitch of the sound is higher if it has high frequency and the pitch is low if the frequency is less.

Question 15.
What controls the quality of voice in humans?
Answer:
Amplitude and frequency of vibrations control voice in human beings. If amplitude is high the loudness of sound will also be high, if frequency is high the shrillness or pitch will be high in voice.

Question 16.
Describe the properties of voice in men.
Answer:
Men have high amplitude of vibrations so their voice is loud and they have low frequency so-they have less shrillness in their voice.

Question 17.
Describe the properties of voice in women.
Answer:
Women have high frequency of sound waves, so they have high pitched voice it means they have high shrillness in their voice. On the other hand they have low amplitude so they have less loudness in their voice.

Question 18.
Describe the audible range of fequencies for human beings.
Answer:
Human beings cannot hear sounds below 20 Hz that means sounds with less than 20 vibrations per second cannot be heard by human beings. On the other hand sounds with frequency more than 20 KHZ also cannot be heard by human beings. 20 KHz means 20,000 vibrations per second. Therefore, roughly the audible range of sounds for human beings vary between 20 Hz to 20 KHz.

Question 19.
What are ultrasounds? How are they useful to us?
Answer:
Sounds with frequency of above than 20 KHz are called ultrasound. Ultrasounds cannot be heard by human beings, but they are very useful for human beings. Ultrasounds are used in field of medicine to detect the disorders inside the body of human beings. They are also useful in industries. They are used to detect the flaws and cracks in metallic structures.

Question 20.
What is noise?
Answer:
Noise is the unwanted and unpleasant sounds reaching our ears. They cause disturbance and are harmful. Noise is the sound which crosses the limit of audible loudness for us. Normally sounds at 80 dB of loudness becomes painful to bear and is called noise.

Question 21.
Give any five sources of noise in your surroundings.
Answer:
Five sources of noise in our environment are :

• Noise made by traffic.
• Noise created by electrical appliances used at home like coolers, mixer grinder etc.
• Loud sounds of T.V., Radio etc.
• Noise created by loud music in marriages and religious functions.
• Noise created by construction works in neighbourhood.

Question 22.
What do you mean by hearing impairment? How is it caused?
Answer:
Hearing impairment means disability to hear. It is caused by diseases of ear, injury of ear or due to degeneration of hearing mechanism with growing age. Hearing impairment can be overcome by using hearing aids if impairment is not permanent.

Question 23.
How can hearing impairment be overcome or avoided?
Answer:
Hearing impairment can be avoided by avoiding noise or avoiding the usage of sharp of pointed objects inside ear, We should avoid any ear injury. In case of hearing impairment which is temporary hearing aids help in overcoming it or using other aids like sign language etc.

Question 24.
What is noise pollution?
Answer:
Presence of excessive or unwanted sounds in the environment, which cause discomfort for us is called noise pollution. Excessive sounds are produced by honking of horns, loud speakers, crackers, machines etc.

Question 25.
How can noise pollution be controlled?
Answer:
Noise pollution can be controlled by controlling their sources. Blowing of horns should be avoided in residential areas, near schools or hospitals. Using loudspeakers etc. should also be avoided in these areas. T.V., radio etc should be played at low volume. Trees should be planted along the roadside to create a buffer zone to absorb excessive sounds on roads.

Long Answer Type Questions

Question 1.
How is sound produced? How does it travel from one place to another?
Answer:
Sound is produced by the vibrations of the body. Only vibrating bodies produce sound. Those bodies which produce vibrations produce sound but when they stop vibrating they also stop producing sound.
Sound reaches from one source to another. It travels from one point to another through some medium. Sound waves can travel through air, liquid and even through solids. What we hear one another, that sound travels through air medium. But we can bear some body talking in next room too, that means sound waves have crossed wall to reach us. Dolphins and whales communicate in water.

Question 2.
Explain hew many types of musical instruments are there? Hew die they make sound?
Answer:
Musical instruments are differentiated on the basis of their vibrating parts, Some musical instruments have sretched membranes Which produce vibrations to make sound. Second type of musical instruments have stretched strings, which vibrate to produce sound. In third v type of instruments the wind column is used to ’ produce sound.

Instruments like hands, drums, mridangam etc, have stretched leather membrane which is struck with hands or stick to produce sounds. In instruments like guitar, sitar, veena, violin etc,, strings are struck with fingers or rubber with other instruments produce musical sounds. Instruments like mouth-organ, sehnai, flute etc, use air column to produce sounds.

Question 3.
What is nuisa? Haw is noise pollution created?
Answer:
Noise is the unwanted and unpleasant sounds around us in our environment. When these noises become huge, it creates noise pollution. Different, loud and shrill sounds discharged in environment cause noise pollution. Honking horns of vehicles on road, loud music of T-Vs and Radios, loud music in marriages and parties, noise of machines in factories, domestic electrical appliances like mixer grinder, construction work in neighbourhood, etc. are the ‘ various sources of noise polluiton in our environment.

Question 4.
What are the ill-effects of noise pollution? How can we control noise pollution?
Answer:
Noise pollution has many bad effects on our body and health. Our health and mental peace are adversely affected by noise pollution. Noise pollution becomes the root cause of many mental disorders like anxiety, depression etc. Besides mental disorders, physical disorders like hypertension, skin diseases, lack of sleep etc. are also caused by noise pollution. It is more harmfid for students and sick people.

For controlling noise pollution, honking of horns from vehicles should he banned near residential areas, schools and hospitals. T.Vs. and Radios should be played at low volume. Loudspeakers should not be allowed during sleeping hours. Trees and plants should be extensively planted along the road sides to create a buffer zone. Trees absorb noise and help in controlling noise pollution.

Sound Class 8 HBSE Notes

1. We hear different sounds in our daily life.

2. Sound is produced by the vibrating bodies. Only vibration can produce sound. Vibrations are to and fro movements of any object and this to and fro movements produce different sounds we have.

3. When the vibrations start, we hear sound, but when vibrations stop, the sound is not heard anymore.

4. Different musical instruments produce sound only due to the vibrations made by them, when they are beaten or plucked by us.

5. It is not only the vibrations of the strings or the stretched membranes of the musical instruments that produce sound, but it is the vibration of the whole instruments that produce sound.

6. In human beings it is the vibrations of the voice box or the larynx that causes the sound. Air passing through the vocal cords attached to larynx cause vibrations of the vocal cords, which enables us to produce sound.

7. It is the tightness of the vocal cords that make sounds different from each other in different human beings. The length of the vocal cords are different in men, women and children, so their voice is also different from each other.

8. Sound cannot pass from one source to another in vacuum. Sound needs medium to travel. Air, liquid, solid are the medium through which sound can travel from one source to another.

9. In human beings sound is produced by voice box, and received by hearing organs-ears. Receiving sound is called hearing. Our ear is so designed that it receives the vibrations and interpret it as sound.

10. The maximum distance a vibrating body travels from its means position is called amplitude of vibration.

11. The time taken to complete one oscillation (to and fro movement) is called the time period.

12. The number of oscillation per second is called the frequency of vibration. Frequency is expressed in Hertz (Hz).

13. Higher the frequency of vibration, higher is the pitch or shrilners of the sound.

14. High amplitude of vibration produces loud sound.

15. Unpleasant or unwanted sounds are called noises.

Haryana State Board HBSE 8th Class Science Solutions Chapter 6 Combustion and Flame Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 6 Combustion and Flame

HBSE 8th Class Science Combustion and Flame Textbook Questions and Answers

Question 1.
List conditions under which combustion can take place.
Answer:
Following conditions are necessary for combustion:
(i) The substance should be combustible.
(ii) It should have low ignition temperature.
(iii) There should be proper supply of air.

Question 2.
Fill in the blanks:
(a) Burning of wood and coal causes …………. of air.
(b) A liquid fuel, used in homes is …………. .
(c) Fuel must be heated to its before it …………. starts burning.
(d) Fire produced by oil cannot be controlled by …………. .
Answer:
(a) pollution
(b) Kerosene
(c) ignition temperature
(d) water.

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer:
CNG has replaced petrol and diesel as fuel in automobiles because petrol and diesel produced a lot of unbumt carbon particles and emitted carbondioxide and nitrogen oxides and sulphur dioxide. These all gases are poisonous gases and cause various environmental hazards. But CNG is safe because it produces these substances in very small amounts thus reducing pollution in cities.

Question 4.
Compare LPG and wood as fuels.
Answer:

Question 5.
Give reasons:
(a) Water is not used to control the fire involving electrical equipment.
(b) LPG is a better domestic fuel than wood.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not. .
Answer:
(a) Water is a conductor of electricity, so it can easily conduct electric current and causes danger of electric shocks.
(b) LPG is a better domestic fuel than wood because unlike wood it does not produce smoke and is comparatively easy to transport.
(c) Paper by itself catches fire easily because it has low ignition temperature but when wrapped around an aluminium pipe its

Question 6.
Make a labelled diagram of a candle flame.
Answer:

Different Zones of Candle flame

Observe the foaming reaction. What happens to the candles? Why? In what order?

Answer:
The candles get extinguished. The smaller candle with get extinguisher first because thfe supply of oxygen is cut of due to foam; The smaller candle will come in effect of foam earlier than the longer one and thus stop burning prior to the longer candle.

Activity

Combustible and Non-combustible Substances

HBSE 8th Class Science Combustion and Flame Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Why do we need fuel?
Answer:
We need fuel to generate energy.

Question 2.
Name any three fuels.
Answer:
Coal, wood, LPG, kerosene, petrol.

Question 3.
What is produced during combustion?
Answer:
Heat and light.

Question 4.
In what forms light is given during combustion?
Answer:
In form of flame or glow.

Question 5.
How does charcoal burn?
Answer:
It burns with glow.

Question 6.
How does a candle burn?
Answer:
It burns with flame.

Question 7.
Name two objects which burn without flame.
Answer:
Coal and charcoal.

Question 8.
Name two objects which burn with flame.
Answer:
LPG and candle.

Question 9.
Name any three combustible substances.
Answer:
Wood, coal, LPG.

Question 10.
What is necessary for substances to burn?
Answer:
Air.

Question 11.
How does sun produces heat although it does not have air?
Answer:
It produces heat by nuclear reactions.

Question 12.
In addition to air, what else is a necessary condition for a substance to burn?
Answer:
Low ignition temperature.

Question 13.
What are the substances with very low ignition temperature called?
Answer:
Inflammable substances.

Question 14.
Name some inflammable substances.
Answer:
Alcohol, petrol, LPG., etc.

Question 15.
What substances are used to extinguish fire?
Answer:
Water, sand, fire extinguishers.

Question 16.
What should we use to extinguish fire in case of electric short circuit?
Answer:
Sand or soil.

Question 17.
Name different types of fire extinguishers.
Answer:
(i) Soda-acid fire extinguishers
(ii) Hydrocarbon fire extinguisher.

Question 18.
Name different types of combustions.
Answer:
Rapid combustion, Spontaneous combustion and explosions.

Question 19.
Name different zones of a flame.
Answer:
Outer non-luminous zone, luminous zone and dark zone.

Question 20.
Which zone of a flame has highest temperature?
Answer:
Non-luminous zone.

Question 21.
Name two properties of an ideal fuel.
Answer:
High calorific value and low cost.

Question 22.
Is there any ideal fuel?
Answer:
No ideal fuel exist.

Question 23.
What is smoke?
Answer:
Smoke is unburnt carbon particles.

Question 24.
Which diseases do incomplete combustion cause?
Answer:
Respiratory and skin diseases.

Question 25.
What is supposed to be the cause of global warming?
Answer:
Increasing amount of carbon dioxide.

Question 26.
What is the rise in temperature of the environment of earth called?
Answer:
Global warming.

Question 27.
What does global warming lead to?
Answer:
Global warming leads to melting of polar glaciers.

Question 28.
Which chemicals give rise to acid rains?
Answer:
Sulphur dioxide and nitrogen oxides.

Question 29.
Which fuel is being used in automobiles in place of petrol and diesel?
Answer:
CNG.

Question 30.
Does CNG produce poisonous substances on burning?
Answer:
In very small amounts.

Short Answer Type Questions

Question 1.
Define combustion.
Answer:
A chemical process in which a substance reacts with oxygen to give off heat is called combustion. Burning of substances to get heat is called combustion.

Question 2.
What is produced when a combustible substance burns?
Answer:
When a combustible substance burns it produces heat and light. Light is in the form of glow or flame. Some combustible substances do not
burn in a flame, they simply glow.

Question 3.
How will you prove that air is necessary for burning?
Answer:
Burn a candle. Now put a beaker inverted on it. You will see the flame will flicker and then it will extinguish. As the inverted beaker has cut off the oxygen supply, the flame is extinguished. This proves air is necessary for burning.

Question 4.
What do you mean by ignition temperature?
Answer:
The lowest temperature at which a substance catches fire is called its ignition temperature. This is the temperature which has to be there, if the substance has to burn, below it the object will not catch fire.

Question 5.
What are inflammable substances?
Answer:
Some substances have very low ignition temperature and they catch fire very easily. Suflj substances are called inflammable substances. Petrol, alcohol, LPG etc. are the inflammable substances.

Question 6.
Write three things necessary for fire to produce?
Answer:
Three conditions necessary to produce fire are following:
(i) Presence of oxygen i.e, air.
(ii) Ignition temperature.
(iii) Presence of combustible substances.

Question 7.
What can be done to put the fire off?
Answer:
To put off the fire one of the conditions necessary for burning should be removed or controlled. If we cut off the supply of air, fire will be extinguished or we can bring the ignition temperature down to blow off the fire.

Question 8.
Why can’t water control the fire due to oils?
Answer:
Water cannot put off fire due to oils because water is lighter than oil. It settles down the oil particles and cannot bring the ignition temperature of the substance down, thus cannot control the fire.

Question 9.
What should be done to control fire due to oils?
Answer:
In case of fire due to oils, water is not useful as it is lighter than oil and settles down below the oil particles. In such cases, sand or soil should be used. They cut off the supply of air to the fire and it is put off.

Question 10.
How does carbondioxide help in putting off fire?
Answer:
Carbondioxide covers the surface of the burning substance and does not allow the oxygen to reach the substance. In absence of oxygen the fire gets put off.

Question 11.
What is rapid combustion?
Answer:
When gases bum quickly to produce heat and light it is called rapid combustion. This process takes place rapidly and takes less time.

Question 12.
What is spontaneous combustion?
Answer:
When an object catches fire on its own without any apparant cause, it is called spontaneous combustion. In this type of combustion the object suddenly bursts into flame. For example, phosphorus catches fire in air.

Question 13.
Write the properties of an ideal fuel.
Answer:
An ideal fuel has following qualities:
(i) It has high calorific value.
(ii) It has low ignition temperature.
(iii) It is cheap and easily available.
(iv) It can be easily transported.

Question 14.
Write some harmful effects of burning fuel.
Answer:
Burning fuel can cause following ill effects:
(i) Unbumt carbon particles of these fuels can cause respiratory and skin diseases.
(ii) Smoke emitted by these fuels cause pollution and many diseases.
(iii) Poisonous gases like carbondioxide, carbonmonoxide and sulphurdioxide etc. pollute the air.

Long Answer Type Questions

Question 1.
Explain the conditions necessary for cpmbustion.
Answer:
Combustion is burning of substances. For combustion of substances following conditions are necessary: .
(i) Air:
Substances only bum in sufficient supply of air i.e. oxygen. If the supply of air is hindered the object will not bum. In case of a burning object, if air is hindered, it will stop burning. This fact is used in extinguishing the fires.

(ii) Ignition Temperature:
Ignition temperature is the minimum temperature at which a substance starts burning. Those substances which have low ignition temperature can bum easily, while those which have high ignition temperature need more heating and burn late.

(iii) Presence of combustible substance:
If a substance is not combustible, it will not catch fire at all, so to produce fire it is necessary to have a combustible substance.

Question 2.
Describe the working of soda-acid fire extinguisher.
Answer:
Soda-acid fire extinguisher is based on the cooling the temperature of the burning object. This type of fire extinguisher contains sulphuric acid and sodium bicarbonate. When the extinguisher becomes functional, the sulphuric acid reacts with sodium bicarbonate to produce carbondioxide. Carbondioxide when released, cuts off the supply of oxygen and water is released to bring down the ignition temperature of the burning object. In this way fire is controlled.

Question 3.
What are different types of combustion?
Answer:
Combustion is of three types:
(i) Rapid combustion: When gases bum rapidly to produce heat and light it is called rapid combustion.
(ii) Spontaneous combustion: When any material like phosphorus bums on its own without any apparant cause, it is called spontaneous combustion.

(iii) Explosion:
When combustion takes place with sudden release of heat and light and a large amount of gas in form of bang, it is called explosion as in case of crackers and bombs.

Question 4.
Explain various harmful effects of burning fuels.
Answer:
Fuels are very useful for us. But there are certain disadvantages of burning fuels.
(i) Fuels like wood, coal, petroleum etc. which are carbon fuels generally release unbumt carbon particles which are quite harmful. They cause various respiratory and skin diseases.

(ii) In most of the cases carbondioxide is released during burning of fuels. This carbondioxide is released in environment. Carbondioxide is an identified cause of increasing temperature of the earth, which is called global warming.

(iii) Incomplete combustion of fuels release many poisonous gases like carbonmonoxide. in the environment. These poisonous gases create air pollution, such air if inhaled can be fatal.

(iv) Combustion of coal and diesel generates sulphurdioxide. It is a corrosive gas and it causes suffocation.

(v) Burning of petrol releases nitrogen oxides. These oxides of nitrogen and sulphurdioxide combine with rain water to cause acid rains.

Question 5.
Describe the various zones of a candle flame.
Answer:
The candle flame has three different zones. These zones can be distinguished on the basis of their colour.
(i) The outer zone:
It is blue in colour and it has very high temperature. It is the hottest zone of the flame. In this zones the wax vapours bum completely due to availability of enough oxygen, in turn carbondioxide and water vapours are produced.

(ii) The middle zone:
In this zone the flame bums with yellow colour and the wax vapours start burning here. The yellowish colour of the flame is due to the burning of carbon particles. These carbon particles are produced due te incomplete burning of the wax vapours due to less suppy of oxygen. Carbonmonoxide is also produced along the carbon particles. This zone is luminious but with low temperature.

(iii) The inner zone:
This zone appears black in colour as no combustion of wax vapour take place in this zone due to no supply of oxygen in this zone. It is the coolest zone of the flame having unbumt wax vapour.

Combustion and Flame Class 8 HBSE Notes

1. All substances which catch fire/bum in air are called combustible substances.
2. Wood, paper, petrol, L.P.G., charcoal etc. are some examples of combustible substances.
3. During combustion heat and light is emitted. The light is emitted in the form of flame.
4. All combustible substances do not burn with flame, for example coal does not bum with flame, while wood, paper, candle, L.P.G., etc. bum with a flame.
5. There are two main things required by a substance to become combustible. These are: low ignition temperature and air.
6. Ignition temperature is the lowest temperature at which a combustible substance can easily catch fire. Inflammable substances have very low ignition temperature.
7. If any of the above condition is removed,’fire can be extinguished. Either we bring ignition temperature below minimum or we cut off the supply of air.
8. Water, sand are mostly used to bring fire under control.
9. There are three main zones of a flame. The outermost zone has the highest temperature while the inner zone has unbumt carbon particles.
10. Fuel is a substance which is used to give energy and heat. Ideal fuel has low ignition temperature and readily available. It is cheap and has high calorific value. It is free from pollution.
11. But no fuel is an ideal fuel.
12. Fuels are not same in their efficiency and cost.
13. Calorific value of fuels is expressed in units of kilojouls per kg.
14. Combustion of an inflammable substance should be complete because incomplete combustion produce unburnt carbon particle which can cause serious environmental hazards like acid rain, global warming and poisonous gases causing dangerous diseases in living beings.
15. Global warming the most alarming environmental problem is being created due to increased amount of carbondioxide in air.
16. Acidic rain is caused due to the oxides of nitrogen and sulphur released in environment due to burning of coal, diesel and petrol.

Haryana State Board HBSE 8th Class Science Solutions Chapter 5 Coal and Petroleum Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 5 Coal and Petroleum

HBSE 8th Class Science Coal and Petroleum Textbook Questions and Answers

Question 1.
What are the advantages of using GNG and LPG as fuels?
Answer:
CNG – Compressed Natural Gas and LPG – Liquefied Petroleum Gas are easy to handle and use. It is easy to transport them and moreover they are free from any types of pollution on usage.

Question 2.
Name the petroleum product used for surfacing of roads?
Answer:
Bitumen or coaltar is used for surfacing of roads.

Question 3.
Describe how coal is formed from dead vegetation. What is this process called?
Answer:
Millions of years ago many dead animals and plants got trapped under the layers of earth. They got compressed and the temperature under the earth started raising due to hfgh pressure and temperature, the dead plants and animals got converted into coal. This process is called carbonization.

Question 4.
Fill in the blanks:
(а) Fossil fuels are ………. , …………. and …………. .
(b) On destructive distillation of coal …………. , …………. and …………. are obtained.
(c) Process of separation of different constituents from petroleum is called …………. .
(d) Least polluting fuel for vehicle is …………. .
Answer:
(a) coal, petroleum and natural gas
(b) coke, coal-tar and coal gas
(c) refining
(d) CNG.

Question 5.
Tick True/Ffdse against the following statements:
(а) Fossil fuels can be made in the laboratory. (T/F)
(b) CNG is more polluting fuel than petrol. (T/F)
(c) Coke is almost pure form of carbon. (T/F)
(d) Coal-tar is a mixture of various substances. (T/F)
(e) Kerosene is not a fossil fuel. (T/F)
Answer:
(a) False
(b) False
(c) True
(d) True
(e) False.

Question 6.
Explain why fossil fuels are exhaustible natural resources?
Answer:
Fossil fuels are exhaustible natural resources because they are made by the decomposition of the dead remains of living organisms. It is present in limited quantity beneath the earth, thus it will come to an end by human usage.

Question 7.
Describe characteristics and uses of coke.
Answer:
Coke is obtained by burning of coal in absence of oxygen. The process is called destructive distillation. Coke is used to manufacture steel. Coke is used in the extraction of many metals.

Question 8.
Explain the process of formation of petroleum.
Answer:
Petroleum is a fossil fuel. It is formed beneath the earth by decomposition of the dead bodies of the living organisms hurried beneath the earth. Due to some natural calamities like earthquake or volcano, innumerable living organisms (Plants and animals) got hurried beneath the earth. Due to heat and pressure, they started getting decomposed and got converted into liquid and gas form. In this way Petroleum oil and petroleum gas are formed.

Question 9.
The following Table shows the total power shortage in India from 1991-1997. Show the data in the form of a graph. Plot shortage percentage for the year on the Y- axis and the year on the X-axis.

Answer:

Extended Learning – Activities And Projects

Get an outline map of India. Mark the places in the map where coal, petroleum and natural gas are found. Show the places where petroleum refineries are situated.
Answer:
For self attempt.

2. Choose any five families of your neighbourhood. Enquire whether their energy consumption (coal, gas, electricity, petrol, kerosene) has increased or decreased in the last five years. Enquire also about the measures they adopt to conserve energy.
Answer:
For self attempt.

3. Find out the location of major thermal power plants in India. What could be the reasonsi for their being located at those places?
For more information visit:

• www.energyquest.ca.gov/story/chapter08.html
• en.wikipedia.org/ wiki/ Non-renewable_resources
• http://www.eiadoe.gov/kids/energyfacts/ sources/non-renewable/oil.html

Answer:
For self attempt.

HBSE 8th Class Science Coal and Petroleum Important Questions and Answers

Very Short Answer Type Questions

Question 1.
From where we find all the materials we use in our daily life?
Answer:
We get all these materials from natural resources as well as from man-made resources.

Question 2.
How many kinds of natural resources are there on the basis of availability of materials?
Answer:
On the basis of availability of materials, natural resources are oftwo types: Inexhaustible and exhaustible.

Question 3.
What are inexhaustible natural resources?
Answer:
Inexhaustible natural resources are those resources which cannot be finished by human activities.

Question 4.
Give two examples Pf Inexhaustible natural resources.
Answer:
Sunlight and air.

Question 5.
What are exhaustible natural resources?
Answer:
Exhaustible natural resources are those resources which are present in limited quantity and can get finished by hurt!an activities.

Question 6.
Give two examples of exhaustible natural resources.
Answer:
Petroleum, wildlife.

Question 7.
What are fossil fuels?
Answer:
Those fuels which got formed by the decomposition of the dead remains of living organisms for a long period of time are called fossil fuels.

Question 8.
Give tWo examples .of fossil fuel.
Answer:
Petroleum, coal.

Question 9.
What is coal?
Answer:
Coal is an exhaustible natural fossil fuel which is as hard as stone and is of black colour.

Question 10.
Write any two uses of coal.
Answer:
Coal is used as fuel to cook food. Coal is used as fuel to run trains.

Question 11.
What does coal mainly consist of?
Answer:
Coal mainly consists of carbon.

Question 12.
What is cabonization?
Answer:
Slow process of conversion of dead remains of living organisms into coal is called carbonization.

Question 13.
Which gas is released when coal ishumt?
Answer:
Carbondioxide.

Question 14.
To which process coal is put to get some useful products?
Answer:
Destructive distillation.

Question 15.
What is destructive distillation?
Answer:
Burning of coal in absence of oxygen to get coke and; other useful products is called destructive distillation.

Question 16.
What is the pure form of carbon?
Answer:
Coke.

Question 17.
What is coal-tar?
Answer:
Coal-tar is a black liquid that is produced during destructive distillation of coal.

Question 18.
Which petroleum product is used for metalling the roads in place of coal-tar?
Answer:
Bitumen.

Question 19.
What is used as fuel in light vehicles?
Answer:
Petrol.

Question 20.
What is used as fuel in heavy vehicles?
Answer:
Diesel.

Question 21.
Where was petroleum formed?
Answer:
Petroleum was formed under the sea.

Question 22.
Which conditions under the sea formed petroleum?
Answer:
Absence of air, high temperature and high pressure.

Question 23.
Where was the first oil well digged?
Answer:
Pennsylvania, U.S.A. in year 1859.

Question 24.
Name some places of India where oil is found.
Answer:
Assam, Gujarat, Bombay High, River basins of Godawari and Kaveri.

Question 25.
Which constituents are separated from-petroleum during its refining?
Answer:
Petroleum gas, petrol, diesel, lubricating oil, paraffin wax etc.

Question 26.
What is the full form of L.P.G.?
Answer:
Liquefied Petroleum Gas,

Question 27.
What is the use of L.P.G.?
Answer:
L.P.G. is used as fuel in home and in vehicles.

Question 28.
What is the use of Paraffin wax?
Answer:
Used in ointments, candles, vaseline, etc.

Question 29.
What are petrochemicals?
Answer:
Various useful constituents obtained from petroleum are called petrochemicals.

Question 30.
What is full form of C.N.G.?
Answer:
Compressed Natural Gas.

Question 31.
What are the uses of C.N.G.?
Answer:
C.N.G. is used as pollution free fuel for vehicles and in power generation.

Question 32.
Where in India is C.N.G. found?
Answer:
Tripura, Jaisalmer, Offshore of Mumbai and in Krishna Godawari Delta.

Question 33.
Can coal, petroleum and natural gas be prepared in laboratory?
Answer:
No.

Short Answer Type Questions

Question 1.
In how many types can we classify our resources?
Answer:
We can classify out natural resources in two types:
(i) Man-made resources
(ii) Natural resources.
Natural resources can further be classified in two types on the basis of the availability of resources: Exhaustible and inexhaustible resources.

Question 2.
What do you mean by Inexhaustible natural resources?
Answer:
These are the resources which are present in nature in unlimited amount and can never get finished by human activities. Air, sunlight, soil etc. are examples of inexhaustible natural resources.

Question 3.
What do you mean by exhaustible natural resources?
Answer:
Exhaustible natural resources are those resources which are present in nature in limited amounts and can get finished by human activities. Petroleum, Natural Gas, Coal etc. are exhaustible natural resources.

Question 4.
What do you mean by fossil fuels?
Answer:
Fuels which were formed by the dead remains of the living organisms by process which took thousands of year to complete are called fossil fuels. Petroleum, coal, natural gas are the fossil fuels which got formed under the sea and earth respectively, when they got hurried under the sea and earth.

Question 5.
What is coal and write its uses?
Answer:
Coal is a black stone like substance. It is formed by the dead remains of the living organisms.
(i) Coal is used as fuel to cook food.
(ii) It is used to run trains, as it is burnt to generate steam in engine.
(iii) It is used in thermal power plants to produce electricity.
(iv) Coal is also used as fuel in different industries.

Question 6.
How was coal formed?
Answer:
Millions of years ago dense forests of earth got hurried under the soil due to volcanoes and earthquakes. More deposits of soil compressed the hurried dead bodies. As they became deeper temperature started rising. This started converting dead bodies into coal.

Question 7.
What is coke? How is it useful to us?
Answer:
Coke is a hard porous black substance. It is obtained by destructive distillation of coke. It is almost pure form of carbon.
(i) Coke is used to manufacture steel.
(ii) It is used in extraction of many metals.

Question 8.
What is coal-tar? How is it useful to us?
Answer:
Black liquid obtained during destructive distillation of coal is coal-tar. It is thick and smells unpleasant. It is a mixture of hundreds of substances. Substances obtained from coal-tar are used to manufacture synthetic dyes, drugs, explosives, perfumes, plastics, paints, roofing materials, photographic materials, etc.

Question 9.
What do you mean by petroleum?
Answer:
Petroleum is a fossil fuel obtained from the dead remains of organisms living in sea. Petroleum is a dark oily liquid having unpleasant . odour. It has various useful constituents which are separated from it by process of fractional distillation at petroleum refineries.

Question 10.
How was petroleum lormed?
Answer:
Millions of years ago, sea organisms died and their dead bodies got settled at the bottom of the sea. Slowly they got covered by sand and clay. Absence of air, high temperature and high pressure for years, converted these bodies into petroleum oil and natural gas.

Question 11.
Name any three constituents obtained from refining petroleum and their uses.
Answer:
(i) L.P.G.: It is used as domestic fuel and fuel for vehicles.
(ii) Petrol: It is used as fuel for light vehicles, aviation fuel and used in drycleaning of fabric.
(iii) Kerosene: It is used as fuel for stoves, lamps an d for jet aircrafts.

Question 12.
What is diesel? How is it different from petrol?
Answer:
Diesel is one of the constituents obtained by the refining or fractional distillation of petroleum. It is mainly used as the fuel for vehicles as petrol is used. But it is different from petrol, as it is used as fuel for heavy vehicles like trucks, lories, etc. while petrol is used as fuel in light vehicles like cars, scooters, etc.

Question 13.
What is CNG?
Answer:
GNG is Compressed Natural Gas which is a fossil fuel and is formed along petroleum oil. It is used as the pollution free fuel for transport vehicles. It is more convinient to use as its transportation is easy and it can be directly burnt.

Long Answer Type Questions

Question 1.
Classify various materials we use in our lives.
Answer:
All the materials we use can be broadly classified into two groups:
(a) Natural Resources
(b) Man-made Resources.
(a) Natural resources are those resources which are present in our nature, gifted by God. They can be freely used. Soil, air, sunlight, water, wildlife, etc. are some natural resources.
(b) Man-made resources are those resources which are formed by various efforts of man and are artificial. Plastics, fibres, electricity, etc. are all artificial resources.

On availability of materials natural materials can further be classified as:
(i) Inexhaustible Natural Resources:
Those resources which are present in unlimited quantity and will never get exhausted by human activities. Sunlight, air, soil, etc. are some inexhaustible natural resources.

(ii) Exhaustible Natural Resources:
Those resources which are available in limited amount and will get finished by human activities. Petroleum, coal, wildlife, forests, etc. are some examples of exhaustible natural resources.

Question 2.
What is coal and how was it formed? Explain.
Answer:
Coal is a fossil fuel which is as hard as a stone. It is black in colour and is mainly used as fuel. As coal is a fossil fuel, it was formed by the dead remains of the plants. Millions of years ago vegetation in forests got trapped under soil layers due to earthquakes and volcanic erruptions. More soil layers got deposited on it and it went deeper and deeper beneath the earth.

This raised the temperature and pressure beneath the soil. This initiated the process of burning these dead remains. Slowly all the vegetations got converted into coal which is a rich form of carbon. This whole process is also called carbonization.

Question 3.
How was petroleum formed? What is refining of petroleum?
Answer:
Petroleum is a fossil fuel which got formed by the dead remains of the sea-animals. These animals slowly got trapped under soil and clay and more deposits were formed with time. Due to depth, the temperature and pressure raised and over the years they got converted into petroleum oil. Since oil is lighter than water, it did not get mix with water and got raised to the superficial rocks, which did not allow it to pass through them. To obtain petroleum, we have to dig wells to perforate the top rocks and pump up the petroleum oil.

The petroleum oil we get from these wells is a mixture of variuos other useful substances. Petroleum oil is, thus, refined to separate these useful by-products in petroleum refineries.

Question 4.
Name different constituents of petroleum and write their uses.
Answer:
Following are various constituents of petroleum oil obtained during fractional distillation in oil refineries:
(i) Liquefied Petroleum Gas (L.P.G.): It is primarily used as domestic fuel. Now it is used as fuel in vehicles and industry.
(ii) Petrol: It is a black liquid used as fuel in light vehicles like scooters, cars, etc. It is also used as aviation fuel and used for dry cleaning of fabrics.
(iii) Kerosene: It is used as fuel in stoves, lamps and jet aircrafts.
(iv) Diesel: It is used as fuel for heavy vehicles and in electric generators.
(v) Lubricating oil: It, is used to lubricate metal parts and machines.
(vi) Paraffin wax: It is used in ointments’, vaselines and in candles.
(vii) Bitumen: It is used in paints and is used in road-surfacing in place of coal-tar.

Question 5.
Write a note on Natural Gas.
Answer:
Natural gas is one of the most important forms of fossil fuel. The reason being that it is very easy to transport through pipes and cylinders. Natural gas is extracted and stored under very high pressure. As it is kept compressed under high pressure, it is called .

Compressed Natural Gas or CNG. The great advantage of CNG is that it does not cause pollution on usage as in case of other petrochemicals like petrol and diesel. Secondly, it can be directly burnt in homes and factories for cooking and other purposes. Natural gas is also used as the fuel for many manufacturing units of chemicals and fertilizers.

Question 6.
Why is it necessary to use coal and petroleum economically?
Answer:
There are two main reasons for which economical use of fossil fuels is necessary.
(i) Fossil fuels are exhaustible sources. If they are used indiscriminately, they will be exhausted, as they are present in nature in limited amount. It takes millions of years to form fossil fuels, so it is not possible to make new fossil fuels artificially.

(ii) Secondly, fossil fuels specially coke, petrol, diesel, etc. generate polluting gases on burning. Coke is almost carbon and produces carbondioxide on binning, whieh pollutes our environment. These polluting emissions have given rise to dangers of global warming and air pollution. So, their limited and economic use can control pollution and give better environment to live in.

Question 7.
Write some ways in which we can conserve fossil fuels.
Answer:
Economic and controlled consumption of fossil fuel can help conserving our natural resources. Following ways and measures can conserve owr resources:
(i) Vehicles shcaiM be driven at eeaastant and moderate speed.
(ii) Engines should he switched off at traffic lights or other temporary halts.
(iii) Proper and regular maintenance of vehicles.
(iv) Vehicle pooling can reduce number of vehicles plying on road thus less consumption of fuel.
(v) At home gas stoves should he cleaned properly and burners should not he left boring unnecessarily.
(vi) Pressure cookers should be preferred to pans. If pans are being used, they should he properly covered and their bottoms should not have deposits of burnt oil.
(vii) Small pans and burners should be used and pulses etc. should be dipped in water before cooking them.

Coal and Petroleum Class 8 HBSE Notes

1. We get various materials from various sources. These sources cam be natural or man-made. Natural resources are like air, water, soil, minerals, etc.
2. Natural resources are of two types according to their availability
(a) Inexhaustible
(b) Exhaustible.
3. Inexhaustible resources are those which are unlimited and are not supposed to come to an end by human use e.g. air is in exhaustible resource.
4. Exhaustible resourcs are those resources which are present in limited quantity and which can come to an end by human use e.g. forests, coal, petroleum, wildlife and natural gas, minerals, etc.
5. Coal, petroleum, natural gas etc. are called fossil fuels because they are formed by the decomposition of the dead bodies of plants and animals.
6. These fossil fuels are used by humans for their various energy requirements.
7. Coal was formed under the earth about 300 million years ago. The de forests of the earth got hurried under soil due to earthquakes and volcanic erruptions. The compressed under the layers of soil. Rising temperature under the earth converted these dead bodies into coal. Coal mainly consists of carbon.
8. The whole process of conversion of dead bodies of plants and animals into coal is called carbonization.
9. Heating of coal in absence oT cur to form coke is called destructive distillation. Destructive distillation is the process which produces various petroleum products like coaltar, coal-gas, etc.
10. Petroleum is refined to get various by-products like petrol, petroleum gas, paraffin wax, diesel, lubricating oil, etc.
11. All these resources of energy are present in limited quantity. It was a long process which took place to convert dead bodies of living beiqgs to get converted into petroleum products. So they will get exhausted if used indiscriminately.

Haryana State Board HBSE 8th Class Science Solutions Chapter 14 Chemical Effects of Electric Current Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 14 Chemical Effects of Electric Current

HBSE 8th Class Science Chemical Effects of Electric Current Textbook Questions and Answers

Question 1.
Fill in the blanks:
(а) Most liquids that conduct electricity are solutions of __________ and __________.
(b) The passage of an electric current through a solution causes __________ effect.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the __________ terfninal of the battery.
(d) The process of depositing a layer of any desired metal on another metafile object, by means of electricity, is called __________.
Answer:
(a) acids and bases
(b) chemical
(c) negative
(d) electroplating

Question 2.
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection, dan yon explain the
Answer:
Yes, the solution is a good conductor of electricity. The reason is that tote solution is a good conductor of electricity, so the needle get deflected.

Question 3.
Name three liquids, which when tested in the manner shown in figure, may cause the magnetic needle to direct.
Answer:
Tap water, lime water, vinegar.

Question 4.
The bulb does not glow in the setup shewn in figure. List the possible reasons. Explain your answer.
Answer:
If the bulb does not glow it may be because of some reasons like the bulb may be fused. Replaced with a new bulb, if it still does not glow, it shows that the connection of wires may be loose. After tightening connetions if still the bulb does not glow, then it is for sure that the solution does not conduct electric current.

Question 5.
A tester is used to check the conduction of electricity through two liquids, labeled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that
(i) liquid A is a better conductor than liquid B.
(ii) liquid Bis a better conductor than liquid
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.
Answer:
(ii) liquid A is a better conductor than liquid B.

Question 6.
Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer:
Some salt can be added to it to make it a conductor.

Question 7.
In case of fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.
Answer:
Water is a good conductor of electric current. So, the firemen shut off the electric supply before spraying water to save themselves and other people from electrocution.

Question 8.
A child staying in the coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Answer:
Drinking water has been processed and purified before supplying it to the houses. Many salts and minerals have been removed from it, so it has decreased its conductivity. On the other hand the sea water is rich in salts, and other acids and basic substances, that is why it is a better conductor of electricity and deflects the needle more than the purified drinking water.

Question 9.
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Answer:
No, it is highly dangerous to carry on electric repairs in water, as water is a good conductor of electricity. It can cause electrocution.

Question 10.
Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?
Answer:
While it rains, the raindrops get mixed with the suspended particles of the air. So, they do not remain pure. It becomes the mixture of salts and other impurities thus shows conduction of electricity.

Question 11.
Prepare a list of objects around you that are electroplated.
Answer:
Following objects around us are electroplated, rims of cycles, door handles, taps, showers, metallic pens, artificial jewellery, utensils, metallic almirahs, buckles of clothes and belts etc.

Question 12.
The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transfered to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Answer:
The impure copper rod should be attached to the positive terminal because the free copper will get drawn towards the negative terminal to be get deposted, so the copper from impure rod will get collected in the pure copper plate.

Extended Learning – Activities and Projects

Question 1.
Test the conduction of electricity through various fruits and vegetables. Display your result in a tabular form.
Answer:
For self attempt.

Question 2.
Repeat the Activity 14.7 with a zinc plate in place of the copper plate connected to the negative terminal of the battery. Now replace zinc plate with some other metallic object and again repeat the activity. Which metal gets deposited over which other metal? Discuss your findings with your friends.
Answer:
For self attempt.

Question 3.
Find out if there is a commercial electroplating unit in your town. What objects are electroplated there and for what purpose? (The process of electroplating in a commercial unit is much more complex than what we did in Activity 14.7). Find out how they dispose off the chemicals they discard.
Answer:
For self attempt.

Question 4.
Imagine that you are an ‘entrepreneur’ and have been provided a loan by a bank to set up a small electroplating unit. What object you would like to electroplate and for what purpose? (Look up the meaning of‘entrepreneur’ in a dictionary).
Answer:
For self attempt.

Question 5.
Find out the health concerns associated with chromium electroplating. How are people trying to resolve them?
Answer:
For self attempt.

Question 6.
You can make a fun pen for yourself. Take a conducting metal plate and spread a moist paste of Potassium Iodide and starch. Connect the plate to a battery as shown in Fig. 14.11. Now using the free end of the wire, write a few letters on the paste. What do you see?

For more information on this topic visit:
www.tutorvista.com/content/physies/phys- ics-iv/thermalchemical-currents/chemical-ef- fects-current.php
www.physchem.co.za/Redox/ Electrolysis.htm
electronics .howstuffworks.com/3 ed ,htm
Answer:
For self attempt.

HBSE 7th Class Science Chemical Effects of Electric Current Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is electric current?
Answer:
Flow of electrons is called current.

Question 2.
How can we check current?
Answer:
By using a tester.

Question 3.
What are conductors?
Answer:
Substances which allow the electric current to pass through them are called conductors.

Question 4.
What are insulators?
Answer:
Substances which do not allow electric current to pass through them are called insulators.

Question 5.
Name any conductor.
Answer:
Copper.

Question 6.
Name any insulator.
Answer:
Plsatic.

Question 7.
Are liquids conductor of electricity?
Answer:
Yes, some liquids are conductors of electricity.

Question 8.
Name any liquid conductor.
Answer:
Tap water.

Question 9.
Can distilled water conduct electricity?
Answer:
No.

Question 10.
How can distilled water be made conductor of electricity?
Answer:
By adding some salt to it.

Question 11.
How can we check magnetic effects of electric current?
Answer:
By using magnetic compass.

Question 12.
How does magnetic compass show magnetic effect?
Answer:
By deflection.

Question 13.
What makes most of the liquids good conductors of electricity?
Answer:
Acids, bases and salts.

Question 14.
Name any two liquids except water which conduct electricity.
Answer:
Vinegar and lemon juice.

Question 15.
What is an electric circuit?
Answer:
Path of the flow of electric current is called electric circuit.

Question 16.
What in a electric circuit shows that current is passing through it?
Answer:
Glowing bulb.

Question 17.
Will a bulb glow when circuit is completed in an insulating solution?
Answer:
No.

Question 18.
Which effect of electric current causes the bulb, to glow?
Answer:
Heating effect.

Question 19.
What glows in a bulb?
Answer:
Filament

Question 20.
What is LED?
Answer:
LED is like a bulb which even glows at low or a small current.

Question 21.
What is full form of LED?
Answer:
Light Emitting Diode.

Question 22.
What are the better sources of light than bulbs and tubes?
Answer:
C.F.L.

Question 23.
What is used in CFLs?
Answer:
Mercury.

Question 24.
What other object can be used in place of bulbs to see the flow of electric current?
Answer:
Magnetic Compass.

Question 25.
What are the metal rods dipped in liquids to which cells are attached called?
Answer:
Electrodes.

Question 26.
What are the bubbles seen near electrodes after passing current through a conducting solution?
Answer:
Hydrogen and Oxygen gas.

Question 27.
When we pass current through a conducting solution of water, which gas bubbles will appear near positively charged electrode?
Answer:
Oxygen.

Question 28.
Which gas will accumulate near negative electrode when electric current is passed through a conducting solution of water?
Answer:
Hydrogen.

Question 29.
Name any chemical effect of electric current.
Answer:
Electroplating.

Question 30.
What is electroplating?
Answer:
Coating of a desired metal oft other metallic surface using electric current is Called electroplating.

Question 31.
To which terminal of the battery the metal meant for electroplating is attached?
Answer:
Negative terminal.

Question 32.
Which metal is plated on handlebars of cycles and rims of wheels?
Answer:
Chromium.

Question 33.
Which metal is plated on the iron to protect it from mist and corrosion, which is used in building bridges? .
Answer:
line.

Question 34.
Is air an insulator or conductor?
Answer:
Insulator.

Question 35.
In which direction does current flow?
Answer:
Current flows from negative terminal to the positive terminal.

Short Answer Type Questions

Question 1.
What is an electric Current?
Answer:
Plow of electrons is called electric current. Negatively charged electrons flow from negative terminal to the positive terminal and this is called electric current and the path through which it flows is called electric circuit.

Question 2.
What is a tester?
Answer:
Tester is an instrument which is Used to check the flow of electric current. It is attached to the terminal of the electric circuit, if the bulb attached to tester glows, it confirms the passage of current.

Question 3.
What are conductors?
Answer:
Substances which allow the electric current to pass through them are called conductors. Substances through which electric current passes easily are called good conductors and substances through which current passes partially or in small quantity they are called bad conductors. Substances like copper, iron, aluminium etc. are called conductors.

Question 4.
What are insulators?
Answer:
Substances which do not allow the electric current to pass through them are called insulators. Electric current do not pass through them and do not show any effect of electric current. Substances like wood, plastic, rubber* distilled water etc. are insulators.

Question 5.
Can electric current pass through liquids? Explain.
Or
Are liquids Conductor or insulator? Explain.
Answer:
Some liquids allow the electric current to pass through them and some liquids do not allow the electric current to pass through them. Mostly liquid conductors are solutions of acids, bases and salts. Liquids free from acids, bases and salts are insulators e.g. mineral water is pure form of water it is an insulator. Lemon juice vinegar are conductors.

Question 6.
You are given a solution containing lemon juice and salt.
You are told to check whether it is a conductor or insulator. How will you show it diagrammatically.
Answer:

Question 7.
You are given distilled water. Check if it is a conductor or insulator?
Answer:
Distilled water is taken in a Plastic container. The free ends of the tester are dipped in the container. After waiting for a few miniutes we will find that the bulb does not glow. It confirms that distilled water does not allow electric current to pass through it so it is an insulator.

Question 8.
What is magnetic effect of current?
Answer:
When current is passed through a coil it behaves like a strong permanent magnet. The strength of the magnet depends upon the current through the wire and number of turns of the coil. This coil will continue to behave like a magnet still the current passes through it.

Question 9.
Draw an electric circuit showing different components like a battery, conducting wire, bulb and free ends dipped in conducting solution.
Answer:

Question 10.
What is LED, why is it a most preferable source of light?
Answer:
LED means Light Emitting Diode. Ordinary bulbs do not glow when current is small. They need large supply of current to emit light. So, they consume more current, they thus prove to be costly. On the other hand LED can glow even at very small supply of electricity and consume small current. Thus it is economical.

Question 11.
Why does a bulb glow when electric current passes through it?
Answer:
When electric current passes through a bulb, the filament of the bulb starts heating up. This is called heating effect of current. The filament gets heated up to such a high temperature that it starts glowing.

Question 12.
How can we prove conduction of substances when current is very small and the bulb does not glow?
Answer:
When current passing through a conductor is very small, the bulb does not glow. In such case we use magnetic compass to know the conduction of current. Electric current has magnetic effect which deflects the magnetic compass proving that current is flowing around the compass.

Question 13.
Why do we need magnetic compass to test the conduction of electric current?
Answer:
Sometimes when we make to flow current through a conductor, the bulb does not glow. This is because the electric current flowing through conductor is so small, that the filament of the bulb does not get heated up to the temperature where it starts glowing. So, in case of small current we need magnetic compass to test the conduction. juice is mixed in distilled water it becomes conductor of electricity.

Long Answer Type Questions

Question 1.
What happens when we add a pinch of salt or some lemon juice in distilled water to test its conduction of electric current?
Answer:
Distilled water does not allow the electric current to pass through it. But when we add some salt or the lemon juice to it, it starts conducting electric current and shows deflection of magnetic compass because salts and acids are conductors of electric current when salt or lemon juice is mixed in distilled water it becomes conductor of electricity.

Question 2.
Why is it not advisable to touch any electrical appliance with wet hands?
Answer:
It is not advisable to touch electrical appliances with wet hands because it can send electric shock in our body. Water is conductor of electric current. It easily allows electric current to pass through it, so when we will touch the switch or electrical appliance with wet hands the water will alow the current to pass through it and electric current will reach our body giving us shocks. This can sometimes prove very dangerous even fatal.

Question 3.
What is Electroplating? How does it take place?
Answer:
Electroplating is the process of coating a desired metal on an undesired metal surface using electric current.

Metallic plate and the substance requiring coating are dipped in conducting solution with conducting wires. The object to be coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the conducting solution start breaking and free metallic particles get deposited on the object at negative terminal of battery. In this way we can get a coating of desired metal on any object by preparing suitable conducting solution and using suitable electrodes.

Question 4.
What are the advantages of electroplating?
Answer:
Electroplating has many advantages.

• It is used to coat metal surfaces with desired metal coatings.
• It saves metal surfaces from rusting
• It saves corrosion of surfaces of metals.
• Coating of chromium on metals give lustre to objects.
• Cheap metals like iron, aluminium etc. can be coated with costly metals like silver, gold etc. to give them rich look as in case of artificial jewellery.
• It can make reactive metals like iron etc. less reactive and they can be used for storing food items etc.

Question 5.
Show experimentally that a current carrying wire behaves like a magnet.
Answer:
As in figure shown below, a wire is fixed along the edge of a table. Place a magnetic compass near the wire. Connect the two ends of the wire to a battery cell. There is a deflection in the magnetic compass. Place the compass at different points on the table at varying distances from the wire. Observe the deflection in each case. We guess from this activity that a current carrying wire behaves like a magnet. When the current is stopped, the associated megnatic property also vanishes.

Question 6.
How can you prepare an electric pen?
Answer:
Take a filter paper and soak it into potassiumiodide and starch solution. Spread it on a metal sheet. Now join two connecting wires to the terminals of battery. Attach the wire

connected at positive end to plate. Now write on the sheet the wire attached to negative terminal. Wherever you will write blue coloured inck will appear. This happen due to electrolysis of potassium iodide solution which produces iodine. Iodine on reaction with starch produce ink of blue colour.

Chemical Effects of Electric Current Class 8 HBSE Notes

• Flow of electrons is called current.
• Those objects which allow the current to pass though them are called conductors.
• Those objects which do not allow the current to pass through them are called insulators.
• Objects like copper, aluminium etc. and almost all metals are good conductors of electricity.
• Objects like wood, plastic, rubber etc. do not allow electricity to pass through totem and are – thus bad conductors of electricity and are thus called insulators.
• liquids like’vinegar, lemon juice, tap water etc. are conductors of electricity and distilled water is an insulator. Salted distilled water becomes a conductor.
• Electric current has many chemical effects.
• Electric current when passed through a conducting solution causes different changes in it, these are called chemical changes.
• It may evolve gas after breaking the chemical solution into different elements. Chemical effects depend upon the conducting solution and the electrodes used.
• Electrodes are the rods of different metals immersed in conducting solution to complete the circuit and cause flow of electrons.
• Electric current when passed through a conducting solution can cause electroplating.
• Electroplating is the process of depositing layer of any suitable metal on another metal.