Class 8

Haryana State Board HBSE 8th Class Maths Solutions Chapter 6 वर्ग और वर्गमूल Intext Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 6 वर्ग और वर्गमूल Intext Questions

(प्रयास कीजिए – पृष्ठ 96)

प्रश्न 1.
दी गई संख्याओं के बीच की पूर्ण वर्ग संख्याएँ ज्ञात कीजिए-
(i) 30 और 40
(ii) 50 और 60
हल:
5 × 5 = 25, 6 × 6 = 36, 7 × 7 = 49 और 8 × 8 = 64
∴ 30 और 40 के बीच की पूर्ण संख्या 36 है।

(ii) 50 और 60 के बीच की पूर्ण वर्ग संख्या नहीं है।

पृष्ठ 97

प्रश्न 1.
क्या हम कह सकते हैं कि निम्न संख्याएँ पूर्ण वर्ग संख्याएँ हैं? हम कैसे जानते हैं?
(i) 1057
(ii) 23453
(iii) 7928
(iv) 222222
(v) 1069
(vi) 2061
पाँच ऐसी संख्याएँ लिखिए जिनके इकाई स्थान को देखकर आप बता सकें कि ये संख्याएँ वर्ग संख्याएँ नहीं हैं।

(i) 1057 – चूँकि इकाई स्थान का अंक 0, 1, 4, 5, 6 या 9 नहीं है। अतः यह पूर्ण वर्ग संख्या नहीं है।

(ii) 23453 – चूँकिे इकाई स्थान पर 0, 1, 4, 5, 6 या 9 नहीं है। अतः यह पूर्ण वर्ग संख्या नहीं है।

(iii) 7928 – चूँकि इकाई स्थान पर 0, 1, 4, 5, 6 या 9 नहीं है। अतः यह पूर्ण वर्ग संख्या नहीं हो सकती है।

(iv) 222222 – चूँकि इकाई के स्थान पर 0, 1, 4, 5, 6 या 9 नहीं है। अतः यह पूर्ण वर्ग संख्या नहीं हो सकती है।

(v) 1069 – चूँकि इकाई स्थान पर 9 है। अतः यह पूर्ण वर्ग संख्या हो सकती है और नहीं भी हो सकती है।
अब
32² = 32 × 32 = 1024
और 33² = 33 × 33 = 1089
अतः 1069 एक पूर्ण वर्ग संख्या नहीं है।

(vi) 2061 – इकाई के स्थान पर 1 है। अतः यह संख्या पूर्ण वर्ग संख्या भी हो सकती है और नहीं भी हो सकती है।
लेकिन 45² = 45 × 45 = 2025
और 46² = 46 × 46 = 2116
अतः 2061 एक पूर्ण वर्ग संख्या नहीं है।

पाँच संख्याएँ जिनके इकाई स्थान को देखकर हम पता कर सकते हैं कि ये वर्ग संख्याएँ नहीं हैं, वे हैं 22, 33, 47, 58 और 68.

प्रश्न 2.
पाँच ऐसी संख्याएँ लिखिए जिनके इकाई स्थान को देखकर आप नहीं बता सकते कि वे वर्ग संख्याएँ हैं या नहीं?
हल:
ऐसी पाँच संख्याएँ जिनके इकाई स्थान को देखकर हम नहीं बता सकते कि ये वर्ग संख्याएँ हैं या नहीं, वे हैं-
1000, 1001, 2004, 30015, 74566

(प्रयास कीजिए – पृष्ठ 97)

प्रश्न 1.
123²,77²,82², 161², 109² में से कौनसी संख्या अंक 1 पर समाप्त होगी?
हल:
यदि संख्या के इकाई संख्याएँ का अंक 1 और 9 है, तो इनके वर्ग 1 पर समाप्त होते हैं। अतः संख्याएँ 161² और 109² के अंक एक पर समाप्त होंगे।

(प्रयास कीजिए – पृष्ठ 98)

प्रश्न 1.
निम्नलिखित में से कौनसी संख्याओं के इकाई स्थान पर 6 अंक होगा
(i) 19²
(ii) 24²
(iii) 26²
(iv) 36²
(v) 34²
हल:
जिस संख्या का इकाई अंक 4 या 6 होता है, उस संख्या के वर्ग इकाई स्थान पर 6 अंक होता है।
अतः 24, 26, 36, तथा 34 के इकाई स्थान पर 6 आएगा।

(प्रयास कीजिए – पृष्ठ 98)

प्रश्न 1.
निम्नलिखित संख्याओं के वर्ग करने पर उनके इकाई स्थान पर क्या होगा?
(i) 1234
(ii) 26387
(iii) 52698
(iv) 99880
(v) 21222
(vi) 9106
हल:

क्र.सं.	संख्या	वर्ग करने पर उनके इकाई स्थान पर	संकेत
(i)	1234	6	4 × 4 = 16
(ii)	26387	9	7 × 7 = 49
(iii)	52698	4	8 × 8 = 64
(iv)	99880	0	0 × 0 = 0
(v)	21222	4	2 × 2 = 4
(vi)	9106	6	6 × 6 = 36

(प्रयास कीजिए – पृष्ठ 98)

प्रश्न 1.
निम्नलिखित में से किन संख्याओं के वर्ग विषम संख्या/सम संख्या होंगे? क्यों?
(i) 727
(ii) 158
(iii) 269
(iv) 1980
हल:
(i) 727 एक विषम संख्या है, इसलिए इसका वर्ग भी विषम संख्या होगी।
(ii) 158 एक सम संख्या है। इसलिए इसका वर्ग भी सम संख्या होगी।
(iii) 269 एक विषम संख्या है। इसलिए इसका वर्ग भी विषम संख्या होगी।
(iv) 1980 एक सम संख्या है। इसलिए इसका वर्ग भी सम संख्या होगी।

प्रश्न 2.
निम्नलिखित संख्याओं के वर्ग में शून्यों की संख्या क्या होगी?
(i) 60
(ii) 400
हल:
(i) 60 दो शून्य
(ii) 400 चार शून्य

(प्रयास कीजिए – पृष्ठ 100)

प्रश्न 1.
9² और 10² के बीच कितनी प्राकृत संख्याएँ हैं?
11² और 12² के बीच भी प्राकृत संख्याओं की संख्या बताइए।
हल:
9² और 10² के बीच प्राकृत संख्याएँ 2n होंगी, जबकि n = 9 होगा।
अतः 2 × 9 = 18 प्राकृत संख्याएँ हैं।

इसी प्रकार 11² और 12² के बीच 2 × 11 = 22 प्राकृत संख्याएँ हैं।

प्रश्न 2.
निम्नलिखित संख्याओं के यग्मों के बीच की संख्या बताइए जो वर्ग संख्याएँ नहीं हैं।
(i) 100² और 101²
(ii) 90² और 91²
(iii) 1000² और 1001²
हल:
(i) 100² और 101² के बीच 2n = 2 × 100 = 200 संख्याएँ हैं, जो वर्ग संख्याएँ नहीं हैं।

(ii) 90² और 91²के बीच 2n = 2 × 90 = 180 संख्याएँ हैं, जो वर्ग संख्याएँ नहीं हैं।

(iii) 1000² और 1001² के बीच 2n = 2 × 1000 = 2000 संख्याएँ हैं, जो वर्ग संख्याएँ नहीं हैं।

(प्रयास कीजिए – पृष्ठ 101)

प्रश्न 1.
निम्नलिखित संख्याओं में प्रत्येक पूर्ण वर्ग संख्याएँ हैं अथवा नहीं?
(i) 121
(ii) 55
(iii) 81
(iv) 49
(v) 69
हल:
(i) 121
पहली n विषम प्राकृत संख्याओं का योग n² होता है, चूंकि उक्त संख्याओं में से 1,3,5,7,9,……… को क्रम से घटाते हैं।
121 – 1 = 120, 120 – 3 = 117, 117 – 5 = 112, 112 – 7 = 105, 105 – 93 = 96, 96 – 11 = 85, 85 – 13 = 72, 72 – 15 = 57, 57 – 17 = 40, 40 –19 = 21, 21 – 21 = 0
अर्थात् यहाँ 121 = 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 + 21
अतः 121 एक पूर्ण वर्ग संख्या है।

(ii) 55
55 – 1 = 54, 54 – 3 = 51, 51 – 5 = 46, 46 – 7 = 39, 39 – 9 = 30, 30 – 11 = 19, 19 – 13 = 6, 6 – 6, 6 – 15 = -9
∵ 55 से 1 प्रारम्भ होने वाली विषम संख्याओं का योग नहीं है।
∴ 55 एक पूर्ण वर्ग संख्या नहीं है।।

(iii) 81
81 – 1 = 80, 80 – 3 = 77, 77 – 5 = 72, 72 – 7 = 65, 65 – 9 = 56, 56 – 11 = 45, 45 – 13 = 32, 32 – 15 = 17, 17 – 17 = 0
अर्थात् यहाँ 81 = 1+ 3 +5 +7+9+ 11+ 13 + 15 + 17
∴ 81 एक पूर्ण वर्ग संख्या है।

(iv) 49
49 – 1 = 48, 48 – 3 = 45, 45 – 5 = 40, 40 – 7 = 33, 33 – 9 = 24, 24 – 11 = 13, 13 – 13 = 0
अर्थात् यहाँ 49 = 1 + 3 + 5 + 7 + 9 + 11 + 13
∴ 49 एक पूर्ण वर्ग संख्या है।

(v) 69
69 – 1 = 68, 68 – 3 = 65, 65 – 5 = 60, 60 – 7 = 53, 53 – 9 = 44, 44 – 11 = 33, 33 – 13 = 20, 20 – 17 = 3, 3 – 1
∵ 69 से 1 प्रारम्भ होने वाली विषम संख्याओं का योग नहीं है।
∴ 69 एक पूर्ण वर्ग संख्या नहीं है।

(प्रयास कीजिए – पृष्ठ 101)

प्रश्न 1.
निम्नलिखित संख्याओं को दो क्रमागत पूर्णांकों के योग के रूप में लिखिए
(i) 21²
(ii) 13²
(iii) 11²
(iv) 19²
हल:

प्रश्न 2.
क्या आप सोचते हैं कि इसका विलोम सत्य है अर्थात् क्या दो क्रमागत धनात्मक पूर्णांकों का योग एक पूर्ण वर्ग होता है? अपने उत्तर के पक्ष में एक उदाहरण दीजिए।
हल:
दो क्रमागत धनात्मक पूर्णांकों का योग सदैव एक पूर्ण वर्ग नहीं होता है।
उदाहरण: 10 + 11 = 21
यहाँ 10 + 11 क्रमागत धनात्मक पूर्णांक हैं, परन्तु इनका योग पूर्ण वर्ग संख्याएँ नहीं है।

(प्रयास कीजिए – पृष्ठ 102)

प्रश्न 1.
निम्न प्रतिरूप का उपयोग करते हुए नीचे दी गई संख्याओं की वर्ग संख्याएँ लिखिए

(i) 111111²
(ii) 1111111²
हल:
(i) 111111² = 1 2 3 4 5 6 5 4 3 2 1
(ii) 1111111² = 1 2 3 4 5 6 7 6 5 4 3 2 1

प्रश्न 2.
दिए गए प्रतिरूप का उपयोग करते हुए क्या आप निम्नलिखित संख्याओं का वर्ग ज्ञात कर सकते हैं?
(i) 6666667²
(ii) 66666667²
प्रतिरूप-
7² = 49
67² = 4489
667² = 444889
6667² = 44448889
66667² = 4444488889
666667² = 444444888889
हल:
(i) 6666667² = 44444448888889
(ii) 66666667² = 4444444488888889

(प्रयास कीजिए – पृष्ठ 104)

प्रश्न 1.
निम्नलिखित संख्याओं के वर्ग ज्ञात कीजिए जिनके इकाई अंक 5 हैं
(i) 15
(ii) 95
(iii) 105
(iv) 205
हल:
(i) 15² = (1 × 2) सौकाई + 25
= 200 + 25 = 225

(ii) 95
95² = (9 × 10) सौकाई + 25
= 9000 + 25 = 9025

(iii) 105
105² = (10 × 11) सौकाई + 25.
= 11000 + 25 = 11025

(iv) 205
205² = (20 × 21) सौकाई + 25
= 42000 + 25 = 42025

(प्रयास कीजिए – पृष्ठ 106)

प्रश्न 1.
(i) 11² = 121, 121 का वर्गमल क्या है?
(ii) 14² = 196, 196 का वर्गमूल क्या है?
हल:
(i) 121 का वर्गमूल 11 है।
(ii) 196 का वर्गमूल 14 है।

(सोचिए, चर्चा कीजिए और लिखिए – पृष्ठ 106)

प्रश्न 1.
(-1)² = 1. क्या 1 का वर्गमूल है -1?
हल:
1 का वर्गमूल -1 तथा 1 होते है।
अत: 1 का वर्गमूल -1 भी होगा।

प्रश्न 2.
(-2)² = 4, क्या 4 का वर्गमूल है -2?
हल:
4 का वर्गमूल -2 भी है।

प्रश्न 3.
(-9)² = 81. क्या 81 का वर्गमूल है – 9?
हल:
81 का वर्गमूल -9 भी है।

(प्रयास कीजिए – पृष्ठ 107)

प्रश्न 1.
से प्रारम्भ होने वाली विषम संख्याओं को बारबार घटाने पर प्राप्त निम्नलिखित संख्याएँ पूर्ण वर्ग हैं या नहीं? यदि यह संख्या पूर्ण वर्ग है तो इसके वर्गमूल ज्ञात कीजिए।
(i) 121
(ii) 55
(iii) 36
(iv) 49
(v) 90
हल:
(i) पूर्ण वर्ग की जाँच करने के लिए 121 में से हम क्रमशः 1 से प्रारम्भ होने वाली विषम संख्याओं को घटाने पर,
121 – 1 = 120
120 – 3 = 117
117 – 5 = 112
112 – 7 = 105
105 – 9 = 96
95 – 11 = 85
85 – 13 = 72
72 – 15 = 57
57 – 17 = 40
40 – 19 = 21
21 – 21 = 0
संख्या 1 से क्रमागत विषम संख्याओं को 121 में से 11 वाँ पद घटाने पर 0 प्राप्त होता है। अत: \(\sqrt{121}\) = 11.

(ii) पूर्ण वर्ग की जाँच करने के लिए 55 में से हम क्रमशः 1 से प्रारम्भ होने वाली विषम संख्याओं को घटाने पर,
55 – 1 = 54
54 – 3 = 51
51 – 5 = 46
46 – 7 = 39
39 – 9 = 30
30 – 11 = 19
19 – 13 = 6,
6 – 15 = -9
∵ 55 को संख्या 1 से क्रमागत विषम संख्याओं से पूर्णत: नहीं हटाया जा सकता है।
∴ 55 एक पूर्ण वर्ग नहीं है।।

(iii) पूर्ण वर्ग की जाँच करने के लिए 36 में से हम क्रमशः 1 से प्रारम्भ होने वाली विषम संख्याओं को घटाएँगे,
36 – 1 = 35
35 – 3 = 32
32 – 5 = 27
27 – 7 = 20
20 – 9 = 11
11 – 11 = 0
अत: 36 पूर्ण वर्ग है और \(\sqrt{36}\) = 6.

(iv) पूर्ण वर्ग की जाँच करने के लिए 49 में से हम क्रमशः 1 से प्रारम्भ होने वाली विषम संख्याओं को घटाएँगे,
49 – 1 = 48
48 – 3 = 45
45 – 5 = 40
40 – 7 = 33
33 – 9 = 24
24 – 11 = 13
13 – 13 = 0
अत: 36 पूर्ण वर्ग है और \(\sqrt{49}\) = 7.

(v) पूर्ण वर्ग की जाँच करने के लिए 90 में से हम क्रमशः 1 से प्रारम्भ होने वाली विषम संख्याओं को घटाएँगे,
90 – 1 = 89
89 – 3 = 86
86 – 5 = 81
81 – 7 = 74
74 – 9 = 65
65 – 11 = 54
54 – 13 = 41
41 – 15 = 26
26 – 17 = 9
9 – 19 = -10
∴ 90 एक पूर्ण वर्ग नहीं है।

(सोचिए, चर्चा कीजिए और लिखिए – पृष्ठ 111)

प्रश्न 1.
क्या हम कह सकते हैं कि एक पूर्ण वर्ग संख्या में यदि n अंक है तो उसके वर्गमूल में \(\frac{n}{2}\), अंक होंगे। यदि n सम है या \(\frac{(n + 1)}{2}\) होंगे यदि n विषम है?
हल:
हाँ, हम कह सकते हैं कि यदि एक पूर्ण वर्ग संख्या में n अंक है, तो इसके वर्गमूल में यदि n अंक है, तो उसके वर्गमूल में
(i) \(\frac{n}{2}\) अंक होंगे, यदि n सम है तथा
(ii) \(\frac{(n + 1)}{2}\) अंक होंगे, यदि n विषम है।
उदाहरण-
(i) सम संख्या \(\sqrt{16}\) = 4, \(\sqrt{2500}\) = 50 आदि
(ii) सम संख्या \(\sqrt{9}\) = 3, \(\sqrt{100}\) = 10 आदि

(प्रयास कीजिए – पृष्ठ 112)

प्रश्न 1.
निम्नलिखित संख्याओं के वर्गमूल में अंकों की संख्या को गणना के बिना ज्ञात कीजिए
(i) 25600
(ii) 100000000
(iii) 36864
हल:
(i) ∵ 25600 में 5 अंक हैं, अतः \(\sqrt{25600}\) में = \(\frac{(n+1)}{2}\) = \(\frac{(5+1)}{2}\) = 3 अंक होंगे।

(ii) ∵ 100000000 में 9 अंक हैं, अतः \(\sqrt{100000000}\) में = \(\frac{(n+1)}{2}\) = \(\frac{(9+1)}{2}\) = 5 अंक होंगे।

(iii) ∵ 36864 में 5 अंक हैं, अतः \(\sqrt{36864}\) में = \(\frac{(5+1)}{2}\) = 3 अंक होंगे।

(प्रयास कीजिए – पृष्ठ 115)

प्रश्न 1.
निम्नलिखित संख्याओं के निकटतम पूर्ण संख्याओं का अनुमान लगाइए
(i) \(\sqrt {80}\)
(ii) \(\sqrt {1000}\)
(iii) \(\sqrt {350}\)
(iv) \(\sqrt {500}\)
हल:
(i) ∵ \(\sqrt {64}\) < \(\sqrt {80}\) < \(\sqrt {81}\)
⇒ 8 < \(\sqrt {80}\) < 9
∵ 81, 64 की अपेक्षा 80 के अधिक नजदीक है।
\(\sqrt {80}\) की निकटतम पूर्ण संख्या 9 है।

(ii) \(\sqrt {1000}\)
∵ \(\sqrt {961}\) < \(\sqrt {1000}\) < \(\sqrt {1024}\)
⇒ 31 < \(\sqrt {1000}\) < 32
∵ 1024, 961 की अपेक्षा 1000 के अधिक नजदीक है।
∴ \(\sqrt {1000}\) की निकटतम पूर्ण संख्या 32 है।

(iii) \(\sqrt {350}\)
∵ \(\sqrt {961}\) < \(\sqrt {350}\) < \(\sqrt {1024}\)
⇒ 18 < \(\sqrt {350}\) < 19
∵ 361, 324 की अपेक्षा 350 के अधिक नजदीक है।
∴ \(\sqrt {350}\) की निकटतम पूर्ण संख्या 19 है।

(iv) \(\sqrt {500}\)
∵ \(\sqrt {484}\) < \(\sqrt {500}\) < \(\sqrt {529}\)
⇒ 22 < \(\sqrt {500}\) < 23
∵ 484, 529 की अपेक्षा 500 के अधिक नजदीक है।
∴ \(\sqrt {500}\) की निकटतम पूर्ण संख्या 22 है।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.5 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.5

निम्नलिखित की रचना कीजिए-

प्रश्न 1.
एक वर्ग READ, जिसमें RE = 5.1 cm.
हल :
हम जानते हैं कि वर्ग की चारों भुजाएँ समान एवं प्रत्येक कोण 90° का होता है ।

(i) सर्वप्रथम हमने RE = 5.1 cm की एक रेखा खींची।
(ii) बिन्दु E पर एक लम्ब | EX बनाया अर्थात् ∠REX =90° बनाया ।
(iii) बिन्दु E को केन्द्र मानकर EA = 5.1 cm की त्रिज्या लेकर एक चाप लगाया, जो EX को A पर काटता है ।
(iv) अब,A को केन्द्र मानकर 5.1 cm का चाप तथा R को केन्द्र मानकर 5.1 cm. का दूसरा चाप लगाया, जो एक दूसरे को D बिन्दु पर काटते है ।
(v) बिन्दु D को R तथा A से मिलाया ।
अतः, READ अभीष्ट वर्ग है।

प्रश्न 2.
एक समचतुर्भुज जिसके विकर्णों की लम्बाई 5.2 cm और 6.4 cm है।
हल :
हम जानते हैं कि एक-दूसरे को समकोण (90°) पर समद्विभाजित करते है।

(i) सर्वप्रथम AC = 6.4 cm. खींची । फिर इस विकर्ण को लम्ब सम-द्विभाजित किया। जो AC को O पर काटता
(ii) O को केन्द्र मानकर \(\frac { 56 }{ 2 }\) = 2.6 cm दूरी लेकर समद्विभाजक के दोनों और चाप बिन्दु B तथा D पर काटे ।
(iii) अब, बिन्दुओं B और D को क्रमशः बिन्दुओं A तथा C से मिलाया ।

इस प्रकार, ABCD अभीष्ट सम-चतुर्भुज हुआ।

प्रश्न 3.
एक आयत जिसकी आसन्न भुजाओं की – लम्बाई 5.0 cm तथा 4.0 cm है।
हल :
हम जानते हैं कि,
आयत के आमने-सामने की भुजाएँ समान एवं इसका प्रत्येक कोण समकोण (90°) होता है?
अत: AB = CD = 5 cm होता है।
BC = DA= 4 cm तथा ∠B = 90°

(i) सर्वप्रथम AB = 5cm रेखा खींची।
(ii) बिन्दु B पर 90° का कोण बनाती हुई BX रेखा खींची।
(iii) बिन्दु B से BC = 4cm का चाप काय ।
(iv) अब, बिन्दु से 5cm तथा बिन्दु A से ।
4 cm के दो चाप काटे, जो एक-दूसरे से बिन्दु D पर मिलते हैं। A 5om

(v) बिन्दु D को क्रमशः बिन्दु A तथा बिन्दु C से मिलाया।
अत: ABCD अभीष्ट आयत है ।

प्रश्न 4.
एक समान्तर चतुर्भुज OKAY, जहाँ OR= 5.5cm तथा KA = 4.2 cm. हैं। क्या यह अद्वितीय है?
हल :
(i) सर्वप्रथम OK = 5.5cm की रेखा खीर्ची ।
(ii) बिन्दु K पर एक किरण KP खींची ।
(iii) किरण KP में से KA = 4.2 सेमी का एक चाप काटा ।
(iv) A को केन्द्र मानकर 5.5cm त्रिज्या का एक चाप लगाया ।
(v) पुनः O को केन्द्र मानकर 4.2 cm का एक चाप लगाया, जो पहले चाप को Y बिन्दु पर काटता है ।
(vi) Y को O तथा A से मिलाया ।

अत: OKAY अभीष्ट समान्तर चतुर्भुज हुआ।

नोट : यह समान्तर चतुर्भुज अद्वितीय नहीं है क्योंकि किरण KP भिन्न-भिन्न कोणों पर खींची जा सकती है। अत: उन भुजाओं से अनेक समान्तर चतुर्भुज बन सकते है ।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.4 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.4

प्रश्न 1.
निम्नलिखित चतुर्भुजों की रचना कीजिए-
(i) चतुर्भुज DEAR, जिसमें
DE = 4 cm
EA = 5 cm
AR= 4.5cm
∠E = 60°
और ∠A = 90° हैं।

(ii) चतुर्भुज TRUE, जिसमें
TR = 3.5 cm
RU = 3 cm
UE = 4 cm
∠R = 75° और
∠U = 120° हैं।
हल :
(i) चतुर्भुज DEAR की रचना निम्नांकित है-

सर्वप्रथम DE = 4 cm की रेखा खींची ।
(ii) ZDEX = 60° बनाया ।
(iii) E को केन्द्र मान कर EA = 5cm काटा ।
(iv) ∠EAY = 90° बनाया ।
(v) A को केन्द्र मानकर और AR = 4.5 cm की त्रिज्या लेकर कोण बनाने वाली रेखा में से एक चाप काटा जो AY को R पर काटता है।
(vi) RD को मिलाया।

अत: DEAR एक अभीष्ट चतुर्भुज है।

(ii) चतुर्भुज TRUE की रचना निम्नांकित है-

(i) सर्वप्रथम TR = 3.5 cm को एक रेखा खींची ।
(ii) फिर ∠TRY = 75° बनाया।
(iii) R को केन्द्र मानकर RU = 3 cm त्रिज्या लेकर एक चाप लगया, जो कोण बनाने वाली रेखा को U पर काटता है।
(iv) अब U पर ∠RUX = 120° का कोण बनाया ।
(v) इस कोण बनाने वाली रेखा UX पर 4cm का चाप लगाया, जो E पर काटता है।
(vi) बिन्दु E को T से मिलाया ।

अत: TRUE अभीष्ट चतुर्भुज हुआ।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.3 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.3

प्रश्न 1.
निम्नलिखित चतुर्भुजों की रचना कीजिए
(i) चतुर्भुज MORE, जिसमें-
MO = 6 cm
OR = 4.5 cm
∠M = 105°
∠R = 105° हैं।

(ii) चतुर्भुज PLAN, जिसमें –
PL = 4 cm
LA = 6.5 cm
∠P = 90°
∠N = 85° है।

(iii) समान्तर चतुर्भुज HEAR, जिसमें-
HE = 5 cm
EA = 6 cm
∠R = 85° है।

(iv) आयत OKAY जिसमें,
OK = 7 cm
KA = 5cm है ।
हल :
(i) चतुर्भुज MORE की Eरचना निम्नांकित है-

(i) सर्वप्रथम MO = 6 cm खींची ।
(ii)0 पर, एक कोण ∠MOX =105° बनाया।
(iii) किरण Ox में से OR = 4.5 cm
(iv) R पर एक कोण ∠ORY = 105° बनाया ।
(v) M पर एक कोण∠OMZ = 60° बनाया तथा किरणें RY और MZ को बिन्दु E पर प्रतिब्छेद कराया।

नोट : प्रतिच्छेद बिन्दु से बढ़ी हई रेखाओं तथा चाप को मिटाना नहीं चाहिए ।
अत: MORE अभीष्ट चतुर्भुज है ।

(ii) चतुर्भुज PLAN की रचना निम्नांकित है-
रचना-
हम जानते हैं कि चतुर्भुज के पारों कोणों का योग 360° होता है।

अत: ∠P + ∠L + ∠A + ∠N = 360°
90° + ∠L + 110° + 85° = 360°
∠L = 360° – 285°
∠L = 75°

(i) सर्वप्रथम PL = 4 cm खींचा ।
(ii) बिन्दु L पर एक कोण ∠PLX = 75° बनाया ।
(iii) किरण LX में से AL = 6.5 cm काटा ।
(iv) A पर एक कोण ∠LAY = 110° बनाया ।
(v) P पर एक कोण ∠LPZ = 90° बनाया । किरणें AY तथा PZ बिन्दु N पर काटती है।

अत: PLAN एक अभीष्ट चतुर्भुज है ।

(iii) समान्तर चतुर्भुज HEAR की रचना निम्नांकित-
रचना-
हम जानते हैं किसमान्तर चतुर्भुज की सम्मुख भुजाएँ “Pass समान तथा सम्मुख कोण समान होते

∠R = ∠E = 85°
∠H = ∠A = 95°

(i) सर्वप्रथम HE = 5cm खींची।
(ii) E पर एक कोण ∠HEX = 85° बनाया।
(iii) किरण EX में से EA = 6cm. काटा ।
(iv) A पर एक कोण ∠EAY = 95° बनाया ।
(v) बिन्दुम पर कोण ∠EHZ = 95° बनाया तथा AY और HZ बिन्दु R पर प्रतिच्छेद होती हैं।

अत: HEAR एक अभीष्ट चतुर्भुज हुआ।

(iv) आयत OKAY की। रचना निम्नांकित है-
रचना-

(i) सर्वप्रथम, हमने OK = 7 cm खींची ।
(ii) बिन्दु K, पर ∠OKA° =90° बनाया ।
(iii) बिन्दु K से लम्ब KA = 5cm काटा, जिसे A नाम दिया ।
(iv) आयत की आमने-सामने की भुजाएँ समान होती हैं।
अत: OK = AY = 7 cm तथा OY = KA = 5 cm.

अब बिन्दु A से 7 cm का तथा बिन्दु०से 5cm का चाप लगाये जो एक-दूसरे को Y पर काटते हैं। Y को A तथा O बिन्दुओं से मिलाया ।
अत: OKAY अभीष्ट आयत है।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 5 आँकड़ो का प्रबंधन Ex 5.1 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 5 आँकड़ो का प्रबंधन Ex 5.1

प्रश्न 1.
निम्नलिखित में से किन आँकड़ों को दर्शाने के लिए आप एक आयत चित्र का प्रयोग करेंगे?
(a) एक डाकिये के थैले में विभिन्न क्षेत्रों के पत्रों की संख्या।
(b) किसी खेलकूद प्रतियोगिता में प्रत्याशियों की ऊँचाइयाँ।
(c) 5 कम्पनियों द्वारा निर्मित कैसेटों की संख्या।
(d) किसी स्टेशन पर प्रातः 7 बजे से सायं 7 बजे तक रेलगाड़ियों से जाने वाले यात्रियों की संख्या। (प्रत्येक के लिए कारण भी दीजिए।)
हल :
(a) विभिन्न क्षेत्रों के पत्रों की संख्या को हम आँकड़ों द्वारा आयत चित्र में नहीं दर्शा सकते हैं।
(b) किसी खेलकुद प्रतियोगिता में प्रत्याशियों की ऊँचाइयों के आँकड़ों को वर्ग-अन्तराल से विभाजित किया जा सकता है । अतः इस आँकड़े को दर्शाने के लिए एक आयत चित्र का प्रयोग कर सकते है।
(c) कैसेटों की संख्या के आँकड़ों को वर्ग-अन्तराल में विभाजित नहीं किया जा सकता है । अतः इसे हम आयत चित्र में नहीं दर्शा सकते हैं।
(d) यात्रियों की संख्या आयत चित्र द्वारा दर्शाई जा सकती है, क्योंकि इन आँकड़ों को वर्ग-अन्तराल में विभाजित किया जा सकता है।

प्रश्न 2.
किसी विभागीय स्टोर पर खरीदारी करने आये व्यक्तियों को इस प्रकार अंकित किया जाता हैपुरुष (M), महिला (W), लड़का (B) या लड़की (G)।
निम्नलिखित सूची उन खरीदारों को दर्शाती है, जो प्रातःकाल पहले घंटे में आये हैं-
W W W G B W W M G G M M W W W W
G B M W B G G M W W M M W W W M
W B W G M W W W W G W M M W W M W G
W M G W M M B G G W.
मिलान चिन्हों का प्रयोग करते हुए एक बारम्बारता बंटन सारणी बनाइए, इसे प्रदर्शित करने के लिए एक दण्ड आलेख खींचिये ।
हल :
बारम्बारता सारणी निम्नांकित प्रकार की होगी-

दण्ड आलेख:
x अक्ष पर खरीदने वाले (M, W, B,G) तथा Y अक्ष पर खरीदने वालों की संख्या दर्शायी गई है ।

प्रश्न 3.
किसी फैक्ट्री के 30 श्रमिकों की साप्ताहिक मजदूरी (रुपयों में) निम्नलिखित हैं-
830,835, 890, 810,835, 836, 869,845, 898, 890,
820,860, 832,833,855,845,804,808, 812, 840,
885,835,835,836,878,840,868,890,806,840.
मिलान चिह्नों (टैली चिह्न) का प्रयोग करते हुए अन्तरालों 800 – 810, 810 – 820 इत्यादि वाली एक बारम्बारता सारिणी बनाइए।
हल :
बारम्बारता सारणी निम्नांकित प्रकार है –

प्रश्न 4.
प्रश्न 3 में दिये आंकड़ों से प्राप्त सारणी के लिए एक आयत चित्र बनाइए और निम्नलिखत प्रश्नों के उत्तर दीजिए-
(i) किस समूह में श्रमिकों की संख्या सबसे अधिक है?
(ii) कितने श्रमिक 850 रुपये या उससे अधिक अर्जित करते हैं?
(iii) कितने श्रमिक 850 रूपये से कम अर्जित करते है ?

हल :
आयत चित्र में X-अक्ष पर मजदूरी तथा Y-अक्ष – पर मजदूरों की संख्या को दर्शाया गया है –

(i) समूह 830-840 में श्रमिकों की सबसे अधिक संख्या है।
(ii) 10 श्रमिक 850 रुपये या उससे अधिक अर्जित करते हैं
∵ 1 + 3 + 1 + 1 + 4 = 10

(iii) 850 रुपये से कम अर्जित करने वाले श्रमिकों की संख्या 20 है।
∵ 5 + 9 + 1 + 2 + 3 = 20

प्रश्न 5.
अवकाश के दिनों में एक विशिष्ट कक्षा के विद्यार्थियों द्वारा प्रतिदिन टेलीविजन (टी. वी.) देखने के समय (घंटों में) दिए हुए आलेख में दर्शाये गये हैं।
निम्नलिखित प्रश्नों के उत्तर दीजिए-
(i) अधिकतम विद्यार्थियों ने कितने घंटों तक टी.वी. देखा ?
(ii) 4 घंटों से कम समय तक कितने विद्यार्थियों ने टी.वी. देखा ?
(iii) कितने विद्यार्थियों ने टी.वी. देखने में 5 घंटे अधिक का समय व्यतीत किया ?

हल :
(i) अधिकतम 32 विद्यार्थियों ने 4-5 घंटे टी. वी. देखा ।
(ii) 4 घंटे से कम समय तक टी. वी. देखने वाले विद्यार्थियों की संख्या 34 है।
∵ (22 + 8 + 4 = 34)
(ii) 14 विद्यार्थियों ने टी. वी. देखने में 5 घंटों से अधिक का समय व्यतीत किया ।
∵ (8 + 6 = 14)

Haryana State Board HBSE 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.2 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.2

प्रश्न 1.
निम्नलिखित चतुर्भुजों की रचना कीजिए-
हल :
(i) चतुर्भुज LIFT, जिसमें-
LI= 4 cm
IF= 3 cm
TL = 2.5 cm
LF = 4.5 cm
IT=4 cm

रचना:
कच्चे चित्र को देखकर हमें सर्वप्रथम ALIT की रचना करेंगे, क्योंकि इस त्रिभुज की तीनों भुजाएँ दी हुई हैं।
(i) सर्वप्रथम LI = 4cm की रेखा खींची । फिर L को केन्द्र मानकर TL = 2.5 cm त्रिज्या से तथा I को केन्द्र मानकर IT = 4 cm त्रिज्या से दो चाप लगाये, जो एक-दूसरे को T बिन्दु पर काटते हैं । T ! को L तथा I से मिलाया ।
(ii) अब L को केन्द्र मानकर CEX LF 24.5cm. तथा I को केन्द्र मानकर IF = 3 cm. त्रिज्याएँ । लेकर क्रमश: दो चाप लगाए, । 4ch जो एक-दूसरे को F पर काटते है ।।

(iii) F को T तथा I से मिलाया। अत: LIFT अभीष्ट चतुर्भुज है ।

(ii) चतुर्भुज GOLD, जिसमें
OL = 7.5 cm
GL = 6 cm
GD = 6 cm
LD = 5 cm
OD = 10 cm है।

रचना-
कच्चे चित्र को देखकर पहले हम GOLD की रचना करेंगे, क्योंकि इस त्रिभुज की तीनों भुजाएँ दी है।
(i) सर्वप्रथम, OL = 7.5 cm की रेखा खीर्ची ।
(ii) L को केन्द्र मानकर 5 cm (LD) की त्रिज्या से तथा O को केन्द्र मानकर 10 cm (OD) की त्रिज्या से क्रमश: दो चाप लगाये, जो एक-दूसरे को D बिन्दु पर काटते है।
(iii) L को D से तथा O को D से मिलाया ।
(iv) L को केन्द्र मानकर 6 cm की त्रिज्या से तथा D को केन्द्र मानकर 6 cm की त्रिज्या से O क्रमशः दो चाप लगाये, जो एक-दूसरे को G बिन्दु पर काटते है।

(v) G को O तथा D से मिलाया । इस प्रकार GOLD अभीष्ट चतुर्भुज हुआ ।

(iii) समलम्ब BEND, जिसमें-
BN = 5.6 cm,
DE = 6.5 cm
रचना-
(i) सर्वप्रथम रेखा DE = 6.5 cm खींची ।
(ii) DE का लम्बसमद्वि-भाजक XY खींचा, जो DE को O पर काटता है ।
(iii) O से ON = \(\frac { 5.6 }{ 2 }\) = 2.8 cm. का चाप लेकर OX पर तथा OB = 2.8 cm. का चाप OY पर लगाया।

(iv) BE, EN, ND और DB को मिलाया ।
अत: BEND अभीष्ट समचतुर्भुज हुआ ।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.1 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 4 प्रायोगिक ज्यामिती Ex 4.1

प्रश्न 1.
निम्नलिखित चतुर्भुजों की रचना कीजिए-
(i) चतुर्भुज ABCD, जिसमें
AB = 4.5 cm
BC = 5.5 cm
CD = 4 cm
AD = 6 cm
AC = 7 cm
हल :
(i) रचना – (i) सर्वप्रथम AC = 7 cm खींचा।
(ii) A को केन्द्र मानकर 4.5 cm (AB) त्रिज्या लेकर एक चाप खींचा।

(iii) C को केन्द्र मानकर 5.5 cm (BC) त्रिज्या लेकर एक चाप खींचा, जो पहले चाप को B पर प्रतिच्छेद करता है।
(iv) A को केन्द्र मानकर 6 cm (AD) त्रिज्या लेकर एक चाप खींचा और C को केन्द्र मानकर 4 cm (CD) त्रिज्या लेकर एक अन्य चाप लगाया। दोनों चाप बिन्दु D पर प्रतिच्छेद करते हैं ।
अब: AB, EC, AD तथा CD को मिलाया ।
ABCD अभीष्ट चतुर्भुज है।

नोट: कोई भी पक्की (Final) रचना करने से पूर्व छात्र प्रश्न में दी गई मापों से कच्चा चित्र बनायें, जिसमें उन्हें पक्की रचना करने में असुविधा नहीं होगी ।

(ii) चतुर्भुज JUMP जिसमें –
JU = 3.5 cm
UM = 4 cm
MP = 5 cm
PJ = 4.5 cm
PU = 6.5 cm
हल :
(ii) चतुर्भुज JUMP की रचना निम्नांकित है-

(i) सर्वप्रथम PU = 6.5 cm खींचा ।
(ii) P को केन्द्र मानकर 5 cm (PM) त्रिज्या लेकर एक चाप लगाया । U को केन्द्र मानकर 4 cm (MU) त्रिज्या से दूसरा चाप लगाया, जो पहले चाप को M पर काटता है।
(iii) P को केन्द्र मानकर 4.5cm (PJ) त्रिज्या से चाप लगाया तथा U को केन्द्र मानकर 3.5cm (JU) त्रिज्या लेकर दूसरा चाप लगाया, जो पहले चाप को J पर काटता है।

(iv) फिर, P को M से, M को U से, P को J से तथा U को J से मिलाया
JUMP अभीष्ट ननुर्भज हुआ।

(iii) समान्तर चतुर्भुज MORE, जिसमें –
OR = 6 cm
EO = 7.5 cm
MO = 7.5 cm
हल :
(iii) समान्तर चतुर्भुज MORE की रचना निम्नांकित है-

समान्तर चतुर्भुज की सम्मुख भुजाएँ समान होती हैं।
अतः MO = 7.5 cm
तथा MO = FR = 7.5 cm
तथा OR = ME = 6 cm
(i) सर्वप्रथम EO = 7.5 cin की रेखा खींची ।
(ii) 0 को केन्द्र मानकर 6 cm (OR) त्रिज्या लेकर एक चाप लगाया तथा E को केन्द्र मानकर 7.5 cm (ER) त्रिज्या लेकर दूसरा चाप लगाया, जो पहले चाप को R पर काटता है।
(iii) 0 को केन्द्र मानकर 7.5 cm (MO) त्रिज्या लेकर एक चाप लगाया तथा E को केन्द्र / मानकर 6cm (EM) त्रिज्या लेकर दूसरा चाप लगाया, जो पहले चाप को M पर काटता है।

(iv)0 को M से, E को M से,०को R से तथा E को R से मिलाया।
अत: MORE अभीष्ट समान्तर चतुर्भुज हुआ है।

(iv) समचतुर्भुज BEST, जिसमें –
BE = 4.5 cm
ET = 6 cm
हल :
(iv) समचतुर्भुज BEST की रचना-
समचतुर्भुज की चारों भुजाएँ समान होती हैं ।
अत: BE = ES = ST = TB = 4.5 cm
(i) सर्वप्रथम TE = 6 cm की रेखा खींची।।

(ii) T तथा E को 4.5 cm क्रमशः केन्द्र मानकर ES = TS = 4.5 cm त्रिज्या B के दो चाप लगाए, जो एक दूसरे को पर काटते हैं ।
(iii) पुनःT तथा E को क्रमशः केन्द्र मानकर 4.5 cm त्रिज्या लेकर दूसरी ओर दो चाप लगाए जो आपस में B पर काटते हैं।

(iv) अब E को S तथा B से और T को S तथा B से मिलाया ।
अतः, BEST अभीष्ट समचतुर्भुज है।

Haryana State Board HBSE 8th Class Science Solutions Chapter 15 Some Natural Phenomena Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 15 Some Natural Phenomena

HBSE 8th Class Science Some Natural Phenomena Textbook Questions and Answers

Question 1.
Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.
Answer:
(b) A copper rod

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
Answer:
(b) becomes positively charged while the cloth has a negative charge.

Question 3.
Write T against true and F against false in the following statements:
(а) Like charges attract each other. (T/F)
(b) A charged glass rod attract a charged plastic straw. (T/F)
(c) Lightning conductor cannot protect a building from lightning. (T/F)
(d) Earthquakes can be predicted in advance. (T/F)
Answer:
(a) False
(b) True
(c) False
(d) False

Question 4.
Sometime, a crackling sound is heard while taking off sweater during winters. Explain.
Answer:
This occurs due to electric discharge between sweater and body. Some energy is always released with electric discharge, which in this case is released in form of a cracking sound.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer:
When we touch a charged body, it loses its charge, due to process of earthing. Our body is good conductor of electricity and transfers the charges to the earth.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer:
Destructive energy of an earthquake is measured in Ricther Scale. Yes, it will be recorded in this scale. Earthquake with megnitude of 3 on Richter Scale is not much destructive.

Question 7.
Suggest three measures to protect ourselves from lightning.
Answer:
Three measure to stay protected from lightning are:

• Stay indore or under covered area.
• Don’t take bath during lightning.
• We should not use T.V. or phone during lighning.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer:
A charged balloon is atracted by another charged balloon because both carry same charge like charge always repel each other. While the uncharged balloon is attracted by charged balloon due to unlike charged.

Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
An electroscope can be used to detect if a body is charged or not. When the metal strips repel each other proves that the body is charged as repulsion is the sure test to detect if a body carries charge or not.

Question 10.
List three states in India where earthquakes are more likely to strike.
Answer:
Kashmir, Punjab and Gujarat are more prone to earthquake.

Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Answer:
We will take following precautions :

• We will try to move to an open space.
• If we are driving, we will slow down the vehicle and move slowly away from that area.
• We will not take shelter under trees or buildings.

Question 12.
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer:
No, we will not take an umbrella, as this will increase the risk of lighting because wide objects are more prone to lightning strike.

Extended Learning – Activities and Projects

Question 1.
Open a water tap. Adjust the flow so that it forms a thin stream. Charge a refill. Bring it near the water stream. Observe what happens. Write a short report on the activity.
Answer:
For self attempt.

Question 2.
Make your own charge detector. Take a paper strip roughly 10 cm x 3 cm. Give it a shape as shown in Fig. 15.15. Balance it On a needle. Bring a charged body near it. Observe what happens. Write a brief report, explaining its working.
Answer:
For self attempt.

Question 3.
This activity should be performed at night. Go to a room where there is a fluorescent tube light. Charge a balloon. Switch off the tube light so that the room is completely dark. Bring the charged balloon near the tubelight. You should see a faint glow. Move the balloon along the length of the tube and observe how glow changes.
Caution: Do not touch the metal parts of the tube or the wires connecting the tube with the mains.
Answer:
For self Attempt.

Question 4.
Find out if there is an organisation in your area which provides relief to those suffering from natural disaster. Enquire about the type of help they render to the victims of earthquakes. Prepare a brief report on the problems of the earthquake victims.
For more information on these topics, visit:
→ science.howstuffworks.com/lightning.htm
→ science.howstuffworks.com/ earthquake .htm
→ www enchantedlearning.com/subjects/ astronomy/planets/ earth/continents.shtml
Answer:
For self attempt.

HBSE 7th Class Science Some Natural Phenomena Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name any three natural phenomena.
Answer:
Earthquakes, cyclones, lightning.

Question 2.
According to ancient Greeks who invented thunderbolts?
Answer:
Goddess of Wisdom Minerva.

Question 3.
What are the sparks seen in sky during thunderstorms?
Answer:
Lightning.

Question 4.
Which resin did Greeks knew, produced sparks on rubbing continuously?
Answer:
Amber.

Question 5.
What happens when we rub a plastic scale with our hair?
Answer:
It gets charged.

Question 6.
What happens when charged plastic scale is brought close to bits of paper?
Answer:
Papers get attracted towared scale.

Question 7.
What happens when we rub an inflated balloon and let it free near a wall?
Answer:
Balloon gets attached to the wall.

Question 8.
How many types of charges are gained by rubbing objects?
Answer:
Two.

Question 9.
Name the charges bodies acquire on rubbing.
Answer:
Positive charge and negative charge.

Question 10.
What happens when similar charged bodies are brought close?
Answer:
They repel each other.

Question 11.
What happens when two different charged bodies are brought close?
Answer:
They attract each other.

Question 12.
What will happen when a charged glass rod is brought close to a charged straw?
Answer:
They will attract each other.

Question 13.
What will happen when a charged pen refil is brought close to a charged balloon?
Answer:
They attract each other.

Question 14.
Which charge is conventionally called a positive charge?
Answer:
Charge on a charged glass rod.

Question 15.
A charged glass rod attracts a charged straw. What is the charge on the charged straw?
Answer:
Negative charge.

Question 16.
What is the electric charge generated by rubbing called?
Answer:
Static electricity.

Question 17.
What is the static electricity?
Answer:
Charges which are produced by rubbing and are not movable are called static electricity.

Question 18.
How is electric charges different from static charges?
Answer:
Electric charges can flow but static charges cannot move.

Question 19.
What is used to transfer electrical charges from one body to another?
Answer:
Metallic conductors.

Question 20.
What is the transfer of charges from one body to earth is called?
Answer:
Earthing.

Question 21.
What provision is made in buildings to prevent electrocution?
Answer:
Earthing of wires is done.

Question 22.
How a huge energy is produced during thunderstorm?
Answer:
By repulsion of negative charges from clouds and positive charges from ground.

Question 23.
What is the process of meeting of negative charges from clouds with positive charges from ground to release huge energy called?
Answer:
Electric discharge.

Question 24.
Which place is safe during thunderstorms and lightning?
Answer:
Covered vehicles and buildings.

Question 25.
What should be considered as alert signs to get a safe place during thunderstroms?
Answer:
Hearing thunder without lightning.

Question 26.
Is sitting on a motor-cycle safe during lightning?
Answer:
No.

Question 27.
Where should one take shelter in open during lightning?
Answer:
Under small trees.

Question 28.
Is it safe to use wired phones during lightning?
Answer:
No.

Question 29.
Can a lightning victim electrocute another person?
Answer:
No.

Question 30.
What harms can lightning cause in a lightning victim?
Answer:
Loss of memory, loss of hearing or sight, broken bones etc.

Question 31.
What is the device used to save multistoryed buildings from lightning.
Answer:
Lightning rod.

Question 32.
Where is the lightning rod attached to protect the building from lightning?
Answer:
On the top of the building.

Question 33.
One end of the lightning rod is left loose in the air, where is the other end fixed or attached?
Answer:
Other end of the rod is attached to the ground.

Question 34.
Which fish can give electrical shock?
Answer:
Electrical eel.

Question 35.
What is the capacity of producing electric current in an electrical eel?
Answer:
650 volts.

Short Answer Type Questions

Question 1.
How can charging take place by rubbing?
Answer:
When a plastic comb is rubbed with hair it starts attracting small pieces of paper. Similarly, when two straws are rubbed with polythene and are brought close they repel each Other. Rubbing charges the comb and straws by loading charges on comb and straws, The polythene and hair against which straws and combs are charged also get charged.

Question 2.
How many types of charges do things acquire on rubbing?
Answer:
Charges acquired by objects are of two types named positive charge and negative charge. Charge acquired by a glass rubbed with silk is called positive charge and the charge acquired by the silk is called the negative charge.

Question 3.
How are negative and positive charges related to each other?
Answer:
Positive charges repel each other and negative charges repel each other. In other words similar charges repel each other. On the other hand negative charge is attracted by positive charges or in simple words opposite charges attract each other.

Question 4.
What is static electricity? How is it different from electric current?
Answer:
The electrical charges acquired by bodies on rubbing are called static electricity. These charges are called static because, they cannot move. This is the difference static electricity and electrical current has. Electrical current can move or flow but static electricity cannot move or flow.

Question 5.
What is electrical discharge?
Answer:
Transfer of charges from a body is called electrical discharge. If we touch a charged object, the charge gets transferred to the earth through our body. We say that the object is discharged. This is also called earthing. Electrical discharge can take place between any two conducting bodies.

Question 6.
How electrical discharge takes place in clouds?
Answer:
During thunderstorms the negative charges get accumulated near the clouds and positive charges accumulate near ground. When these negative and positive charges meet, electrical discharge takes place between clouds and grounds. It produces huge amount of energy which is released as lightning and thunder.

Question 7.
How do clouds get charged during thunderstorms?
Answer:
During thunderstorm there is a vigorous movement of air current in upward and downward direction i.e. in opposite direction. This is similar to rubbing of objects, this vigorous movements of water droplets in clouds cause charging of the clouds.

Question 8.
How does lightning strike during thunderstroms?
Answer:
During thunderstorms, the opposite charged clouds and ground come in contact and electrical discharged takes place between clouds and ground and huge energy is released as lightning. This is called lightning strike. Electrical discharge can take place between clouds and ground, clouds and human body, clouds and building etc.

Question 9.
How can we protect ourselves from lightning during thunderstorm when we are out of our home?
Answer:
Following precautions should be used when we are out during thunderstorm:

• We should not stay in open vehicles or places.
• Should not carry unbrella.
• Should not take shelter under tall trees or under poles etc.
• If shelter has to be taken, then it should be taken under smaller trees.

Question 10.
What precautions should we take to secure ourselves from lightning stroke during thunderstorm when we are in our homes?
Answer:
Following precautions should be taken while in house :

• We should not use wired phone.
• Electrical appliances should be plugged off.
• Should not bathe in running water.

Question 11.
Why is it advised to take shelter under smaller trees while in open during thunderstorms?
Answer:
During thunderstorms, we should take shelter under smaller trees because electrical discharge can easily take place with tall trees, so they are easy targets of lightning. While smaller trees are not in reach of lightning often.

Question 12.
How does a lightning rod protect a building from lightning?
Answer:
Lightning rods are installed on the top of the buildings. One end of the rod is left in open and the other one is connected to the earth.When lightning strikes the building, the charges are directly transferred to earth by the rod, this is called earthing. Earthing thus saves the buildings from lightning strike.

Question 13.
Why the Electric Eel is so called?
Answer:
Eel found in South America emits electric discharge from its body. It can produce electric current of 650 volts. It emits discharge to attack its enemies, to give shock to the prey. It can also give shock to human beings too. As these Eels produce electric discharge, they are called electric Eels.

Question 14.
What is an earthquake? How is it measured?
Answer:
Sudden trembling and shaking of the earth is called an earthquake. Due to sudden movements in the uppermost layer of the earth, the earth starts trembling, this movement of earth is called an earthquake. The magnitude of the earthquake is measured through an instrument called seismograph and it is measured on Richter scale.

Long Answer Type Questions

Question 1.
What is static electricity? How many kinds of charges are there?
Answer:
The electrical charge produced due to rubbing of objects is called static electricity. This charge cannot move as the electric current moves. These types of charges are produced only when objects are rubbed. When we rub an inflated balloon with our hair and let it loose, it attaches to wall. This proves that balloon has been charged. Similarly when a glass rod is rubbed with silk, it gets charged.

Charges are of two types : Negative charges and positive charges. Conventionally charge acquired by a glass rod is called positive charges and the charges acquired by the silk with which glass rod is rubbed aquires a negative charge. Similarly charged bodies repel each other and oppositely charged bodies attract each ether.

Question 2.
What is earthing? How is it useful?
Answer:
Transfer of charges to earth through conducting bodies is called earthing. In buildings wiring is done to do earthing when we touch the electric current, it enters the earth through our bodies. The bodies of the living beings including humans are good conductors of electricity. So, they easily acquire charges and transfer them to the earth, if they are in contact of the earth. This is called earthing.

Earthing is very useful as it protects us from electrocution. It prevents electric shocks as it transfers current to the earth. Earthing also saves building from lightning.

Question 3.
How does lightning take place during a thunderstorm?
Answer:
Lightning during thunderstorm takes place due to a phenomenon known as electric discharge. Electric discharge means interaction between oppositely charged objects. During thunderstorms vigorous upward and downward movement of air particles take place. This causes charging of water droplets accumulate in clouds and positive charge accumulates near ground. When these positive charges and negative charges meet a huge amount of energy is released in form of thunder and lightning. This whole process is called electrical discharge.

Question 4.
How can we save ourselves from lightning?
Or
What precautionary measures should be taken to save ourselves from lightning?
Answer:
Lightning gives a warning before appearing. Huge thunder without light is a warning. We should look for a safe place. No place in open is safe.

• One should rush to take shelter in building or house.
• One should not come out of the covered vehicle if on the road.
• One should not keep sitting on open vehicles like scooters, bikes etc.
• One should not take shelter under large and tall trees as they are easy target for electrical discharge.
• One should take shelter under smaller trees while in open as they are not easy target of lightning.
• If in open and no tree or shelter nearabout, one should sit with head folded under arms and embedded between the legs. One should not lie down in open.
• We should plug out all the electrical appliances during lightning.
• We should not use wired telephones during lightning, while mobiles and cordless phones are safe.
• One should not take ones bath during lightning.

Question 5.
What is a lightning rod? How is it used?
Answer:
Lightning rod is a device which is used to save tall buildings from lightning. Tall buildings are easy target to lightning as there can be easy electrical discharge with clouds. Lightning rod is a rod having three spikes on its top and a long earthing- wire to be attached to the earth. The end with spikes is left in open and other end is attached to earth. Lightning rod is fitted on the top of the buildings. During thunderstorm, when electrical discharge takes place between clouds and the building, the lightning rod acquires the charges and transfers them to the earth through its embedded end and saves the buildings from the strike of the lightning.

Question 6.
What is an earthquake? How does it occur?
Answer:
Sudden shaking and trembling of the earth is called earthquake. It occurs due to disturbance deep inside the upper layer of the earth. Earthquake is a natural phenomenon, which can be very devastating depending upon its intensity and magnitude.

The uppermost layer of the earth is not made up of a single flat surface. It is made up of different fragments, called seismic plates. These plates are joined with each other at different points. These plates are always in a continuous motion. Sometimes due to collision of these plates or upward or downward motion of these plates earth starts shaking. This is called an earthquake. The areas falling between these plates are the areas which are the most vulnerable areas for earthquakes. These are called fault zones or in simple language danger zones.

Question 7.
What is a seismograph? How does it work?
Answer:
Seismograph is an instrument which is used to record the intensity of the earthquake. Seismograph has a long rod suspended, with a pen attached to it. A paper is placed under the pen. When an earthquake strikes, the rod starts vibrating. The pen also starts vibrating and paper starts moving under the pen recording the movement of the pen. Scientists further study the seismic waves recorded by pen and make estimates about the intensity of the earthquake. This graph also gives the idea about the energy involved in the earthquake. This idea helps in determining the destructive power of the earthquake.

Some Natural Phenomena Class 8 HBSE Notes

• Natural phenomena like lightning, earthquakes etc. always made people fearful. People had many superstitions regarding these phenomena. They related these phenomenon to wrath and pleasures of Gods.
• Greeks knew that sparks like that of lightning also Occur when amber is rubbed with fur.
• Rubbing the objects with other objects can cause charging like rubbing a plastic scale with hair can charge the scale.
• Similar charged bodies repel each other while oppositely Charged bodies attract each other.
• Charges are of two types : negative and positive.
• Charges on a charged glass rod is said to be positive and other kind of charges are called negative charges.
• Opposite charges attract each other and similar charges repel each other.
• Charges which are generated due to rubbing are called static electricity. Static electricity means where charges do not move as in electric current.
• Charges can be transferred from one body to another. Charges can be transferred from a charged body to earth and this is called earthing.
• Lightning during rain is due to release of huge energy during electric discharge.
• Lightning can be dangerous, but we can secure ourselves by using precautions.
• Lightning rods can protect tall building from lightning as tall objects are easy target for lightning.
• Earthquake is another natural phenomena which can prove disastrous.
• Earthquakes take place due to disturbance in upper crusts of the earth.

Haryana State Board HBSE 8th Class Science Solutions Chapter 17 Stars and the Solar System Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 17 Stars and the Solar System

HBSE 8th Class Science Stars and the Solar System Textbook Questions and Answers

Question 1.
Which of the following is NOT a member of the solar system?
(a) An asteroid
(b) A satellite
(c) A constellation
(d) A comet
Answer:
(c) A constellation

Question 2.
Which of the following is NOT a planet of the sun?
(a) Sirius
(b) Mercury
(c) Saturn
(d) Earth
Answer:
(a) Sirius

Question 3.
Phases of the moon occur because:
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of the moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.
Answer:
(c) the shadow of the Earth covers only a part of the moon’s surface.

Question 4.
Fill in the blanks :
(a) The planet which is farthest from the Sun is __________.
(b) The planet which appears reddish in colour is __________.
(c) A group of stars that appear to form a pattern in the sky is known as a __________.
(d) A celestial body that revolves around a planet is known as __________.
(e) Shooting stars are actually not __________.
(f) Asteroids are found between the orbits of __________ and __________.
Answer:
(a) Neptune
(b) Mars
(c) constellation
(d) Satellite
(e) Meteors
(f) Mars and Jupiter.

Question 5.
Mark the following statements as true (T) or false (F) :
(а) Pole star is a member of the solar system. ( )
(b) Mercury is the smallest planet of the solar system ( )
(c) Uranus is the farthest planet in our solar system. ( )
(d) INSAT is an artificial satellite. ( )
(e) There are nine planets in our solar system. ( )
(f) Constellation Orion can be seen only with the telescope. ( )
Answer:
(a) False
(b) False
(c) False
(d) True
(c) False
(f) False

Question 6.
Match items in Column A with one or more items of Column B :

A	B
(i) Inner planets	(a) Saturn
(ii) Outer planets	(b) Pole star
(iii) Constellation	(c) Great Bear
(iv) Satellite of the Earth	(d) Moon
	(e) Earth
	(f) Orion
	(g) Mars

Answer:

A	B
(i) Inner planets	(g) Mars, (e) Earth
(ii) Outer planets	(a) Saturn
(iii) Constellation	(c) Great Bear, (f) Orion
(iv) Satellite of the Earth	(d) Moon

Question 7.
In which part of the sky can you find Venus if it is visible as an evening star?
Answer:
In western sky.

Question 8.
Name the largest planet of the solar system.
Answer:
Jupiter.

Question 9.
What is a constellation? Name any two constellations.
Answer:
A group of stars in a recognizible shape is called a constillation. Orion and the Great Bear are constellations.

Question 10.
Draw sketches to show the relative positions of prominent stars in (i) Ursa Major and (ii) Orion.
Answer:

Question 11.
Name two objects other than planets which are members of the solar system.
Answer:
Meteors and Asteroids.

Question 12.
Explain how you can locate the Pole Star with the help of Ursa Major.
Answer:
Pole star is situated at the end of the Ursa Major. If a straight line starting from the last two stars is extended towards the north direction, it will lead to the Pole Star.

Question 13.
Do all the stars in the sky move? Explain.
Answer:
All the stars in the sky do not move, but they appear to move from east to west. This is actually due to rotation of earth on its axis. Earth moves from west to east. So it appears as the stars are rising from east and as the day dawns they sets in the west.

Question 14.
Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the earth?
Answer:
Stars are away from the earth millions of kilometres away. It is not convenient to express such a large distance in the units of km. So the distance of stars from the earth is expressed in time taken by light to travel in one year. Eight light years mean time taken by light to travel in eight years.

Question 15.
Boojho made the following sketch (figure) of the solar system. Is the sketch correct? If not, correct it.
Answer:
No, the sketch is incorrect. The following sketch is correct.

Extended Learning – Activities and Projects

Question 1.
If possible, visit a planetarium. There are planetariums in many cities. In a planetarium you can see the motion of the stars, constellations and planets on a large dome.
Answer:
For self attempt.

Question 2.
On a moonless night observe the sky for a few hours. Look out for a meteor, which appears as a streak of light. September-November is a good time for observing meteors.
Answer:
For self attempt.

Question 3.
Learn to identify the planets visible to the naked eye and some prominent constellations such as Great Bear (Saptarshi) and Orion. Also try to locate the Pole Star and the star Sirius.
Answer:
For self attempt.

Question 4.
Select a convenient place on the roof of your house or in some playground from where you can watch sunrise clearly. Remember that you will have to do this activity for a few months. So, choose the place carefully. On a sheet of chart paper draw the outline of the eastern horizon indicating big trees, poles, etc. Mark the outline of the sheet so that you can place it in the same position every time. After every two weeks, note the position from where the Sun rises and mark this on your chart paper (Fig.). Also note the date of your observation. Repeat this for a few months. It is advisable that you start observations in the month of November or May.

Does the Sun always rise from the same direction? Discuss your observations with you teacher, parents and elderly people in your family or in the neighbourhood.
Answer:
For self attempt.

Question 5.
Form a group of studens. Prepare a model of the solar system showing the planets, and their relative sizes. For this take a large chart paper. Make spheres representing different planets according in their relative size (Use Table). You may use newspaper, clay or plasticine to make spheres. You can cover these spheres with paper of different colours. Exhibit your model in the class.

Name of Planet	Approximate radius (assuming Earth as 1 unit)	Approximate distance from the Sun (Assuming distance of the Earth as 1 unit)	Period of revolution	Period of rotation
Mercury	0.40	0.39	88 days	59 days
Venus	0.95	0.72	225 days	243 days
Earth	1.00	1.00	365.25 days	24 hours
Mars	0.55	1.50	687 days 24 hours	37 min
Jupiter	11.00	5.20	12 years 9 hours	55 min
Saturn	9.00	9.50	29.46 years	10.66 hours
Uranus	4.00	19.20	84 years	17.2 hours
Neptune	3.90	30.00	165 years	16.1 hours

Answer:
For self attempt.

Question 6.
Try to make a scale model of the solar system showing distances of the planets from the Sun (Use Table 17.1). Did you face any difficulty? Explain it.
Answer:
For self attempt.

Question 7.
Solve the following riddle and try to make similar riddles yourself:
My first is in VAN but not in PAN
My second is in EARTH and also in HEAVEN
My third is in ONE and not in TWO
My fourth is in BUN and also in FUN
My last is in STAR but not in RADAR
I am a planet that moves round the Sun.
You can read more on the following websites:
→ http://www.nineplanets.org
→ http://www.kidsastronomy.com
→ http://www.solarsystem.nasa.gov/planets
→ http://aa.usno.navy.mil/fazz/does/moon- phases.html
Answer:
For self attempt.

HBSE 7th Class Science Stars and the Solar System Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name any three celestial bodies.
Answer:
Stars, Satellite, Planets.

Question 2.
Name the planets of solar system which cannot be seen by naked eye?
Answer:
Neptune and Pluto.

Question 3.
Name the force which makes planets move around the sun.
Answer:
Gravitational force.

Question 4.
Which has higher density : Earth or Sun?
Answer:
Earth.

Question 5.
Name the planet narest to earth.
Answer:
Mars is nearest to earth.

Question 6.
Write the names of any two constellation.
Answer:
Great Bear and Orion.

Question 7.
A group of stars visible in winter season look like a cluster of twinkling gems.
Answer:
Pleiades constellation.

Question 8.
In which season of the year are the constellations scorpio and orion visible in the Northern Hemisphere?
Answer:
Orion – Winters.
Scorpio – Summers.

Question 9.
Define star.
Answer:
Stars are the heavenly bodies that are extremely hot and have light of their own.

Question 10.
Name the star which is nearest to the earth.
Answer:
Alpha Centuari.

Question 11.
Write the names of two planets which are closer to the sun than the earth.
Answer:
Mercury and Venus.

Question 12.
Name the planet nearst to the sun.
Answer:
Mercury.

Question 13.
Name the planet farthest from the sun.
Answer:
Neptune.

Question 14.
Which planet of the solar system is the hotest?
Answer:
Mercury.

Question 15.
Name the planet of the solar system Which is nearer to the Sun and Venus.
Answer:
Mercury.

Question 16.
Which planet in the solar system is nearest to the earth?
Answer:
Venus.

Question 17.
Name the planet, where there is no carbon dioxide.
Answer:
Mercury.

Question 18.
Name the planets, which has no moon?
Answer:
Mercury and Venus.

Question 19.
Give any two applications of remote sensing.
Answer:
(i) Preparing waste land maps.
(ii) Survey for ground water and mineral resources.

Question 20.
A constellation having seven prominent stars, is visible during the winter. Name the constellation.
Answer:
Orion.

Question 21.
A belt of assorted debris, which failed to assemble into a planet, is located between the orbits of two planets in the solar system. Name these two planets.
Answer:
Mars and Jupiter.

Question 22.
Which planet has rings around it?
Answer:
Saturn.

Question 23.
Name largest asteroid.
Answer:
Ceres.

Question 24.
Why do meteors shine?
Answer:
On entering earth’s atmosphere, meteors become hot and bum due to friction of earths atmosphere and start to shine.

Question 25.
What are meteorites?
Answer:
Big pieces of rock material which do not bum completely in atmosphere of earth, fall on its surface. These are called meteorites.

Question 26.
How are comets formed?
Answer:
When the path of objects near the edge of solar system is disturbed to push them near to sun, comets are formed.

Question 27.
After how much time Halley’s comet is seen?
Answer:
After every 76 years.

Question 28.
Why does pole star appear to be stationary?
Answer:
Pole star lies on the axis of rotation of earth and appears stationary when viewed from any part of earth.

Question 29.
What does the colour of a star signify?
Answer:
Colour of a star signifies its temperature.

Question 30.
Define a satellite.
Answer:
A satellite is a solid heavenly small sized body revolving round a planet.

Short Answer Type Questions

Question 1.
Distinguish between stars and planets.
Answer:

Star	Planet
(i) Star has its own light.	(i) Planet does not have its own light.
(ii) Star seems to move from east to west in the sky.	(ii) Planet moves around a star called sun.
(iii) Stars are very big and gaseous in nature.	(iii) Plants are comparatively small but appear big because they are nearer to earth.

Question 2.
Explain the importance of stars for the people in ancient times.
Answer:
In ancient times when there were no compass, night sky was very useful in finding the direction. As pole star remains fix in the sky in north, it indicated north direction. As the stars change their position with time, it has been possible to find the time with relative position of stars.

Question 3.
How is the pole star located in the sky? Why is it so special?
Answer:
The earth rotates on its axis from west to east, therefore, the stars appear to move in opposite direction, i.e. east to west. But pole star lies on the axis of rotation of earth which is fixed, Therefore, pole star also seems to be fixed in the sky. It is always in north direction and is very useful for finding direction.

Question 4.
Distinguish between star and shooting star.
Answer:

Star	Shooting star
(i) It has its own light.	(i) It produces light when it becomes hot after entering in earth’s atmosphere.
(ii) Star is a gaseous body.	(ii) It is not a star at all and is made of rocky material.
(iii) Has a very long life.	(iii) Lasts only for a very short time.

Question 5.
What is a meteor? Why does it last for a very short time?
Answer:
Meteors are the heavenly bodies made of rocky material which enter earth’s atmosphere. When they travel through air they become hot and burn because of friction. Due to this, these rocky pieces melt and vaporises very fast and do not last long.

Question 6.
Distinguish between natural and artificial satellites.
Answer:
Natural satellites are far away from planets. They are comparatively larger in size and are present naturally. Artificial satellites are sent from earth with specific requirements. Their distanc, size and mass are lesser than the natural satellite.

Question 7.
What is solar system? Name the planets situated between the sun and the earth?
Answer:
The solar system consists of the sun, eight planets; and their satellites and other heavenly bodies like meteors, comets and asteroids. The sun is the centre of the solar system and all the planets revolve around the sun in elliptical paths called orbits. The planets situated between the sun and the earth are Mercury and Venus.

Question 8.
What are the phases of the Moon?
Answer:
Moon has no light of its own. It reflects light of the Sun falling on it. On new moon day, moon is between the sun and the earth and no reflected light from it reaches the earth. We cannot see moon on that day. The visible moon increases every day till fifteenth day from the new moon day, the full phase of the moon is visible.

Positions of the Moon in its orbit and its corresponding phases
So, the waxing and waning of moon periodically as it revolves around the earth is called phases of moon.

Question 9.
Why moon cannot be used as a communication satellite?
Answer:
Moon is a natural satellite of the earth but it cannot be used as a communication satellite because :

• It is very far away from earth.
• Its time period 27.3 days is too large.
• It has neither equitorial orbit nor polar orbit which makes a satellite useful for different purposes.

Question 10.
What are constellations? Name some easily recognizible constellations in the sky.
Answer:
Group of stars forming a recognizible shape is called a constellation. These group of stars are identified in different shapes. Constellations do not change their shape. They also appear to move from east to west as other stars appear to. Some major constellations are Ursa Major, Ursa Minor, Orion, Cassiopeia etc. Some of them are visible during summers while some are visible during winters.

Question 11.
What are various types of motions associated with the planet earth?
Answer:
The earth has four types of motion. These are :

(i) The earth’s daily rotation on its axis.
(ii) The earth’s annual revolution around the sun.
(iii) The earth’s precession (conical motion of earth’s axis).
(iv) As a part of solar system, the earth’s motion in space along with the sun.

Question 12.
Explain the constellation Ursa Major.
Answer:
Ursa Major is one of the most famous constellation. We can see this constellation during summers. It is also called the Great Bear or the Saptarishi. There are seven prominently shining stars in this constellation which are arranged in shape of a question mark. At the tail of this constellation lies the Pole Star.

Question 13.
Describe the constellation also called the hunt.
Answer:
A well known constellation named Orion is also called the hunter. This constellation can be seen in the late evenings of winter. It has seven or eight brightly shining stars arranged in shape recognized with hunter. The brightest star in the sky Sirius is located at the extended line from the tail of this constellation.

Question 14.
What are asteroids?
Answer:
Asteroids are the small objects which revolve around the sun in a large gap between the orbits of Mars and Jupiter. These are quite large in their number and are considered as the part of our solar system. Each asteroid has its own orbit.

Question 15.
What are comets?
Answer:
Comets are the part of our solar system which revolve around the sun in highly elliptical orbits. It appears with a bright head and a long tail. The length of the tail grows in size as it approaches the sun. The tail is always directed away from sun.

Question 16.
What are various superstitions connected with appearance of comets?
Answer:
They are considered to be the messangers of destruction and disasters. They are supposed to bring wars,epidemics and flood with them. So, their appearance is considered as unauspicious.

Question 17.
List five uses of artificial satellites.
Answer:

• Weather forecasting.
• Radio and television transmission.
• Long distance communication.
• Locating mineral resources.
• Gathering information about our space.

Long Answer Type Questions

Question 1.
Explain celestial sphere.
Answer:
The large imaginary sphere on which all the heavenly bodies like stars, planets and satellites seems to lie is known as celestial sphere. Since we are on the earth, the earth appears stationary to us. When we look at the sky, the various objects in the sky like the stars and the moon appear to be moving round the earth. In other words, the celestial sphere appears to be moving from east to west round the earth. This apparent motion of the celestial sphere from east to west is actually due to the daily rotation of the earth from west to east. Since the earth rotates from west to east, the celestial sphere appears to rotate in the opposite direction, from east to west.

Question 2.
What are constellations? Explain. Name some prominent constellations with their Indian names.
Answer:
The groups of stars which seem to be arranged in the sky in beautiful patterns and recogniseable shapes are known as constellations. With each constellation, the ancient astronomers assigned the name of an object which it appears to resemble. There are 88 constellations into which the whole of the sky has been divided. In Indian astronomy, the constellations are known as Nakshatras.

Some prominent constellations with their Indian names are given below :
(i) Ursa Major or Saptarishi.
(ii) Ursa Minor or Laghu Saptarishi
(iii) Orion or Mriga or Vyadha
(iv) Tarus or Vrashba
(v) Scorpio or Vrishchika.

Question 3.
What is pole star? What is specific j about its position in the sky?
Answer:
There is only one star in the sky which appears stationary to an observer on earth. This star is named as pole star (Polaris) or Dhruvtara in India. This star appears stationary because, i it lies in the direction of the axis of the Earth about which the earth rotates. Any point on or j along the axis of a rotating body appears to be stationary. So, the pole star that lies along the direction of the axis of rotation of the earth, always sppears to be stationary.

Question 4.
What are artificial satellites? Explain their usage.
Answer:
Man made objects orbitting in outer space around the earth or any other planet are called artificial satellites of earth or that particular planet. The satellite like INSAT 3E or Kalpana Chawla I are examples of artificial satellites. Artificial satellites have many practical applications that effect our lives in many ways, i Long distance transmission of television programmes, communication through telephones and internet could be possible because of them. Artificial satellites are also used for research, defence and remote sensing. Remote sensing means collecting information from a distance. Information is collected regarding weather, agriculture, land and ocean features including movement of fish.

 Stars and the Solar System Class 8 HBSE Notes

• We can see many celestial bodies in a clear night sky.
• Stars are one of the celestial bodies which emit light of their own.
• Sun is also one of the stars which emits light and is a great source of heat. It is the closest star which is the centre of our solar system.
• Stars are many light years away from the earth and thus look very small from earth.
• Stars appear to travel from east to west.
• Pole star is the most shining star in the night sky. The pole star appears to.be stationary. It is situated near axis of rotation of earth and is thus helpful in finding direction.
• A group of stars, appearing in different shapes are called constellations. Their shapes resemble different objects and thus are named after the names of the objects.
• Other improtant parts of night sky are the planets. Planets are those celestial bodies, which revolve around sun.
• Our solar system consists of eight planets revolving around sun. It also consists of many other celestial bodies like asteroids, comets and meteors.
• Comets are the celestial bodies that revolve in highly elliptical orbits around sun.
• Bright streak of light in a night sky are commonly called shooting stars or meteors.
• A celestial body revolving around another celestial body is called a satellite.
• Artificially sent bodies in space, which revolve around earth or any other planet or a natural satellite is called an artificial satellite
• Jupiter is the largest planet while Venus is brightest planet in the night sky.
• Moon is the natural satellite of the earth. Moon appears in different phases. The phases of Moon occur because we can see only that part of the moon which reflects light towards us.

Haryana State Board HBSE 8th Class Science Solutions Chapter 10 Reaching the Age of Adolescence Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 10 Reaching the Age of Adolescence

HBSE 8th Class Science Reaching the Age of Adolescence Textbook Questions and Answers

Question 1.
What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer:
Hormones.

Question 2.
Define adolescence.
Answer:
Adolescence: The period of life, when the body undergoes changes, leading to reproductive maturity is called adolescence.

Question 3.
What is menstruation? Explain.
Answer:
When egg produced by ovary does not get fertilized, it along with the thickened lining of the uterus and blood vessels get flown off out of the body every month as bleeding in women. This is called menstruation.

Question 4.
List the changes in the body that take place at puberty.
Answer:
Certain changes take place in the bodies of boys and girls at age of puberty. These include:
(i) Growing of hair at different body parts
(ii) Sudden increase in height.
(iii) Growth of moustaches and beards in boys.
(iv) Voice,of boys get coarsed.
(v) Development of breast in girls and hips get heavy.
(vi) Development of sex organs.

Question 5.
Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer:

Endocrine Organs	Hormones secreted
(i) Thyroid	(i) Thyroxine
(ii) Pancreas	(ii) Insulin
(iii) Adrenal glands	(iii) Adrenalin
(iv) Pituitary gland	(iv) Growth hormones
(v) Testes	(v) Testosterone
(vi) ovaries	(vi) Estrogen

Question 6.
What are sex hormones? Why are they named so? State their function.
Answer:
Hormones which constitute the secondary sexual characters are called sex hormones. They are called sex hormones because it is because of them that sex is diferentiated i.e. a boy is distinguished from a girl due to these hormones. Their function is to develop the secondary sexual characters in boys and girls.

Question 7.
Choose the correct option:
(a) Adolescents should be careful about what they eat, because ………….
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
Answer:
(ii) proper diet is needed for the rapid growth taking place in their body.

(b) Reproductive age in women starts when their …………..
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
Answer:
(i) menstruation starts.

(c) The right meal for adolescents consists of …………
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
Answer:
(ii) chapati, dal, vegetables.

Question 8.
Write notes on:
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
Answer:
(a) Adam’s Apple:
Adam’s apple is a protruding part in the throat. It is the enlarged voice box or larynx, which gets enlarged at the onset of puberty. This makes the voice of the boys hoarse.

(b) Secondary Sexual Characters are the characters which distinguish a boy from a girl. Characters like hair on chest, under the arms, development of breast, beard and moustaches etc. are all called secondary sexual characters.

(c) Sex determination in unborn baby: The sex of the unborn baby is determined by the sex chromosomes of the father. An unfertilized
egg always have X chromosome. If a sperm contributes X chromosome then the baby will be a female and if the sperm contributes Y chromosome, the baby will be a male. So it is the father, who is responsible for the sex of the unbomhaby.

Question 9.
Word game: Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone 10. Female hormone

Down
1. Male hormone
2. Secretes thyroxine
3. Another term for Teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence

Answer:

Question 10.
The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Age Year	Height (cm)
0	Boys	Girls
4	53	53
8	96	92
12	114	110
16	129	133
20	150	150

Answer:
We conclude that girl are taller than boys age of 12 yr. generally and there height is same at the age of 16 years but some boys gain height and generally become taller then girls.

Extended Learning – Activities And Projects

1. Find out from your elder relatives about their awareness of the leagal status of early marriage. You yourself may get information on it from your teacher, parents, a doctor or the internet. Write a two-minute speech explaining why early marriage is not good for the couple.
Answer:
The legal marriagable age for girls is 18 years and for boys it is 21 years. Before this age marriage is considered a crime. Early marriage is not good for couples because they are not prepared physically and mentally for the responsibilities of married life. A girl attains sexual maturity at age of about eighteen years. Before that her resproductive system is not fully prepared to bear a baby. Similarly boys are not capable of running the household as most of the boys at this age are pursuing their studies. So, the boys and girls should attain physical and mental maturity before getting married.

2. Collect newspaper cuttings and information in magazines about HIV/AIDS. Write a one page article of 15 to 20 sentences on HIV/AIDS.
Answer:
HIV/AIDS is a sexually transmitted diseased (STD) that means this diseases mostly spreads by sexual contacts with an HIV/AIDS infected persons. AIDS stands for Acquired Immunodeficiency Syndrome. It is created by HIV virus. This disease is a fatal disease for which no permanent treatement has been deviced by the scientists. AIDS is actually a disease which destroys the patients immune system slowly. The damage is most of the time permanent and beyond repair. Due to weak immunity the patient easily fall prey to many diseases which eventually kill the person.

Prevention is the only cure for HIV/AIDS. It is advised that one should maintain sexual hygiene and practice safe sexual relationship with a single partner.

3. In our country, according to a census, there are 882 adolescent femals for every 1000 males. Find out:
(a) the concerns of the community regarding this low ratio. Remember that the chance of having a boy or a girl is equal.
(b) what amniocentesis is and how useful this technique is. Why, is its use for indentification of sex of the unborn child banned in India l
Answer:
(a) The society is quite concerned about this issue. This is going to create a problem for them in future as it will become difficult for the boys to find girls for marriage.

(b) It is used to see, if all the organs of a feotus are developing well. It is banned in India to use this technique to determine the sex of the unborn child because they kill the female feotus to have baby boys in future. This is called female feoticide. The female feoticide has disturbed the ratio of boys and girls in India.

4. Put your ideas together and write a short note on the importance of knowing facts about reproduction.
For more information , visit:

• www.teenshealth.org/teen/sexual_health/
• www.ama_assn.org/ama/pub/category/ 1947.html
• www.adolescenthealth.com

Answer:
It is important to know facts about reproduction, because this phase i.e. reproduction phase has to come in every bodies life. It will help to handle all the physical and mental changes coming with sexual maturity in the bodies. It will also help in deciding one’s own course of life in future and save for many STDs.

HBSE 8th Class Science Reaching the Age of Adolescence Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is the phase of life when the body undergoes changes to attain reproductive maturity called?
Answer:
Adolescence.

Question 2.
What is the age period of adolescence?
Answer:
13 years to 18 years.

Question 3.
What is reproductive maturity called?
Answer:
Puberty.

Question 4.
Write any two changes in bodies of boys during adolescence.
Answer:
Increase in height, hairy line above lips.

Question 5.
What makes a person tall during adolescence?
Answer:
Elongated long bones of arms and legs.

Question 6.
What happens to voice box at puberty?
Answer:
It begins to grow.

Question 7.
What is the protruding part of the larynx visible in boy’s throat called?
Answer:
Adam’s Apple.

Question 8.
What changes occur in the voice of boy’s at the onset of puberty?
Answer:
It becomes hoarse.

Question 9.
Why do growing boys and girls get acnes or pimples?
Answer:
Due to increased secretions of sebacious glands.

Question 10.
What are those characters called, which distinguish a boy from a girl?
Answer:
Secondary sexual characters.

Question 11.
Give any one secondary sexual character of boys.
Answer:
Growth of moustaches and beard.

Question 12.
Give any one secondary sexual character of girls.
Answer:
Growth of breasts.

Question 13.
What controls the body changes during adolescence?
Answer:
Hormones.

Question 14.
What are hormones?
Answer:
Hormones are the chemical substances secreted by Endocrine glands.

Question 15.
Name the hormones secreted by testes.
Answer:
Testosterone.

Question 16.
Which hormone is secreted by ovaries 7
Answer:
Estrogen.

Question 17.
Which endocrine gland is called the master gland?
Answer:
Pituitary gland.

Question 18.
What are hormones secreted by testes and ovaries called collectively?
Answer:
Sex hormones.

Question 19.
Name the sex hormones secreted by testes and ovaries.
Answer:
Testosterone and Estrogen.

Question 20.
Name any one hormone secreted by Pituitary gland.
Answer:
Follicle stimulating Hormone or FSH.

Question 21.
Which hormone is responsible for the maturity of ova or sperms?
Answer:
Follicle stimulating hormone.

Question 22.
What is the common name given to ova and sperms?
Answer:
Gametes.

Question 23.
What is the beginning of menstruation called?
Answer:
Menarche.

Question 24.
What is the stoppage of menstruation called?
Answer:
Menopause.

Question 25.
What are the names given to sex chromosomes?
Answer:
X and Y.

Question 26.
Which sex chromosome determines the sex of body?
Answer:
Y Chromosome.

Question 27.
Which hormone is secreted by thyroid?
Answer:
Thyroxin.

Question 28.
Which hormone is secreted by pancreas?
Answer:
Insulin.

Question 29.
Which hormone controls the blood sugar level?
Answer:
Insulin.

Question 30.
Which hormone is secreted by Adrenal glands?
Answer:
Adrenalin.

Question 31.
Which hormone is called stress hormone?
Answer:
Adrenalin.

Question 32.
Why adrenalin is called stress hormone?
Answer:
Adrenalin is called stress hormone because it helps to calm down when one is angry.

Question 33.
What is a balanced diet?
Answer:
Diet containing all the necessary minerals in right proportion is called a balanced diet.

Question 34.
Name any food, which is called a balanced food in itself.
Answer:
Milk.

Question 35.
Which virus causes AIDS?
Answer:
HIV.

Short Answer Type Questions

Question 1.
What is adolescence?
Answer:
The phase of a person’s life, when his body undergoes changes to attain reproductive maturity is called adolescence. Adolescence begins at the age of 13 and lasts till the age of 18 or 19 years.

Question 2.
What are the signs of adolescence?
Answer:
Certain body changes mark the onset of puberty. Hairy line above lips in boys and sudden increase in height are the signs of puberty. In girls developing breasts show the on set of puberty.

Question 3.
Why some boys or girls have improportionate body parts during adolescence 7
Answer:
Some times the boys and girls have improportionate body parts. They look tall but face look smaller or other tilings. This is because all body parts do not grow at the same rate. But slowly they all catch up and body becomes balanced.

Question 4.
What changes take place in the body of adolescents during this period?
Answer:
Many changes take place in the bodies of boys and girls during adolescence. Their shoulders become wider and chest becomes broader. Girls get developed breasts and their hips become wider. Muscles of boys grow more than the girls.

Question 5.
What changes occur in the voice of boys and girls during puberty?
Answer:
The voice box or the larynx begins to grow. Boys have more grown voice box. It can be seen as the protrubed part in their throat.
Their voice becomes deep and sometimes, it grows more than controlled limit and their voice become hoarse. Girls get a high pitched voice.

Question 6.
What causes the changes in human body during puberty?
Answer:
The changes which occur during puberty are caused due to some chemical substances secreted by glands. These chemical substances are acalled Hormones. Endocrine system in human body has various glands, which secrete many important hormones which help the body to grow and mature.

Question 7.
How do sex hormones work in human body?
Answer:
In males the testosterone is secreted by testes and it causes growth of moustaches and beard. In girls estrogefi causes the development of mammary glands . They develop inside the breast and cause enlargement of breasts.

Question 8.
How does pituitary gland initiate the puberty in humans?
Answer:
Pituitary gland is called the master gland. It stimulates the testes and ovaries to produce sex hormones i.e. Testosterone and estrogen. These sex hormones further initiate the changes in body to attain sexual maturity.

Question 9.
What is menstruation?
Answer:
Monthly bleeding in women is called menstruation, when egg is matured and released by ovaries. It if not fertilized is dispelled by body along with the thick lining of uterus and with blood vessels. It is released from the body in form of monthly bleeding. It is called menstruation.

Question 10.
How the sex of the body is determined?
Answer:
Every human beings have 23 pairs of chromosomes in the nuclei of their cells. A pair of sex hormones are also among them. Females have XX sex chromosomes and males have XY sex chromosomes, when after fertilization the zygote get both X chromosomes from male and female, it will develop into a baby girl. When the zygote get X chromosome from female and Y from male, then it develops into a male. Thus the chromosome from a male decides if a baby will be a male or a female.

Long Answer Type Questions

Question 1.
What changes occur in body during puberty?
Answer:
Various changes occur in the body of human beings during puberty. These changes occur due to hormones secreted by reproductive organs. These changes are the following:
(a) Physical changes:
Various changes occur in the bodies of boys and girls. Boys get broader shoulders and wider chest. Sudden increase in their height is accompanied by growth of hair on their body parts. They get moustaches and beard.Girls get developed breasts and wider hips. More secretions from sweat and oil glands cause pimples and acnes in some young people.

(b) Change in Voice:
Voice of boys become deep due to enlarged larynx. Some time more growth in voice box is visible as Adam’s Apple in their throats. Their voice becomes even coarse in case of extra growth of larynx. Voice of girls become high pitched.

(c) Development of Sex Organs:
The reproductive organs of boys and girls become active. Testes start producing sperms and ovaries release matured eggs. Mental and Emotional Maturity: Young people become more mature mentally, emotionally and intellectually.

Question 2.
How are the changes of adolesence controlled by hormones?
Answer:
The endocrine system of body secretes many chemical substances which are directly poured into the blood stream, these chemical substances are called hormones. All changes taking place during adolescence are controlled by these hormones.

Pituitary glands secrete growth hormones which stimulates the sex organs to release hormones.. Testes start secreting testosterone and ovaries start secreting estrogen. These sex hormones cause secondary sexual characters. Estrogen causes development of mammary glands which develop under breast, thus breast starts enlarging in females.

Question 3.
How can bad habits like Drug addiction harm the young people?
Answer:
Boys and girls feel a little bit insecure and confused during adolescence due to sudden changes in their bodies. This can mislead them to certain unhealthy and immoral habbits, like drug addiction and many others. Drug addiction is a very bad habit which can spoil our lives. It is easy to start, taking drugs but very difficult to shun this habit. Drugs can cause many long term harms on our bodies.

They make our body weak and prone to many communicable diseases like AIDS and many other sexual disorders. AIDS virus HIV can pass on to a healthy person from an infected person by sharing the infected syringe. The drug addicts inject drugs by using syringe. The same syringe is shared by other addicts also, so the infected syringe can spread AIDS to others also.

Question 4.
Who is responsible to determine the sex of unborn baby: Father or mother?
Answer:
Each human being have 23 pairs of chromosomes in the nuclei of every cell. These chromosomes contain the hereditary information. Out of these chromosomes a pair of chromosome are called sex chromosomes, which are named X and Y Chromosomes. Each female has 2 X chromosomes while the males have one X chromosome and one Y chromosome. The unfertilized egg released by ovaries always have one X chromosome. Testes produce some sperms with X chromosome and some with Y chromosome.

If sperms with X chromosome fertilize with egg with unborn is a female, but if the sperms with Y chromosome fertilizes with egg, then the unborn baby will be a male. So, it becomes clear that it is the sperm released by father carrying X or Y chromosomes, that determines the sex of the unborn baby.

Question 5.
What should be done to maintain reproductive health?
Answer:
Following measures can help the young people to maintain their reproductive health.
(i) Balanced Diet:
Diet is very important for a growing body. Diet should be a balanced diet. Balanced diet contains all the necessary elements in required proportion. Elements like carbohydrates, proteins, fats and vitamins should be integral part of a balanced diet. Milk provides all the required elements in required proportion. Junk and fast food are good to taste but they are not nutritious so they should not be included in diet.

(b) Personal Hygiene:
One should keep one’s body clean by bathing everyday. All parts of the body should be washed properly because infections can take place due to more sweat and oil secretion by sweat and oil glands.

(c) Physical Exercise:
Daily routine of physical exercise can keep body fit and circulation of blood gets maintained providing energy to all parts of the body.

Reaching the Age of Adolescence Class 8 HBSE Notes

1. A baby becomes adult after passing a few development stages.
2. The age at which a child becomes capable of reproduction is called adolescence.
3. At the age of 11 years to 19 years a child reaches puberty.
4. Reproductive organs start developing as the puberty sets in.
5. Various changes occur in the bodies of boys and girls at age of puberty. Hair starts growing at different parts of body. Girls have developed breasts, heavy hips, boys get.moustaches and beard, their voice become heavy.
6. Height gain is prominent at age of puberty along with other changes. Hormones starts taking control of the reproductive organs, and make the beginning of maturity of reproductive organs.
7. Hormones are the chemical substances which are secreted by the pituitary glands directly into the blood stream.
8. Growth hormones stimulate other glands to secrete various other hormones to control various other body functions.
9. Various hormones secreted by different glands perform various functions. Ovaries and testes secrete hormones for sexual maturity, pancreas secrete Insulin to control sugar level, thyroid secret thyroxin and adrenal glands produce adrenalin. All these hormones are necessary for proper growth and development of body.
11. With onset of puberty females have hormones like estrogen. They have their uterine wall prepared to receive the fertilized egg. They have another phenomenon called menstruation. In this phenomenon they get the unfertilized egg flown out of body through blood.
12. Reproductive health needs a lot of care and one needs to maintain hygiene and physical activity.
13. Proper nutrition and balanced diet in necessary for growing body, so it should be taken care of.

Haryana State Board HBSE 8th Class Science Solutions Chapter 11 Force and Pressure Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 11 Force and Pressure

HBSE 8th Class Science Force and Pressure Textbook Questions and Answers

Question 1.
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Answer:
(i) We push the door to open it.
(ii) We pull the desk to change its position.

Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:
When we apply force on clay with our fingers, its shape gets changed, when we press balloon with our hands, its shape get changed.

Question 3.
Fill in the blanks in the following statements :
(a) To draw water from a well we have to _________ at the rope.
(b) A charged body _________ an uncharged body towards it.
(c) To move a loaded trolley we have to _________ it.
(d) The north pole of a magnet _________ the north pole of another magnet.
Answer:
(a) pull
(b) attracts
(c) push it
(d) repels.

Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the followiong terms:
muscular, contact, non-contact, gravity, friction, shape, attraction
(a) To stretch the bow, the archer applies a force that causes a change in its _________
(b) The force applied by the archer to stretch the bow is an example of _________ force.
(c) The type offeree responsible for a change in the state of motion of the arrow is an example of a _________ force.
(d) While the arrow moves towards its target, the forces acting on it are due to _________ and that due to _________ of air.
Answer:
(a) shape
(b) muscular
(c) contact
(d) gravity and friction.

Question 5.
In the following situations identify the agent exerting a force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer:
(a) Agent are fingers, object is lemon, effect of force can be observable in form of lemon juice being expelled by squeezing.

(b) Agent is hand of the person squeezing the tube, object is toothpaste tube and effect of the force can be observed’ as the paste coming out of the tube.

(c) Agent is the load suspended, object is the spring and effect can be seen in the form of elongation of spring on suspension of load.

Question 6.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
The force due to hammering causes the change in the shape of the iron and iron can be moulded in the shape of the required tool.

Question 7.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for, the attraction between the balloon and the wall?
Answer:
Electrostatic force.

Question 8.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer:
Forces acting on the plastic bucket are the muscular force and gravitational force. The forces do not bring the change in its state of motion because they are acting in opposite direction with equal magnitude. The effect of the gravitational force will pull it down if the muscular force will grow weak. The body will feel the stretch of gravitational force and will have to bend” to cancel the magnitude of gravitational force.

Question 9.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer:
Gravitational force and frictional force.

Question 10.
When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper.
The rise of water in the dropper is due to
(a) pressure of water
(b) gravity of the earth
(c) shape of rubber bulb
(d) atmospheric pressure
Answer:
(d) atmospheric pressure.

Extended Learning – Activities and Projects

Question 1.
Make a 50 cm x 50 cm bed of dry sand about 10 cm in thickness. Make sure that its top surface is levelled. Take a wooden or a plastic stool. Cut two strips of graph paper each with a width of 1 cm. Paste them vertically on any leg of the stool-one at the bottom and the other from the top. Now gently put the stool on the sand bed with its legs resting on the and Increase the size of sand bed if required. Now put a load, say a school bag full of books, on the seat of the stool. Mark the level of sand on the graph strip. This would give you the depth, if any, to which the legs of stool sink in sand. Next, turn the stool upside down so that now it rests on its seat on the sand bed. Note the depth to which the stool sinks now. Next, put the same load on the stool and note the depth to which it sinks in the sand. Compare the pressure exerted by the stool in the two situations.
Answer:
For self attempt.

Question 2.
Take a tumbler and fill it with water. Cover the mouth of the tumbler with a thick card similar to that of a postcard Hold the tumbler with one hand while keeping the card pressed to its mouth with your other hand. Turn the tumbler upside down while keeping the card pressed to its mouth. Make sure that the tumbler is held vertical.

Gently remove the hand pressing the card. What do you observe? Does the card get detached allowing the water to spill? With a little practice you will find that the card continues to hold water in the tumbler even after it is not supported by your hand. Also try this activity by using a piece of cloth to hold the tumbler in an upside down position.
Answer:
For self attempt.

Question 3.
Take 4-5 plastic bottles of different shapes and sizes. Join them together with small pieces of glass or rubber tube as shown in Fig. Keep this arrangement on a level surface. Now pour water in any one of the bottles.

Note whether the bottle in which water is poured gets filled first or all the bottle in which water is poured gets filled first or all the bottles get filled up simultaneously. Note the level of water in all the bottles from time to time. Try to explain your observations.
For more information on force and pressure visit:
→ www.glenbrook.kl2 .il.us/gbssci/phys/class/ newtlauws/u212a,html
→ www.hatesville.kl2.in.us/physics/phyNet/ Mechanics/Newton2/Pressure .html
→ www.kids.earth.nasa.gov/archive/ air_pressure/
Answer:
For self attempt.

Activities

Activity No. 11.1

Activity No. 11.5
Studying the Effect of Force on Objects

Very Short Answer Type Questions

Question 1.
Define force.
Answer:
Any push or pull is called force.

Question 2.
When does a body move?
Answer:
A body moves when force is applied.

Question 3.
What is the first requirement to put force into play?
Answer:
Interaction between two objects.

Question 4.
Give any example of push.
Answer:
Pushing a table to wall.

Question 5.
Give an example of pull.
Answer:
Pulling the door to shut.

Question 6.
When force is applied on the object in the same direction of motion, what happens?
Answer:
The speed will increase.

Question 7.
What will happen when force is applied in the direction opposite to the movement of object?
Answer:
The speed will decrease.

Question 8.
How is the strength of a force expressed?
Answer:
In magnitude.

Question 9.
What effect does force put of state of motion?
Answer:
The speed of the object may change.

Question 10.
What is the state of motion of an object?
Answer:
The speed and direction of an object is called state of motion.

Question 11.
Does the force change the direction of the moving object?
Answer:
Yes.

Question 12.
Does the force change the shape of the object?
Answer:
Yes.

Question 13.
What is the contact force?
Answer:
Force which comes in action when objects are in contact.

Question 14.
What is the muscular force?
Answer:
Force resulting due to action of muscles.

Question 15.
Give examples of muscular force.
Answer:
Bending, moving, kicking etc.

Question 16.
What kind of force is the muscular force?
Answer:
Contact force.

Question 17.
What is friction?
Answer:
Force acting equal and opposite to the moving object is friction.

Question 18.
What kind oi force is the friction?
Answer:
Contact force.

Question 19.
Give example of friction force.
Answer:
Stopping of a rolling ball.

Question 20.
Which force stops the moving striker on a carrom board?
Answer:
Friction.

Question 21.
Why does the soal of our shoes get torn away by walking?
Answer:
Due to friction between soal and road.

Question 22.
What are non-contact forces?
Answer:
Forces acting jrom distance without forming contact.

Question 23.
What is magnetic force?
Answer:
Force exerted by a magnet is called magnetic force.

Question 24.
What happens when similar poles of magnets come in contact?
Answer:
They repel each other.

Question 25.
What happens when opposite poles of magnets come in contact?
Answer:
They attract each other.

Question 26.
What is the electrostatic force?
Answer:
Force exerted by the charged bodies is called electrostatic force.

Question 27.
When a comb rubbed against hair is brought near the small pieces of paper, the paper attaches to the comb which force has attracted papers?
Answer:
Electrostatic force.

Question 28.
What kind of forces are magnetic force and electrostatic force?
Answer:
Non-contact forces.

Short Answer Type Questions

Question 1.
How do we feel force in our daily life?
Answer:
Many big or small actions make us feel the force. We have to push or pull many objects daily. A moving ball stops on its own, the ball changes the direction of its motion, when hits with a bat. We churn curd to make lassi and many other actions.

Question 2.
What is force? Define with example.
Answer:
Force is the pull or push of the objects. Actions like pushing, pulling, bending, running, lifting etc. are the examples of force. Moving or stopping or changing shape and direction of motion of objects are the various actions showing force in play.

Question 3.
What happens when two people push an object from same direction?
Answer:
When two people push or pull something together in same direction, the force applied by them get added and the action becomes easy.

Question 4.
How can force change the state of motion?
Answer:
Force can change the state of motion by changing the direction of the motion and by changing the speed of the motion. Force in the direction of the motion increases the speed and force in opposite direction decreases the speed.

Question 5.
What is the state of motion?
Answer:
State of motion of an object is its speed and its direction. State erf zero motion means state of rest. An object can be in two positions one at rest or at motion. Any change in this position can be the change in the state of motion.

Question 6.
What is muscular force? Why is it a contact force?
Answer:
The force exerted by the action of the muscles is called muscular force. Muscular activities like running, bending, walking etc. produce muscular force. Muscular force is a contact force because it is applied only when it is in contact with an object.

Question 7.
What is force of Motion? How does it arise?
Answer:
Force of friction is force opposite and equal to the force of moving body. Force of friction arises when there is a contact between two surfaces and some movement takes place in them. Force of friction is a contact force as it only arises when two surfaces come in contact with each other.

Question 8.
Why does a moving ball gradually come to rest?
Answer:
A moving bail comes to rest on its own due to force of friction. When ball moves on the ground, their surfaces come in contact to each other. The ball and the ground exert equal and opposite force on each other, which gradually brings the moving ball to a stop.

Question 9.
What is electrostatic force? What kind of a force is it?
Answer:
Electrostatic force is exerted by a charged body on another charged or uncharged body. For this it is not necessary for the two bodies to be in contact with each other. This force is applicable from a distance so it is a non-contact force.

Question 10.
What is pressure? What is the relation of pressure with area on which it is applied?
Answer:
Force exerted on per unit area is called pressure. Pressure is related with area on which it is applied. When the area is increased the pressure exerted is less. But when the area on which pressure is exerted is decrease the pressure increases. So we conclude that pressure increases with decrease in area.

Long Answer Type Questions

Question 1.
How will you prove that pressure of liquids decrease with increase in height ^ of its column?
Answer:
For this to be proven take aplastic

container. Take a pin and make holes in the container in horizontal line from bottom to middle of the container. Now put water in the container and observe, you will see the water will come out with maximum pressure while the hole at the top will have the minimum pressure of water.

Question 2.
What changes are caused dud to application of farce on object?
Answer:
Force when applied on an object cause many changes on the object. Following changes occur due to application of force:
(i) Force change the state of motion : Force can change the state of motion of the object. It can increase or decrease the speed of the moving object. It can change the direction of the moving object.

(ii) Force can change the shape of the object: Force can change the shape of the object on which it is applied. When force is applied on some object, it always have some effect on the shape of the object. The change in the object is some time visible and some time, it is pot visible, but change in shape of the object is always accompanied by application of force.

Question 3.
What are the contact forces? Explain different forces which are contact forces.
Answer:
Contact forces are the forces which come in play when two objects come in contact with each other. Following forces are the contact forces :
(i) Muscular Force : The force which is exerted due to action of muscles is called muscular force. Actions like bending, running, moving etc. are examples of muscular forces. It is a contact force because it comes in play when it comes in contact of the object.

(ii) Friction: Equal and opposite force being exerted on an object when its surface comes in contact with other surface. It is also a contact force because it is exerted when two surfaces come in contact with each other Halting of a moving ball on its own is an example of force of friction.

Question 4.
What are the non-contact forces? Explain different non-contact forces.
Answer:
Non-contact forces are those forces, which can be exerted from a distance without establishing a contact. Following forces are the non-contact forces :
(i) Magnetic force : Force exerted by a magnet on another magnet or magnetic substance like iron is called magnetic force. Like poles of a magnet repel each other and opposite poles of a magnet attract each other.

(ii) Electrostatic Force: Force exerted by a charged body on other charged body or uncharged body is called electrostatic force. If we rub a comb with our hair and bring it near some small bits of paper, it will attract the bits of paper towards itself. This is electrostatic force which acts without making a direct contact with other charged or uncharged object.

(iii) Force of Gravity : Earth pulls every freely falling object towards its centre. This force exerted by earth is called force of gravity. This is also a non-contact force as it acts from a distance.

Force and Pressure Class 8 HBSE Notes

• Every push or pull is called force.
• Force comes into action when an object interacts with other object.
• Forces when implied in same direction add to each other, but when applied in opposite directions, they cancel each other. Equal forces applied in opposite direction results in net zero force.
• Force has magnitude and direction.
• Force can bring many changes in body on which it is applied.
• Force can change the speed of the moving body. Force in same direction of motion can increase the speed and in opposite direction can decrease the speed.
• Force can change the direction of the object in motion or at rest.
• Force can change theshapeof theobject. Force when applied on an object is always accompanied by change’in its shape.
• Two objects when come in contact with each other, they apply force on each other, this is called contact force. Muscular force, friction force etc. are examples of contact force.
• Force acting opposite to the direction of motion of a moving object is called force of friction.
• Force which acts from a distance is called a non-contact force.Magnetic force, electrostatic force and gravitational force are the examples of non-contact force.
• Force exerted per unit area is called pressure.
• Liquids and gases also exert pressure in all directions.
• Pressure exerted by air is called atmospheric pressure.