Class 7

Haryana State Board HBSE 7th Class Maths Solutions Chapter 12 बीजीय व्यंजक InText Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 12 बीजीय व्यंजक InText Questions

प्रयास कीजिए (पृष्ठ सं. 246)

प्रश्न 1.
बताइए कि निम्नलिखित व्यंजक किस प्रकार प्राप्त किए जाते हैं :
7xy + 5, x²y, 4x² – 5x
हल :
7xy + 5 में, पहले हमें xy प्राप्त होता है। इसको 7 से गुणा करने पर 7xy प्राप्त होता है और 7xy में 5 जोड़ने पर 7xy + 5 प्राप्त होता है।
x²y में, पहले हमें x2 प्राप्त होता है। इसमें का गुणा करने पर x²y प्राप्त होता है।
4x² – 5y में, पहले हमें x2 प्राप्त होता है और इसे 4 से गुणा करने पर 4x² प्राप्त होता है और दूसरे पद को प्राप्त करने के लिए y को 5 से गुणा करके 4x² में से घटाने पर 4x² – 5y प्राप्त होता है।

पृष्ठ सं. 247

प्रश्न 1.
निम्नलिखित व्यंजकों में कौन-कौन से पद हैं ? दर्शाइए कि ये व्यंजक कैसे बनाए जाते हैं। प्रत्येक व्यंजक के लिए एक पेड़ आरेख भी खींचिए-
8y + 3x², 7mn – 4, 2x²y
हल :
8y + 3x² में 8y और 3x² पद हैं।
पद 8y, स्थिरांक 8 और y गुणा करने से प्राप्त होता है।
पद 3x², 3, x और x को गुणा करने से प्राप्त होता है।
इसका पेड़ आरेख निम्न है-

7mn – 4 में, 7mn और (-4) पद हैं।
7mn प्राप्त करने के लिए हम चर m, n को 7 से गुणा करते हैं।
(-4) प्राप्त करने के लिए पूर्णांक (-4) लेंगे।
इसका पेड़ आरेख निम्न है-

2x²y में, एक ही पद 2x²y है।
2x²y में, पहले हम x² प्राप्त करते हैं। इसको y से गुणा करके x²y प्राप्त करते हैं। इसे 2 से गुणा करने पर 2x²y प्राप्त होता है।
इसका पेड़ आरेख निम्न है-

प्रश्न 2.
ऐसे तीन व्यंजक लिखिए, जिनमें से प्रत्येक में चार पद हों।
हल :
चार पदों वाले तीन व्यंजक
3x + 2y + z – 7, 2x² – 5y³ + z + 2, xy + yz + zx + 5

पृष्ठ सं. 248

प्रश्न 1.
निम्नलिखित व्यंजकों के पदों के गुणांकों की पहचान कीजिए :
4x – 3y, a + b + 5, 2y + 5, 2xy.
हल :
4x – 3y में,
4x में x का गुणांक 4 है।
-3y में का गुणांक – 3 है।

a + b + 5 में,
a का गुणांक 1 है।
b का गुणांक 1 है।

2y + 5 में,
2y में y का गुणांक 2 है।

2xy में,
2xy में xy का गुणांक 2 है।
2xy में y का गुणांक 2x है।
2xy में x का गुणांक 2y है।

पृष्ठ सं. 249

प्रश्न 1.
निम्नलिखित में, समान पदों के समूह बनाइए :
12x, 12, – 25x, – 25, – 25y, 1, x, 12y, y.
हल :
समान पदों के समूह :
12x, – 25x, x; 12, – 25, 1; -25y, 12y, y.

पृष्ठ सं. 250

प्रश्न 1.
निम्नलिखित व्यंजकों को एकपदी, द्विपद और त्रिपद के रूप में वर्गीकृत कीजिए :
a, a + b, ab + a + b, ab + a + b – 5, xy, xy + 5, 5x² – x + 2, 4pq – 3q + 5p, 7, 4m – 7n + 10, 4mn +7.
हल :
एक पदी : a, xy और 7.
द्विपद : a + b, xy + 5 और 4mn + 7
त्रिपद : ab + a + b, 5x² – x + 2, 4pq – 3q + 5p और 4m – 7n + 10.

पृष्ठ सं. 253

प्रश्न 1.
कम-से-कम ऐसी दो स्थितियों के बारे में सोचिए जिनमें से प्रत्येक में आपको दो बीजीय व्यंजकों को बनाने की आवश्यकता पड़े और उन्हेंजोड़ना या घटाना पड़े।
हल :
प्रथम स्थिति : A व्यक्ति के पिता का भार, A के भार से 3 गुना है।
A व्यक्ति के नाना का भार A के भार और A के पिता के भार के योग से 5 किग्रा अधिक है। आप A व्यक्ति के नाना का भार कैसे ज्ञात करोगे?

द्वितीय स्थिति : दो ट्रेन एक ही स्टेशन से विपरीत दिशाओं में चलना प्रारम्भ करती है। एक को औसत चाल दूसरी ट्रेन की औसत चाल से 15 किमी प्रति घंटा कम है। यदि 3 घण्टे बाद उनके बीच की दूरी 1800 किमी हो तो आप उनकी औसत चाल कैसे ज्ञात करोगे ?

पृष्ठ सं. 255

प्रश्न 1.
जोड़िए और घटाइए :
(i) m – n, m + n
(ii) mn + 5 – 2, mn + 3
हल :
(i) (m – n) + (m + n)
= m – n + m + n
= m + m – n + n
= (1 + 1)m + (-1 + 1)n
= 2m + 0n
= 2m + 0 = 2m
और (m – n) – (m + n) = m – n – m – n
= m – m – n – n
= (1 – 1)m + (- 1 – 1)n
= 0m + (-2)n
= 0 – 2n = – 2n

(ii) (mn + 5 – 2) + (mn + 3)
= (mn + 3) + (mn + 3)
= 2mn + 6
(mn + 5 – 2) – (mn + 3)
= (mn + 3) – (mn + 3) = 0

पृष्ठ सं. 261

प्रश्न 1.
दर्शाए गए आधारभूत आकारों को लेकर उपर्युक्त प्रकार के पैटर्न बनाइए:

[आकारों को बनाने के लिए आवश्यक रेखाखण्डों की संख्या दाईं ओर लिखी हुई है। साथ ही n आकारों को बनाने के लिए आवश्यक रेखाखण्डों के दर्शाने वाला व्यंजक भी दाईं ओर दिया हुआ है।]
आगे बढ़िए और ऐसी ही और पैटनों की खोज कीजिए।
हल :
आगे के पैटर्न इस प्रकार होंगे-

Haryana State Board HBSE 7th Class Maths Solutions Chapter 2 भिन्न एवं दशमलव InText Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 2 भिन्न एवं दशमलव InText Questions

प्रयास कीजिए (पृष्ठ सं. 34)

प्रश्न 1.
हल कीजिए : 3 × \(\frac {8}{7}\) = ?, 4 × \(\frac {7}{5}\) = ?
हल:
3 × \(\frac{8}{7}=\frac{3 \times 8}{7}=\frac{24}{7}\)
4 × \(\frac{7}{5}=\frac{4 \times 7}{5}=\frac{28}{5}\)

पृष्ठ सं. 34

प्रश्न 2.
ज्ञात कीजिए:
(a) \(\frac {2}{7}\) × 3
(b) \(\frac {9}{7}\) × 6
(c) 3 × \(\frac {1}{8}\)
(d) \(\frac {13}{11}\) × 6
यदि गुणनफल एक विषम भिन्न है, तो इसे मिश्रित भिन्न के रूप में व्यक्त कीजिए।
हल :

प्रश्न 3.
2 × \(\frac{2}{5}=\frac{4}{5}\) = को सचित्र निरूपित कीजिए।
हल :
2 × \(\frac{2}{5}=\frac{4}{5}\) को निम्न प्रकार चित्र द्वारा व्यक्त कर सकते हैं :

पृष्ठ सं. 34

प्रश्न 4.
ज्ञात कीजिए :
(i) 5 × 2 \(\frac {3}{7}\)
(ii) 1\(\frac {4}{9}\) × 6
हल :

पृष्ठ सं. 35

प्रश्न 1.
क्या आप बता सकते हैं कि:
(i) 10 का \(\frac {1}{2}\)
(ii) 16 का \(\frac {1}{4}\)
(iii) 25 का \(\frac {2}{5}\) क्या है?
हल :

पृष्ठ सं. 39

प्रश्न 1.
निम्नलिखित बक्सों को भरिए।
हल :

पृष्ठ सं. 40

प्रश्न 1.
ज्ञात कीजिए :
\(\frac{2}{3} \times \frac{4}{5}\), \(\frac{2}{3} \times \frac{1}{5}\)
हल :
\(\frac{2}{3} \times \frac{4}{5}=\frac{2 \times 4}{3 \times 5}=\frac{8}{15}\)
\(\frac{2}{3} \times \frac{1}{5}=\frac{2 \times 1}{3 \times 5}=\frac{2}{15}\)

प्रश्न 2.
ज्ञात कीजिए :
\(\frac{8}{3} \times \frac{4}{7} ; \frac{3}{4} \times \frac{2}{3}\)
हल:
\(\frac{8}{3} \times \frac{4}{7}=\frac{8 \times 4}{3 \times 7}=\frac{32}{21}\)
\(\frac{3}{4} \times \frac{2}{3}=\frac{3 \times 2}{4 \times 3}=\frac{6}{12}\)

पृष्ठ सं. 45

प्रश्न 1.
ज्ञात कीजिए :
(i) 7 ÷ \(\frac {2}{5}\)
(ii) 6 ÷ \(\frac {4}{7}\)
(iii) 2 ÷ \(\frac {8}{9}\)
हल :
हम जानते हैं कि किसी पूर्ण संख्या को एक भिन्न से भाग करने के लिए उस पूर्ण संख्या को उस भिन्न के व्युत्क्रम से गुणा करते हैं।

प्रश्न 2.
ज्ञात कीजिए:
(i) 6 ÷ 5\(\frac {1}{3}\)
(ii) 7 ÷ 2\(\frac {4}{7}\)
हल :

पृष्ठ सं. 46

प्रश्न 1.
ज्ञात कीजिए:
(i) \(\frac{3}{5} \div \frac{1}{2}\)
(ii) \(\frac{1}{2} \div \frac{3}{5}\)
(iii) 2\(\frac{1}{2} \div \frac{3}{5}\)
(iv) 5\(\frac{1}{6} \div \frac{9}{2}\)
हल :

पृष्ठ सं. 51

प्रश्न 1.
ज्ञात कीजिए:
(i) 2.7 × 4
(ii) 1.8 × 1.2
(iii) 2.3 × 4.35
हल :
(i) 27 × 4 = 108
अतः 2.7 × 4 = 10.8
(ii) 18 × 12 =216
अत: 1.8 × 1.2 = 2.16
(iii) 23 × 435 = 10005
अत: 2.3 × 4.35 = 10.005

प्रश्न 2.
प्रश्न 1 में प्राप्त गुणनफलों को अवरोही क्रम में क्रमबद्ध कीजिए।
हल :
10.8, 2.16 और 10.005 को अवरोही क्रम में लिखने पर,
10.005 > 2.16 (∵ 10 > 2)
10.8 और 10.005 में,
10.8 > 10.005, (∵ 0.8 > 0.005)
अतः 10.8 > 10.005 > 2.16.

पृष्ठ सं. 52

प्रश्न 1.
ज्ञात कीजिए:
(i) 0.3 × 10
(ii) 1.2 × 100
(iii) 56.3 × 1000
हल :
(i) 0.3 × 10 = 3
(ii) 1.2 × 100 = 120
(iii) 56.3 × 1000 = 56300

पृष्ठ सं. 53

प्रश्न 1.
ज्ञात कीजिए:
(i) 235.4 ÷ 10
(ii) 235.4 ÷ 100
(iii) 235.4 ÷ 1000
हल :
(i) 235.4 ÷ 10 = 23.54
(ii) 235.4 ÷ 100 = 2.354
(iii) 235.4 ÷ 1000 = 0.2354

पृष्ठ सं. 54

प्रश्न 1.
(i) 35.7 ÷ 3 = ?
(ii) 25.5 ÷ 3 = ?
हल :

प्रश्न 2.
(i) 43.15 ÷ 5 = ?
(ii) 82.44 ÷ 6 = ?
हल:

पृष्ठ सं. 55

प्रश्न 1.
(i) 15.5 ÷ 5 = ?
(ii) 126.35 ÷ 7 = ?
हल :

पृष्ठ सं. 56

प्रश्न 1.
ज्ञात कीजिए:
(i) \(\frac{7.75}{0.25}\)
(ii) \(\frac{42.8}{0.02}\)
(iii) \(\frac{5.6}{1.4}\)
हल :

Haryana State Board HBSE 7th Class Maths Solutions Chapter 14 सममिति Ex 14.3 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 14 सममिति Ex 14.3

प्रश्न 1.
किन्हीं दो आकृतियों के नाम बताइए, जिनमें रैखिक सममिति और क्रम 1 से अधिक की घूर्णन सममिति दोनों ही हों।
हल :
दो आकृतियाँ निम्न होंगी-

1. समबाहु त्रिभुज
2. एक वृत्त।

प्रश्न 2.
जहाँ सम्भव हो, निम्नलिखित की एक रफ आकृति खींचिए :
(i) एक त्रिभज, जिसमें रैखिक सममिति और क्रम 1 से अधिक की घूर्णन सममिति दोनों ही हों।
(ii) एक त्रिभुज, जिसमें केवल रैखिक सममिति और क्रम 1 से अधिक की घूर्णन सममिति न हो।
(iii) एक चतुर्भुज जिसमें क्रम 1 से अधिक की घूर्णन सममिति हो, परन्तु रैखिक सममिति न हो।
(iv) एक चतुर्भुज जिसमें केवल रैखिक सममिति हो और क्रम 1 से अधिक की घूर्णन सममिति न हो।
हल :
प्रत्येक स्थिति की एक आकृति निम्न है-
(i)

तीन रैखिक सममिति

(ii) एक रैखिक सममिति लेकिन कोई भी घूर्णन सममिति क्रम 1 से अधिक नहीं।

(iii) कोई रैखिक सममिति नहीं लेकिन क्रम 2 की घूर्णन सममिति।

(iv) एक रैखिक सममिति लेकिन कोई घूर्णन सममिति नहीं।

प्रश्न 3.
यदि किसी आकृति की दो या अधिक सममित रेखाएँ हों, तो क्या यह आवश्यक है कि उसमें क्रम 1 से अधिक की घूर्णन सममिति होगी ?
हल :
जब किसी आकृति की दो या अधिक रैखिक सममिति होती हैं तो आकृति में क्रम 1 से अधिक घूर्णन सममिति होती है।

प्रश्न 4.
रिक्त स्थानों को भरिए :

हल :
रिक्त स्थानों की पूर्ति करने पर,

प्रश्न 5.
ऐसे चतुर्भुजों के नाम बताइए, जिसमें रैखिक सममिति और क्रम 1 से अधिक की घूर्णन सममिति दोनों ही हों।
हल :
ऐसे चतुर्भुजों जिनमें रैखिक सममिति और क्रम 1 से अधिक घूर्णन सममिति दोनों ही हों, वह वर्ग होगा।

प्रश्न 6.
किसी आकृति को उसके केन्द्र के परितः 60° के कोण पर घुमाने पर, वह उसकी प्रारम्भिक स्थिति जैसी ही दिखाई देती है। इस आकृति के लिए ऐसे कौन-से अन्य कोणों के लिए भी हो सकता है ?
हल :
अन्य कोण निम्न होंगे :
120°, 180°, 240°, 300°, 360°.

प्रश्न 7.
क्या हमें कोई ऐसी क्रम 1 से अधिक की घूर्णन सममिति प्राप्त हो सकती है, जिसके घूर्णन के कोण निम्नलिखित हों ?
(i) 45°
(ii) 17°
हल :
(i) हाँ
(ii) नहीं।

Haryana State Board HBSE 7th Class Maths Solutions Chapter 14 सममिति Ex 14.2 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 14 सममिति Ex 14.2

प्रश्न 1.
निम्नलिखित आकृतियों में से किन आकृतियों में 1 से अधिक क्रम की घूर्णन सममिति है ?

हल :
आकृति (a), (b), (d), (e) और (f) में क्रम 1 से अधिक घूर्णन सममिति है।

प्रश्न 2.
प्रत्येक आकृति के घूर्णन सममिति का क्रम बताइए।

हल :
माना प्रत्येक आकृति पर बिन्दु A और कोण जिस पर घूर्णन करेगा अंकित किया तथा घूर्णन निम्न प्रकार होगा-

घूर्णन सममिति ज्ञात करना :
आकृति (a) में, इसमें दो घूर्णनों की आवश्यकता होती है। प्रत्येक घूर्णन 180° के कोण के द्वारा हो जो (X) के परितः घूमने पर प्रारम्भिक स्थिति में वापिस आ जाएगा। अतः इसमें क्रम 2 की घूर्णन सममिति होगी।

आकृति (b) में, इसमें दो घूर्णनों की आवश्यकता होती है। प्रत्येक घूर्णन 180° के कोण द्वारा हो जो (×) के परितः घूमने पर प्रारम्भिक स्थिति में वापिस आ जाएगा। अतः इसमें क्रम 2 की घूर्णन सममिति होगी।

आकृति (c) में, त्रिभुज में तीन घूर्णन प्रत्येक 120° के कोण की आवश्यकता होती है जो (×) के परितः घूमने पर प्रारम्भिक स्थिति में वापिस आ जाएगा। अतः इसमें क्रम 3 की घूर्णन सममिति होगी।

आकृति (d) में, आकृति में 4 घूर्णन प्रत्येक 90° के कोण की आवश्यकता होगी जो (×) के परितः घूमने पर प्रारम्भिक स्थिति में वापिस आ जाएगा। अतः इसमें क्रम 4 की घूर्णन सममिति होगी।

आकृति (e) में, आकृति में 4 घूर्णन प्रत्येक 90° के कोण की आवश्यकता होगी जो (×) के परितः घूमने पर प्रारम्भिक स्थिति में वापिस आ जाएगा। अतः इसमें क्रम 4 की घूर्णन सममिति होगी।

आकृति (f) में, समपंचभुज में 5 घूर्णन प्रत्येक 72° के कोण की आवश्कयता होगी जो (×) के परितः घूमने पर वापस प्रारम्भिक स्थिति में आ जाएगा। अतः इसमें क्रम 5 की घूर्णन सममिति होगी।

आकृति (g) में, आकृति में 6 घूर्णन प्रत्येक 60° के कोण की आवश्यकता होगी जो (×) के परितः घूमने पर वापिस अपनी प्रारम्भिक स्थिति में आ जाएगा। अतः इसमें क्रम 6 की घूर्णन सममिति होगी।

आकृति (h) में, आकृति में 3 घूर्णन प्रत्येक 120° के कोण की आवश्यकता होगी जो (×) के परितः घूमने पर वापिस अपनी प्रारम्भिक स्थिति में आ जाएगा। अतः इसमें क्रम 3 की घूर्णन सममिति होगी।

Haryana State Board HBSE 7th Class Maths Solutions Chapter 15 ठोस आकारों का चित्रण Ex 15.3 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 15 ठोस आकारों का चित्रण Ex 15.3

प्रश्न 1.
आपको कौन-सा अनुप्रस्थ-काट प्राप्त होती है, जब आप निम्नलिखित ठोसों को
(i) ऊर्ध्वाधर रूप से और
(ii) क्षैतिज रूप से काटते हैं ?
(a) एक ईंट
(b) एक गोल सेब
(c) एक पासा
(d) एक बेलनाकार पाइप
(e) एक आइसक्रीम शंकु
हल:

Haryana State Board HBSE 7th Class Maths Solutions Chapter 15 ठोस आकारों का चित्रण Ex 15.2 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 15 ठोस आकारों का चित्रण Ex 15.2

प्रश्न 1.
एक समदूरीक बिन्दुकित कागज का प्रयोग करते हुए, निम्नलिखित आकृतियों में से प्रत्येक का एक समदूरीक चित्र खींचिए :

हल :
प्रत्येक आकार की एक समदूरीक आकृति निम्न प्रकार है

प्रश्न 2.
किसी घनाभ की विमाएँ 5 सेमी, 3 सेमी और 2 सेमी हैं। इस घनाभ के तीन भिन्न-भिन्न समदूरीक चित्र खींचिए।
हल :
घनाभ जिसकी विमाएँ 5 सेमी, 3 सेमी और 2 सेमी हैं। इस घनाभ के तीन समदूरीक चित्र निम्न प्रकार हैं-

प्रश्न 3.
2 सेमी किनारों वाले तीन घनों को परस्पर सटाकर रखते हुए एक घनाभ बनाया गया है। इस घनाभ का एक तिर्यक अथवा एक समदूरीक चित्र खींचिए।
हल :
2 सेमी किनारे वाले घनों को परस्पर सटाकर रखते हुए एक समदूरीक घनाभ चित्र निम्न प्रकार बनाया जाता है-

प्रश्न 4.
निम्नलिखित समदूरीक आकारों में से प्रत्येक के लिए, एक तिर्यक चित्र खींचिए :

हल :
तिर्यक चित्र निम्न प्रकार है-

प्रश्न 5.
निम्नलिखित में से प्रत्येक के लिए, (i) एक तिर्यक चित्र और (ii) एक समदूरीक चित्र खींचिए-
(a) 5 सेमी, 3 सेमी और 2 सेमी विमाओं वाला एक घनाभ (क्या आपका चित्र अद्वितीय है ?)
(b) 4 सेमी लम्बे किनारे वाला एक घन।
हल :
(a) (i) 5 सेमी, 3 सेमी और 2 सेमी विमाओं वाले घनाभ का तिर्यक चित्र दर्शाया गया है।

यह चित्र अद्वितीय नहीं है।

(ii) घनाभ का समदूरीक चित्र

(b) (i) 4 सेमी किनारे वाले घन का तिर्यक चित्र :

(ii) घन का समदूरीक चित्र :

Haryana State Board HBSE 7th Class Maths Solutions Chapter 2 भिन्न एवं दशमलव Ex 2.3 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 2 भिन्न एवं दशमलव Ex 2.3

प्रश्न 1.
ज्ञात कीजिए :
(i) (a) \(\frac {1}{4}\) का \(\frac {1}{4}\)
(b) \(\frac {3}{5}\) का \(\frac {1}{4}\)
(c) \(\frac {4}{3}\) का \(\frac {1}{4}\)

(ii) (a) \(\frac {2}{9}\) का \(\frac {1}{7}\)
(b) \(\frac {6}{5}\) का \(\frac {1}{7}\)
(c) \(\frac {3}{10}\) का \(\frac {1}{7}\)
हल :

प्रश्न 2.
गुणन कीजिए और न्यूनतम रूप में बदलिए (यदि सम्भव है):

हल :

प्रश्न 3.
निम्नलिखित भिनों को गुणा कीजिए :

हल :

प्रश्न 4.
कौन बड़ा है ?
(i) \(\frac {22}{7}\) का \(\frac {22}{7}\) अथवा \(\frac {22}{7}\) का \(\frac {22}{7}\)
(ii) \(\frac {22}{7}\) का \(\frac {22}{7}\) अथवा \(\frac {22}{7}\) का \(\frac {22}{7}\)
हल :

प्रश्न 5.
सैली अपने बगीचे में चार छोटे पौधे एक पंक्ति से लगाती है। दो क्रमागत छोटे पौधों के बीच की दूरी \(\frac {3}{4}\) मीटर है। प्रथम एवं अंतिम पौधे के बीच की दूरी ज्ञात कीजिए।
हल :
मांना चार पेड़ A, B, C, D इस प्रकार हैं कि
AB = BC = CD = \(\frac {3}{4}\) मीटर

∴ पहले और अन्तिम पेड़ के बीच की दूरी
= AD = 3 × AB
= 3 × \(\frac{3}{4}=\frac{9}{4}=2 \frac{1}{4}\) मीटर। उत्तर

प्रश्न 6.
लिपिका एक पुस्तक को प्रतिदिन 1\(\frac {3}{4}\) घण्टे पढ़ती है। वह सम्पूर्ण पुस्तक को 6 दिनों में पढ़ती है। उस पुस्तक को पढ़ने में उसने कुल कितने घण्टे लगाए ?
हल:
1 दिन में पढ़ती है = 1\(\frac {3}{4}\) घण्टे
पूरी पुस्तक को पढ़ने में लिए = 6 दिन
अत: 6 दिन में कुल समय चाहिए
(6 × 1\(\frac {3}{4}\)) घण्टे = 6 × \(\frac{(1 \times 4+3)}{4}\) घण्टे
\(\frac{6 \times(4+3)}{4}\) घण्टे = \(\frac{6 \times 7}{4}=\frac{42}{4}\) घण्टे
= \(\frac {21}{2}\) घण्टे = 10\(\frac {1}{2}\) घण्टे = 10 घण्टे 30 मिनट। उत्तर

प्रश्न 7.
एक कार 1 लीटर पैट्रोल में 16 किमी दौड़ती है। लीटर पैट्रोल में यह कार कुल कितनी दूरी तय करेगी?
हल :
कार 1 लीटर पैट्रोल में चलती है = 16 किमी
∴ 2\(\frac {3}{4}\) लीटर पैट्रोल में चलेगी = (16 × 2\(\frac {3}{4}\)) किमी
= 16 × \(\frac{(2 \times 4+3)}{4}\) = 16 × \(\frac{(8+3)}{4}\)
= 16 × \(\frac {11}{4}\) = 4 × 11 = 44 किमी। उत्तर

प्रश्न 8.

हल :

Haryana State Board HBSE 7th Class Science Solutions Chapter 6 Physical and Chemical Changes Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 6 Physical and Chemical Changes

HBSE 7th Class Science Physical and Chemical Changes Textbook Questions and Answers

Question 1.
Classify the changes involved in the following processes as physical or chemical changes.
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f) Digestion of food.
Answer:
Physical Change (b), (d), (e)
Chemical Change (a), (c), (f)

Question 2.
State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
(a) Cutting a log of wood into pieces is a chemical change.
(b) Formation of manure from leaves is a physical change.
(c) Iron pipes coated with zinc do not get rusted easily.
(d) Iron and rust are the same substances.
(e) Condensation of steam is not a chemical change.
Answer:
(a) False
(b) False
(c) True
(d) True
(e) True.

Question 3.
Fill the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of ………….. .
(b) The chemical name of baking soda is ……………… .
(c) Two methods by which rusting of iron can be prevented are …………. and …………. .
(d) Changes in which only …………. properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called …………. changes.
Answer:
(a) Calcium carbonate
(b) Sodium hydrogen carbonate
(c) Coating, galvanization
(d) Physical
(e) Chemical.

Question 4.
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Answer:
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas carbon dioxide.
lemon juice + baking soda → carbon dioxide + lime water
Since, a change in which one or more new substance are formed is called a chemical change, therefore this is a chemical change.

Question 5.
When a caùdie burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
Answer:
Physical Change → Melting of ware
Chemical Change → Burning of candle

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
The conversion of milk into curd, i.e., setting of curd is a permanent as well as irreversible and lead to the production of a new substance. The new substance, curd is formed has different composition and properties from the milk. Hence, setting of curd is a chemical change.

Question 7.
Explain why burning of wood is cutting it into small pieces are considered as two different types of a changes.
Answer:
Burning of wood is a chemical change because, in addition to new products burning is always accompanied by production of heat.
Cutting of wood into small pieces is a physical change because, pieces of wood underwent changes in size and no new substance is formed.

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
Take a cup full of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling add copper sulphate powder slowly while stirring continuously. Continue adding copper sulphate powder till no more powder can be dissolved. Filter the solution. Allow it to cool. Do not disturb the solution when it is cooling. Look at the solution after some time. Now, you can see the crystals of copper sulphate.

Question 9.
Explain how painting of an iron gate prevents it from rusting.
Answer:
The process of rusting can be represented by the following equation:
Iron (Fe) + Oxygen (O₂ from the air) + Water (H₂O) → rust (iron oxide Fe₂O₃).

For rusting the presence of both oxygen and water (or water vapour) is essential. In fact, if the content of moisture in air is high, which means if it is more humid, rusting becomes faster. So, prevent iron gate from coming in contact with oxygen, or water, or both. One simple way is to apply a coat of paint or grease. In fact, these coats should be applied regularly to prevent rusting.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
The water of coastal areas contain many salts. The salt water makes the process of rust formation faster. Thus, rusting of iron objects is faster in coastal areas than deserts.

Question 11.
The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both process A and B are chemical changes.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change,
(ii) Process – B is a chemical change.
(iii) Both process A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both process A and B are chemical changes.

Extended Learning – Activities And Projects

Question 1.
Take three glass bottles with wide mouths. Label them A, B and C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil of the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.
Answer:
Do yourself.

Question 2.
Prepare crystals of alum.
Answer:
Do yourself.

Question 3.
Collect information about the types of fuels used for cooking in your area. Discuss with your teachers/parents/others which fuels are less polluting and why.
Answer:
Do yourself.

HBSE 7th Class Science Physical and Chemical Changes Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is a physical change?
Answer:
Change in which no new product is formed.

Question 2.
What is a chemical change?
Answer:
A change in which a new substance with different properties is formed.

Question 3.
Which of the following substance contains only one kind of atoms?
copper, iron, iron sulphide, sulphur, oxygen gas, water, air and hydrogen gas.
Answer:
The following contains only one kind of atoms:
Copper, Iron, Sulphur, Oxygen gas, Hydrogen gas.

Question 4.
Which of the following substances are compounds and which are elements?
Magnesium oxide, Mercuric oxide, Carbon, Nitrogen, Potassium permagnate, Sodium carbonate.
Answer:
Elements: Carbon, nitrogen.
Compounds: Magnesium oxide, mercuric oxide, potassium permanganate, Sodium carbonate.

Question 5.
Write the symbol of the following elements:
Aluminium, calcium, chlorine, cobalt, iodine and mercury.
Answer:
Al, Ca, Cl, Co, I, Hg.

Question 6.
Ne is the symbol of neon. What else does it represent?
Answer:
This symbol represent one atom of Neon.

Question 7.
Which elements are represented by the following symbols?
Na, K, P, Pb, Ca, Zn, Br, Sn.
Answer:
Sodium, Potassium, Phosphorus, Calcium, Zinc, Bromine, Tin.

Question 8.
Name four Elements which occur in gaseous form.
Answer:
Oxygen, Nitrogen, Hydrogen and Argon.

Question 9.
When some one open a bottle of perfumes, you smell it from a distance why it is so?
Answer:
It is due to the property of gases that their molecules diffuse (move) easily in the air.

Question 10.
What is crystallisation?
Answer:
The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called
crystallisation.

Question 11.
Define chemical reaction.
Answer:
The process in which the originally present substances change into new substances is called a chemical reaction.

Question 12.
What is matter?
Answer:
Anything which occupies space and has weight is called matter. Example: Air, Water, Wood, Stone, etc.

Question 13.
What are solids?
Answer:
Any materials which has a definite shape and definite volume, at room temperature is called solid.

Question 14.
What are liquids?
Answer:
Any substance which has a definite volume but no definite shape and has one free surface is called liquids: Milk, Water, Fruit juice, Alcohol etc.

Question 15.
Name two elements that are abundantly found in air.
Answer:
The two elements that are found abundantly in air are Nitrogen element and Oxygen element.

Question 16.
Choose the elements from the following substances: Marble, Mercury, Air, Carbon.
Answer:
Mercury and Carbon are elements.

Question 17.
What is the difference between 2N and N?
Answer:
2N represent 2 atoms of nitrogen and N represent 1 molecule of nitrogen.

Question 18.
Which of the following contains only one kind of atoms?
Copper, Iron sulphide, Sulphur, Oxygen gas, Water, Air and Hydrogen gas.
Answer:
Copper, Iron, Sulphur, Oxygen gas, Hydrogen gas.

Question 19.
Which of the following substances are compounds and which are elements?
Magnesium oxide, nitrogen, potassium permanganate, sodium carbonate.
Answer:
Compounds: Magnesium oxide, Potassium permanganate, Sodium carbonate.
Elements: Nitrogen.

Question 20.
Write down the chemical symbols of the following elements: Potassium, Calcium, Phosphorus, Nitrogen, Sulphur.
Answer:
K, Ca, P₄, N and Sg.

Question 21.
Write the names of the elements having the following symbols: C, Br, P, Al, Si.
Answer:
Carbon, Bromine, Phosphorus, Aluminium and Silicon.

Question 22.
A given substance ‘X’ has definite shape, fixed volume, is in comprissible and non-diffusing. What is the physical state of the substance ‘X’?
Answer:
The substance ‘X’ is solid state.

Question 23.
Write the names of the elements which compose a molecule of water.
Answer:
Hydrogen and Oxygen.

Question 24.
Name the three most abundant elements on the earth’s crust.
Answer:
Iron, Aluminium and Silicon.

Question 25.
Give the chemical formulae of the following:
(i) Calcium hydroxide
(ii) Copper oxide
(iii) Iron chloride
(iv) Zinc nitrate
(v) Silver sulphate
(vi) Lead carbonate
(vii) Potassium phosphate
(viii) Sodium hydroxide
(ix) Hydrochloric acid
(x) Zince hydroxide.
Answer:
(i) Ca(OH)₂
(ii) CuO
(iii) FeCl₂
(iv) Zn (NO₃)₂
(v) Ag₂SO₄
(vi) PbCO₃
(vii) K₃PO₄
(viii) NaOH
(ix) HCl
(x) Zn(OH)₂.

Question 26.
Define reactents.
Answer:
The original substances that take part in a chemical reaction are called the reactants,

Question 27.
Define products.
Answer:
The substances that form as a result of chemical reaction are called the products.

Question 28.
Define chemical combination reaction.
Answer:
When two or more elements or compounds react chemically to form only one new product, then the reaction which takes place is called chemical combination.

Question 30.
Define chemical displacement reaction.
Answer:
When a more reactive element displaces a less reactive elements from its aqueous salt solution, the reaction which takes place is called chemical displacement.

Question 31.
What kind of chemical reaction takes place when a mixture of iron fillings are heated with sulphur?
Answer:
Chemical combination reaction.

Short Answer Type Questions

Question 1.
Formation of clouds is a physical change. Explain.
Answer:
Formation of clouds is a physical change. Clouds are formed by condensation of water vapours present in the atmosphere. When rainwater goes back on the earth no new product is formed. Therefore, it is a physical change.

Question 2.
Explosion of a cracker is a chemical change. Explain.
Answer:
When we burn a cracker, it exploide. Heat, light and smoke comes out after explosion. Many new products are formed. So, it is a chemical change.

Question 3.
Most physical changes are reversible. Give reasons with two examples.
Answer:
All physical changes are reversible. Because in physical changes, no new product is formed. They can be reversed easily.
Examples:
(i) Dissolving of sugar in water is a physical change and we get back sugar and water easily.
(ii) Formation of ice from water. In melting of ice, we can get water back.

Question 4.
Identify the type of change and state whether energy is evolved or absorbed in each one of the following:
Burning of a candle, lighting of a bulb, preparation of food by green plants, Volcanic eruption.
Answer:
(i) Burning of a candle: Chemical change, energy evolved.
(ii) Lighting of a bulb: Physical change, energy evolved.
(iii) Preparation of food by green plants: Chemical change, energy absorbed.
(iv) Volcanic eruption: Chemical change, energy evolved.

Question 5.
What is a chemical formula? What information does it provide?
Answer:
Chemical formula is a shorthand method of using symbols to represent the composition of a compound. Using it, we can get the following informations:
(i) Constituting name of the elements present in the compound, e.g., water has the formula H₂0. It shows that water is made up .. of two elements, hydrogen and oxygen.
(ii) Atoms present in each element, e.g.,
(iii) The composition of compound and the formula H₂O shows that in a molecule of molecular weight of the compound, this compound two atoms of hydrogen and one atom of oxygen are present.

Question 6.
What are the differences between chemical and physical changes?
Answer:
Differences between chemical and physical changes:

Question 7.
How is common salt obtained from sea water?
Answer:
In the coastal regions of India, especially in the Rann of Kutch in Gujarat and some parts of Tamil Nadu, the sea water is collected in shallow pits. It is then allowed to evaporate in the sun. As the water evaporates, the salt solution becomes supersaturated. This supersaturated solution cannot hold the excess salt. Thus, it separates out in form of salt crystals. These salt crystals are collected. They are redissolved in water and the solution is filtered to remove insoluble impurities. The clear solution is again evaporated so as to obtain the crystals of pure salt.

Question 8.
What is crystallisation? To what purpose is it put?
Answer:
The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called Crystallisation.

The process of crystallisation is employed for the separation of a pure water soluble substance from its mixture. For example, if there is a mixture of alum and common salt, the pure alum crystals can be separated by the process of crystallisation.

Question 9.
What is the significance of an equation?
Answer:
Significance of an equation:
(i) It tells us which substance reacted and which substances are produced.
(ii) It tells us the quantities of each of the reactants and each of the products.

Question 10.
Give four examples of a physical change.
Answer:
(i) Formation of dew.
(ii) Evaporation of water.
(iii) Melting of wax.
(iv) Making of ice-cream.

Question 11.
Give four examples of a chemical change.
Answer:
(i) Photosynthesis by plants.
(ii) Clotting of blood.
(iii) Curdling of milk.
(iv) Burning of candle.

Question 12.
State four characteristics of physical change.
Answer:
(i) It is temporary.
(ii) It is reversible.
(iii) No new substance is produced.
(iv) No change in the chemical properties.

Question 13.
State four characteristics of chemical change.
Answer:
(i) It is permanent.
(ii) It is irreversible.
(iii) New substance is produced.
(iv) Changes in the chemical properties due to the formation of new substances.

Question 14.
What happens when an iron blade of a knife is dipped in copper sulphate solution? What kind of chemical reaction takes place?
Answer:
When an iron blade of a knife is dipped in copper sulphate solution iron blade is coated with reddish deposit of copper. Thus, we can say that iron (more reactive element), displaces copper (less reactive element), from its aqueous copper sulphate solution. Chemical displacement reaction is takes place.

Question 15.
Why do the molecules in a liquid tend to stay together and give a condensed form?
Answer:
In a liquid, the molecular motion are not great enough to over come the force of attraction between molecules. That is why the molecules tend to stay together and give a condensed form.

Question 16.
On a hot summer day the cycle tubes burst suddenly. Explain why?
Answer:
The cycle tubes are filled with air. On a hot summer day, the temperature of the atmosphere is high. When cycle runs on the road, the friction between the cycle wheel and the path produces heat which raises the temperature of the air in the cycle tubes. On heating the air expands and exerts pressure in the inside of the tubes. Due to the pressure, the cycle burst suddenly on a hot summer day.

Question 17.
Why can the same substance exist in all the three states, that is, solid liquid and gas?
Answer:
The space between the molecules, the force of attraction between the molecules, and the amount of movement of the molecules of a substance can be changed by changing the pressure and temperature of the substance. So depending on the pressure and temperature, the same substance can exist in all the three states i.e., Solid, liquid and gaseous. For example under normal pressure water exists as a solid in the form of ice at a temperature of 0°C or below. It exists as a liquid in the form of water at the room temperature and as a gas in the form of steam at 100°C or above.

Question 18.
Write some important properties of an element.
Answer:
Properties of an element are:
(i) An element is made up of some kinds of atoms.
(ii) An element cannot be Broken up into much simpler substances,
(iii) An element can be represented by a chemical symbol.

Question 19.
What are the important characteristics of a compound?
Answer:
(i) Chemical compound is made up of two or more elements combined chemically.
(ii) They have fixed formula or composition.
(iii) They have fixed melting point (M.P.) and boiling point (B.P.).
(iv) Energy is either evolved or absorbed during formation of a compound.
(v) Properties of constituent elements are different from its compound, e.g., properties of water (H₂O) are different from properties of hydrogen and oxygen.

Question 20.
What does the formula CO₂ represent?
Answer:
Molecular formula CO₂ represents:
(i) the name of the compound carbon dioxide.
(ii) carbon dioxide is made up of two kinds of elements – carbon and oxygen.
(iii) one molecule of carbon dioxide has one atom of carbon and 2 atoms of oxygen.
(iv) the molecular mass of carbon dioxide is 12 + 2 x 16 = 44 gram.

Question 21.
How is salt obtained from sea-water?
Answer:
The seas are great sources of salts. A litre of a water contains about 35 grams of salts. Sodium chloride is the main salt. The sea-water is trapped in shallow called lagoons and is allowed to evaporate in sunlight to white solid crystal of salts. These crystals are processed and packed to send the markets.

Question 22.
Give three reasons for supporting that water is a compound and not a mixture.
Answer:
Water is considered a compound due to the following reasons:
(i) Water cannot be separated into its constituents, hydrogen and oxygen, by the physical process.
(ii) The properties of water are entirely different from those of its constituents hydrogen and oxygen.
(iii) Water contains hydrogen and oxygen combined together in a fixed proportions of 1:8 by weight.

Question 23.
Explain why solution of salt in water is considered a mixture and not a compound. Give three reasons.
Answer:
Salt solution is considered a mixture due to the following reasons:
(i) Salt solution can be separated into salt and water by the physical process.
(ii) Salt solution, shows the properties of both its constituents salt as well as water.
(iii) The composition of salt solution is variable i.e., the percentage of salt and water in different salt solutions are different.

Question 24.
What information do we get from a chemical equation?
Answer:
The informations obtained from a chemical equation are:
(i) Name of the substance (elements or compound) taking part in reaction, i.e., reactants and products.
(ii) The number of atoms and molecules of different substances.
(iii) The conditions under which the reaction takes place or taking part in reaction, for example:
N₂ + 3H₂ → 2NH₃
It represents 1 molecule of nitrogen combines with 3 molecules of hydrogen to form 2 molecules of ammonia.

Question 25.
“In a chemical reaction, there is only a rearrangement of the atoms of the reactants.” Explain this statement giving an example.
Answer:
In a chemical reaction, there is only a x’e. angement of the atoms of the reactants because when a chemical reaction occurs new products are formed. These products have same kind and number of atoms as are present in reactants. They are only rearrange to give new substances. For example, in a reaction between iron and sulphur to give iron sulphide the number of atoms of iron and sulphur are identical on both sides of the equation.
Fe + S → FeS (On heating)

Question 26.
What is done to make a chemical equation more informative?
Answer:
To make a chemical equation more informative it should be balanced and conditions of the reaction should be written above the arrow. For example,

It shows that 2 molecules of water on electrolysis break up into 2 molecules of hydrogen and 1 molecule of oxygen.

Question 27.
What do you understand by reactants and products?
Answer:
Reactants: Substances taking part in a reaction are called reactants. They are written on the left side of the chemical equation.
Products: Substances produced in a reaction are called products. They are written on the right side of the equation.
Example:

Long Answer Type Questions

Question 1.
What does a chemical formula represent?
Answer:
Significance of chemical formula:
(i) It represents the name of the substance.
(ii) It represents one molecule of the substance.
(iii) It gives the names of all the elements present in the molecule.
(iv) It represents the mass of one molecule.

As an example of the formula of H₂SO₄:
(i) Represents sulphuric acid.
(ii) Represent one molecule of sulphuric acid.
(iii) Tells that sulphuric acid contains three elements:
hydrogen, sulphur, and oxygen.
(iv) Tells that one molecule of sulphuric acid contains two atoms of hydrogen; 1 atom of sulphur and 4 atoms of oxygen.

Question 2.
What do you understand by the following terms? Give examples.
(i) Endothermic chemical change
(ii) Exothermic chemical change.
Answer:
(i) Endothermic chemical change: When a chemical change takes place with the absorption of heat energy, then the change is said to be endothermic. .
Examples: Heating of mercuric oxide to form mercury and oxygen. Heating of calcium carbonate to form calcium oxide and carbon dioxide.

(ii) Exothermic chemical change: When a chemical change takes place with the liberation of heat energy, the change is said to be exothermic.
Examples: Candle on burning liberates heat and light energy. Respiration is an exothermic change.

Question 3.
What is a compound? How does it differ from a mixture?
Answer:
A compound consists of two or more elements, joined together in a fixed ratio by chemical bonds. For example, water formed from hydrogen and oxygen, sodium chloride formed from sodium and chlorine, sugar formed from carbon, hydrogen and oxygen, nitre formed from potassium, nitrogen and oxygen are all compound.
Difference between compounds and mixtures:

Question 4.
What is the difference between a balanced and unbalanced chemical equations? Explain with an example.
Answer:
Difference between a balanced and unbalanced chemical equations:
In unbalanced chemical equations, the number of each element atoms do not same. As for example:
Mg + O₂ → MgO.
This is not a balanced equation because the number of Mg atom and oxygen atoms are not same on both the sides, Le., reactants and product sides. On the other hand, in a balanced chemical equation the number of each atoms of each elements on both sides should be equal. As for example:
2Mg + O₂ → 2MgO.
In this balanced chemical equation the number of magnesium atoms and oxygen atoms in the left hand side are equal to the right hand side of the equation. So it is a balanced chemical equations.
(i) A mixture consists of two or more chemically different substances.
(ii) The composition of mixture can be separated easily by simple means.
(iii) Its formation is not accompanied by absorption or evolution of heat, light or electricity.
(iv) Mixture do not have definite formula.
(v) Mixture do not have fixed M.P. and B.P.
(vi) Mixture can be homogeneous and heterogenous.

Question 5.
Balance the following equations:
(i) Fe + O₂ → Fe₂O₃
(ii) H₂O + H₂ → O₂
(iii) Mg + O₂ → MgO
(iv) Al + O₂ → Al₂O₃
(v) Fe + HCl → FeCl₃ + H₂
(vi) Cu + O₂ → CuO
(vii) Hg + O₂ → HgO
(viii) Zn + HCl → ZnCl₂ + H₂
(xi) Al + HCl → AlCl₃ + H₂
(x) N₂ + H₂ → NH₃
Answer:
(i) 4Fe + 3O₂ → 2Fe₂O₃
(ii) 2H₂O → 2H₂ + O₂
(iii) 2Mg + O₂ → 2MgO
(iv) 4Al + 3O₂ → 2Al₂O₃
(v) 2Fe + 6HCl → 2FeCl₃ + 3H₂
(vi) 2Cu + O₂ → 2CuO
(vii) 2Hg + O₂ → 2HgO
(viii) Zn + 2HCl → ZnCl₂ + H₂
(xi) 2Al + 6HCl → 2AlCl₃ + 3H₂
(x) N₂ + 3H₂ → 2NH₃

Physical and Chemical Changes Class 7  HBSE Notes

1. Properties such as shape, size, colour and state of a substance are called its physical properties.
2. A change in which a substance undergoes a change in its physical properties is called a physical change. A physical change generally reversible.
3. A change in which one or more new substances are formed is called a chemical change. A chemical change is also called a chemical reaction.
Some common examples of chemical change:
1. Burning of wood or charcoal.
2. Burning of Candle.
3. Decomposition of water into hydrogen and oxygen.
4. Formation of water from hydrogen and oxygen.
5. Digestion of food.
6. Curdling of milk.
7. Formation of biogas (Crobar gas).
8. Burning of petrol or diesel.
9. Smoking of cigarette.
10. Drying of paint.
11. Rusting of iron.
12. Ripening of fruit.
13. Baking of cake.
14. Photosynthesis by plants.
15. Formation of wine.

Some Common Examples of Physical Changes:
1. Formation of dew.
2. Evaporation of water.
3. Crystallisation of sugar from its solution.
4. Ringing of an electric bell.
5. Breaking of glass pane.
6. Making of ice-cream.
7. A rock rolling down a hill.
8. Bending of glass tube by heating.
9. Melting of wax.
10. Sublimation of camphor.

4. If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting.
5. Any pure substance which cannot be broken into two or more pure substances by any chemical means is called an element.
6. The smallest unit of an element, which takes part in a chemical reaction is called an atom.
7. The smallest unit of a pure substance, which always exists independently and can retain physical and chemical properties of that substance, is called a molecule.
8. A metal is an element which is generally malleable, ductile and a good conductor of heat and electricity. About 80% of the elements are metals.
9. Non-metals are bad conductors of heat and electricity. They are neither malleable nor ductile. Non-rr Hals are generally soft.
10. When the molecule of a substance contains two or more atoms of different elements, combined together in a definite ratio, then it is said to be a molecule of a compound.
Symbols of common elements (Metals)

11. When one or more substances (elements or compounds) undergo a chemical change, with the absorption or release of energy, so as to form one or more new products, then the change taking place collectively is called chemical combination.
12. When two or more elements or compounds react chemically to form only one new product, then the reaction which takes place is called chemical combination.
13. When a single chemical compound decomposes on heating or by some other kind of energy, so as to form two or more new substances (elements or compounds), then the chemical reaction which takes place is called chemical decomposition.
14. When a more reactive element displaces a less reactive element from its aqueous salt solution, the reaction which takes place is called chemical displacement.
15. When an acid solution reacts with a base or metal carbonate, so as to form a salt, then the reaction is called neutralisation reaction.
16. The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called crystallisation.

Read More:

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Haryana State Board HBSE 7th Class Science Solutions Chapter 5 Acids, Bases and Salts Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 5 Acids, Bases and Salts

HBSE 7th Class Science Acids, Bases and Salts Textbook Questions and Answers

Question 1.
State differences between acids and bases.
Answer:

Question 2.
Ammonia is found is many household products, such as window cleaners. It turns red litmus blue, what is its nature?
Answer:
Basic.

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
Litmus solution is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper.

Question 4.
Is the distilled water acidic/basic/ neutral? How would you verify it?
Answer:
The distilled water is neutral. Put a drop of the distilled water on a strip of the red litmus paper with the help of a droper. We observe that colour of the litmus paper as not change.

The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.

Question 5.
Describe the proeess of neutralization with the help of an example.
Answer:
The process due to! which an acid completely reacts with a base to form salt and water as the only products is called neutralization.
Acid + Base → Salt + Water
Example: Hydrochloric add (HCl) + Sodium hydroxide (NaOH)
Sodium chloride (NaCl) + Water (H₂O)

Question 6.
Make “T” if the statement is true and ‘F’ if it is false.
(i) Nitric acid turn red litmus blue.
(ii) Sodium hydroxide turns blue litmus red.
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.
(iv) Indicator is a substance which shows different colours in acidic and basic solutions.
(v) Tooth decay is caused by the presence of a base.
Answer:
(i) Flase
(ii) Flase
(iii) True
(iv) True
(v) True.

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink; How will Dorji decide which drink is to be served to whom?
Answer:
Do yourself.

Question 8.
Explain why?
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamane solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.
Answer:
(a) Our stomach contains hydrochloric acid. It help us to digest food. But too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

(b) The sting of an ant contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains Zinc carbonate.

(c) The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you Identify them? You have only turmeric indicator.
Answer:
Do yourself.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The nature of the solution is neutral, because the solutions which do not change the colour of either red or blue litmus are known as neutral solution. These substances are neither acidic nor basic.

Question 11.
Consider the following statements:
(a) Acids and bases both change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?
(i) All four
(ii) a and b
(iii) b and c
(iv) only d
Answer:
(ii) a and b.

Extended Learning – Activities And Projects

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet’root. Explain how it works.
(Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beet root over the message.)
Answer:
Do yourself.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and’ basic solutions with it. Present your observations in the form of a Table.
Answer:
Do yourself.

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner.
Answer:
Do yourself.

Question 4.
Visit a doctor. Find out the medicines be prescribes to treat acidity. Ask him how acidity can be prevented.
Answer:
Do yourself.

HBSE 7th Class Science Acids, Bases and Salts Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is an acid Id
Answer:
A substance which dissolves in water to give hydrogen ions as the only positively charged ions’fs called an acid.

Question 2.
What are mineral acids? Give, three examples.
Answer:
The acids which are prepared from the minerals of the Earth are called mineral acids.
Examples: Sulphuric acid, Nitric acid, Hydrochloric acid.

Question 3.
What are organic acids? Give three examples.
Answer:
Organic acids are found in plant and animal products, for examples, oxalic acids, citric acid, acetic acid, etc.

Question 4.
A solution turns red litmus solution blue. Is the solution acidic or basic in nature?
Answer:
Basic.

Question 5.
Give two examples each of (i) Strong bases (ii) Weak bases.
Answer:
(i) Strong bases: Sodium hydroxide, potassium hydroxide.
(ii) Weak bases: Copper hydroxide, zinc hydroxide. .

Question 6.
What do you understand by the term “neutral substance?”
Answer:
The substances which do not bring about any change in the colour of common indicators are called neutral substances.

Question 7.
Name the acids present in:
(i) Vinegar
(ii) Lemon juice
Answer:
(i) Acetic acid (CH₃COOH)
(ii) Citric acid.

Question 8.
Write the names of three mineral acids.
Answer:
(i) Sulphuric acid (H₂SO₄)
(ii) Nitric acid (HNO₃) and
(iii)Hydrochloric acid (HCl) are mineral acids.

Question 9.
Which of the following are oxides?
H₂O, CO, Co, NO, CO₂ , NaOH
Answer:
Oxides: H₂O, CO, NO and CO₂.

Question 10.
From the following list select metallic oxide and non-metallic oxides: CaO, Fe₂O₃, N₂O₅, CO₂, Na₂O, SO₂.
Answer:
(i) Metallic oxide: CaO, Fe₂O₃ and Na₂O.
(ii) Non-metallic oxide: N₂O₅, CO₂ and SO₂.

Question 11.
What are indicators?
Answer:
The complex, naturally occurring substances, which change their colour on coming in contact with other substances are called indicators. Turmeric, litmus, china rose etc. are some indicators.

Question 12.
Name two neutral liquids.
Answer:
(i) Alcohol
(ii) Ether.

Question 13.
Name two neutral gases.
Answer:
(i) Hydrogen, (ii) Oxygen.

Question 14.
Name two neutral solids.
Answer:
(i) Common Salt
(ii) Sugar.

Question 15.
What do you understand by term concentrated acid?
Answer:
The acids which contain very little or no amount of water are called concentrated acids.

Question 16.
What are dilute acids?
Answer:
The acids which contain a large amount of water (or solutions of acids in water) are called dilute acids.

Question 17.
Name the kind of substance formed when an acid reacts with a base.
Answer:
Neutralised.

Question 18.
What is missing in the following equation?
Fat + ……. → Soap + Glycerol
Answer:
Fat + NaOH → Soap + Glyceral
Thus NaOH missing from the equation.

Question 19.
An element combines with oxygen to form an oxide. This oxide dissolves in water. This aqueous solution changes blue litmus to red. Write:
(i) The nature of element (metal or non-metal)
(ii) The general name of the oxide.
Answer:
(i) The element is non-metal.
(ii) General name of the oxide non-metallic oxide.

Question 20.
What happens when a non-metal oxide is dissolved in water?
Answer:
When a non-metal oxide is dissolved in water, it forms acids. Examples:
(i) CO₂ + HO₂ → H₂CO₃ (Carbonic acid).
(ii) SO₂ + HO₂ → H₂SO₃(Sulphuric acid).

Question 21.
State one characteristics, property of all acids.
Answer:
All acids contain replaceable hydrogen.

Question 22.
Name the gas obtained when a metal carbonate reacts with an acid.
Answer:
When a metal carbonate reacts with an acid, carbon dioxide gas is envolved. Example:

Question 23.
Write equations for the action of water on:
(i) MgO
(ii) Calcium oxide.
Answer:
(i) MgO + H₂O → Mg(OH)₂ (Magnesium hydroxide)
(ii) CaO + H₂O → Ca(OH)₂(Calcium hydroxide)

Question 24.
What are mineral acids? Give two examples.
Answer:
Mineral acids are those acids which are obtained from the earth. Examples, Sulphuric acid, Nitric acid.

Question 25.
Name the three salts which are commonly lised at home..
Answer:
Three, salts commonly used at home are:
(i) Sodium chloride
(ii)Sodium carbonate
(iii) Sodium hydrogen carbonate.

Question 26.
Give the chemical formula of slaked lime
Answer:
Chemical formula of slaked lime is Ca(OH)₂

Question 27.
Name one/compound of calcium which is used for bleaching cloth.
Answer:
Bleaching powder.

Question 28.
What is the formula of sulphuric acid?
Answer:
The formula of sulphuric acid is H₂SO₄.

Question 29.
A solution turns red litmus paper blue. What does this indicate about the chemical nature of the solution?
Answer:
The chemical nature of the solution is acidic.

Question 30.
What do you understand by anhydrous salt?
Answer:
Hydrated salts loose their water of crystallisation upon heating. They love their shape and colour also and becomes powered. They are called anhydrous salts.

Question 31.
Name two normal salts.
Answer:
(i) Sodium Chloride (NaCl)
(ii) Potassium nitrate (KNO₃).

Question 32.
Name two basic sdlts.
Answer:
(i) Calcium hydrdgen chloride [Ca(OH)Cl]
(ii) Magnesium hydroxy chloride [Mg(OH)Cl] etc.

Question 33.
Write the balanced chemical equations for the reaction that takes place when zinc, magnesium and sodium react with dilute hydrochloric acid.
Answer:
Reaction of hydrochloric acid (dil.) with Zn, Mg, and Na:
(i) Zn + 2HCl → ZnCl₂ + H₂
(ii) Mg + 2HCl → MgCl₂ + H₂
(iii) 2Na + 2HCl → 2NaCl + H₂

Question 34.
Write two uses of slaked lime.
Answer:
Uses of slaked lime:
(i) It is used in manufacture of bleaching powder.
(ii) It is used as an important building materials

Question 35.
Complete the following equations:
(i) CO₂ + H₂O → ……………..
(ii) CO₂ + 2Na0H → …………….. + ……………..
(iii) SO₂ + H₂O → ……………..
(iv) MgO + H₂SO₄ → …………….. + ……………..
(v) CaC0₃ + 2HCl → …………….. + ……………..
(vi) Na₂O + H₂O → ……………..
(vii) 2NaOH + H₂SO₄ → …………….. + ……………..
(viii) NaOH + HNO₃ → …………….. + ……………..
(ix) CaO + H₂SO₄ → …………….. + ……………..
(x) MgO + 2HCl → ……………..
Answer:
(i) CO₂ + H₂O → H₂CO₃ (carbonic acid)
(ii) CO₂ + 2Na0H → Na₂CO₃ + H₂O (sodium carbonate)
(iii) SO₂ + H₂O → H₂SO₃ (suiphurous acid)
(iv) MgO + H₂SO₄ → MgSO₄ + H₂O (magnesium sulphate)
(v) CaC0₃ + 2HCl → CaCl₂ + H₂O + CO₂ (Calcium Chloride)
(vi) Na₂O + H₂O → 2Na0H (sodium hydroxide)
(vii) 2NaOH + H₂SO₄ → Na₂SO₄ + H₂O (sodium suphate)
(viii) NaOH + HNO₃ → NaNO₃ + H₂O (sodiùm nitrate)
(ix) CaO + H₂SO₄ → CaSO₄ + H₂O (calcium sulphate)
(x) MgO + 2HCl → MgCl₂ +H₂O

Short Answer Type Questions

Question 1.
How can you test the presence of an acid in any substance?
Answer:
Acid can be tested in any substance by the following methods:
(i) Take a drop of the dilute solution of the substance on the tips of your tongue. If tastes sour, it is acidic.
(ii) Dip a blue litmus paper in the solution. If ‘ the colour of the litmus paper turns red, the solution is acidic.

Question 2.
What are organic acids? Give two examples.
Answer:
Soured milk, Lemon, Green mangoes and Karvanda are sour testing. All of them contain some naturally occuring acids. Such acids are also found in humans and plants materials. They are known as organic acids. The acids such as lactic acid, citric acid, tartaric acid and acetic acid are naturally occuring and known as organic acid.

Question 3.
What are the uses of mineral acids in industry?
Answer:
Use of’mineral acids in industry:
(i) Concentration sulphuric acid, nitric acid and hydrochloric acid are used in a large number of metallurgical operations, manufacture of fertilizers and preparations of large number of industrial chemicals.
(ii) Hydrochloric acid is used for removing the deposits from inside the boilers. This process is known as de-scaling.

Question 4.
What are indicators? Name two acid-base indicators.
Answer:
The substances which are used to identify whether a substance is an acid or base is called indicators. For example, litmus solutions give red colour with acids and blue colour with bases. Therefore, litmus is used as indicators. Substances which give different colours with acid and base are called acid-base indicators, for examples. Methyl orange, phenolphthalein.

Question 5.
What are acid salts? Give two examples.
Answer:
The salts which dissolves water to produce a solution, which behaves like an acid is called an acid salt.
Examples: Sodium hydrogen carbonate (NaHCO₃), Potassium hydorgen carbonate (KHCO₃), Sodium hydrogen sulphate etc.

Question 6.
How is potash alum prepared?
Answer:
A mixture of potassium sulphate and aluminium sulphate is dissolved in water and then the solution is concentrated. Potash alum is formed. It separates out as crystals.

Question 7.
Why are sodium bicarbonate and lemon juice used during indigestion?
Answer:
Sodium bicarbonate neutralizes the acidity in the stomach. Hence, it is used during indigestion. Lemon contains acid. It reacts with undigested food and softens it. Thus, lemon is also used in indigestion.

Question 8.
Why are brass vessels coated with tin or kalai?
Answer:
When brass vessels are used to cook food with tamarind or lemon juice, the acids present in it reacts with brass metal and corrode it. The kalai layer protects this vessels from the action of acids. Due to this reason brass vessels are coated with tin.

Question 9.
What is salt? Name any salts and give thier formulae.
Answer:
A substance formed by the neutralisation of an acid with a base is called salt.
Examples:
(i) Potassium nitrate (KNO₃)
(ii) Sodiun: nitrate (NaNO₃)
(iii) Calcium carbonate (CaCO₃)
(iv) Zinc sulphate (ZnSO₄)
(v) Copper sulphate (CuSO₄).

Question 10.
Define an acid. Give three properties of acids.
Answer:
An acid is a substance which when dissolved in water gives hydrogen ions. Examples: H₂SO₄, HNO₃ and HCl etc.
Properties of acids:
(i) They have a sour taste
(ii) They turn blue litmus solution red.
(iii) They have replaceable hydrogen ion.

Question 11.
What are bases? Mention three properties of alkalies.
Answer:
The substance which react with acids to form salt and water only are called bases. Examples: Cu(OH)₂, Fe(OH)₃, Pb(OH)₂ etc.
Properties of alkalies:
(i) They tarn red litmus paper blue
(ii) They have a better taste.
(iii) They turn methyl orange from pink to yellow.

Question 12.
What are the uses of sodium bicarbonate?
Answer:
Uses of sodium bicarbonate:
(i) It is used in medicines to neutralise the acidity in the stomach.
(ii) It is used as backing power.
(iii) It is used in fire extinguisher.

Question 13.
What are the uses of common salt?
Answer:
Uses of common salt:
(i) It is an essential constituents of our diet.
(ii) It is used in the manufacture of soap.
(iii) It is used for glazing pottery. .
(iv) It is a starting material for the manufacture of chlorine, hydrochloric acid, washing soda and sodium hydroxide.
(v) It is used as food preservatives.
(vi) It turns freezing mixture with ice.

Question 14.
Give five uses of potassium nitrate.
Answer:
Uses of potassium nitrate:
(i) It is used in the manufacture of gun powder.
(ii) It is used in making fire works.
(iii) It is used in refrigeration.
(iv) It is used as fertilizers.
(v) It is used in glass industry.

Question 15.
Which acids is called ‘the king of the acids’? Give its uses.
Answer:
Sulphuric acid (H₂SO₄) is called “the king of the acids”.
Uses of sulphuric acid:
(i) It is used in the manufacture of detergents.
(ii) It is used as a dehydrating agent.
(iii) It is used in storage batteries.
(iv) It is used in petrol refining.
(v) It is used in textile, paper and leather industry.
(vi) It is used in fertilizers industry for the manufacture of ammonium sulphate and superphosphate of lime.

Question 16.
Explain with the help of chemical equations how the following acids are formed?
Carbonic acids, Sulphurous acid, Phosphoric acid.
Answer:
(i) Carbonic acid is prepared by dissolving carbon dioxide in water.
CO₂ + H₂O → H₂CO₃ (Carbonic acid)

(ii) Sulphurous acid is formed by dissolving sulphur dioxide in water.
SO₂ + H₂O → H₂SO₃ (Sulphurous acid)

(iii) Phosphoric acid is prepared by dissolving phosphorus pentaoxide in hot water.
P₂O₅ + 3H20 → 2H₃PO₄ (Phosphoric acid)

Acids, Bases and Salts Class 7 HBSE Notes

1. Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids. The chemical nature of such substances is acidic. The word acid comes from the Latin word acere which means sour. The acids in these substances are natural acids.
2. A substance which produces hydrogen (H⁺) ions when dissolved in water is called an acid. This definition was given by Arrhenius, a Swedish Chemist in 1912.
3. The acids which are prepared from the minerals of the Earth are called mineral acids.
Examples of Mineral Acids

4. The acids which dissolve in water to give a large number of positively charged hydrogen ions are called strong acids.
Examples of Strong Acids : Sulphuric acid, nitric acid, hydrochloric acid and phosphoric acid are examples of strong acids.
5. The acids which dissolve in water to give a small number of positively charged hydrogen ions are called weak acids.
Examples of Weak Acids : Carbonic acid, acetic acid, sulphurous acid, formic acid, etc., are examples of weak acids. In fact, most of the organic acid are weak acids.
6. The acids which contain very little or no amount of water are called concentrated acids.
7. The acids which contain a large amount of water (or solutions of acids in water) are called dilute acids.
8. General Physical Properties of Acids
(i) They have a sour taste.
(ii) They turn blue litmus solution red.
(iii) They turn methyl orange solution pink.
(iv) They do not affect phenolphthalein solution.
(v) Strong acids have a corrosive action on skin. They cause painful blisters.
(vi) Most of the acids are soluble in water.
(vii) Acids solutions are conductors of electricity.
9. Uses of Acids

10. The substances which react with acids to form salt and water as only products are called bases. All oxides of metals are bases. All hydroxides of metals are bases.
11. All bases which are soluble in water are called alkalis.
12. Strong bases completely dissociate in aqueous solution. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), etc.
13. They undergo partial dissociation in aqueous solution. For example, copper hydroxide Cu(OH)₂, Zinc hydroxide Zn(OH)₂, etc.
14. The bases show the following properties:
(i) These have a bitter taste.
(ii) Bases neither have colour nor small. Only Ammonium hydroxide (NH₄OH) has a pungent smell.
(iii) The basic solutions are soapy to touch, i.e., if little amount of sodium hydroxide is rubbed on fingers, it would give a feeling as if soap has been applied on the fingers.
(iv) Bases turn red litmus blue.
(v) Bases contain hydroxide ions e.g., Sodium hydroxide is represented as NaOH, calcium hydroxide is represented as Ca(OH)₂, etc., where OH is the hydroxy group.
(vi) Bases react with acids to give salt and water.
15. Uses of Bases

16. Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. Turmeric, litmus, china, rose, petals (Gudhal), etc., are some of the naturally occurring indicators.
17. The reaction between an acid and a’base-is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water (Heat is evolved)
The following reaction is an example :
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O)

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Haryana State Board HBSE 7th Class Science Solutions Chapter 9 Soil Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 9 Soil

HBSE 7th Class Science Soil Textbook Questions and Answers

Tick the most suitable answer in questions 1 and 2.

Question 1.
In addition to the rock particles, the soil contains:
(i) air and water,
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants.
Answer:
(iii) minerals, organic matter, air and water.

Question 2.
The water holding capacity is the highest in:
(i) sandy soil
(ii) clayey soil
(iii) loamy soil
(iv) mixture of sand and loam
Answer:
(iii) loamy soil.

Question 3.
Match the items in column I with those in column II:

Answer:

Question 4.
Explain how soil is formed.
Answer:
Soil has been formed from parent rock material over millions of years. The process by which soil formation takes place is called weathering. Weathering is a very slow and gradual process during which parent rock material breaks down into fine particles.

The agents which bring about weathering are many. These are described below:
1. Temperature changes:
Rocks expand when heated and contract when cooled. The hot sun causes the surface layers of rocks to expand more than the layers deeper down. These changes cause the rock surface to break apart.

2. Frost:
Rainwater may become trapped in small crevices of the parent rock. In winter, this water freezes to ice. The ice expands producing a lateral pressure, causing the crevices in the rocks to further open up.

3. Water:
Continual movement of rain and river water, in liquid form, causes breaking down of rock particles into finer particles through their abrasive effect.

4. Wind:
Wind blowing across a rock surface also has a abrasive effect on the rocks. Minute rock particles are carried away by the blowing wind and deposited elsewhere.

Question 5.
How is clayey soil useful for crops?
Answer:
Clayey soils are very useful for crops, because these soils:
(i) contain humus, providing fertility to the soil
(ii) hold sufficient water due to the presence of smaller particles, and
(iii) contain enough air due to the presence of some large particles alsy.

Question 6.
List the differences between clayey soil and sandy soil.
Answer:
Clayey soil:
Clayey soil contains more than 50% of clay particles. Since the clay particles are very small in size, they are very tightly packed and do not allow water to drain out easily. It is poorly aerated because the tightly bound clay particles leave little space in between to trap air. Clayey soil is very sticky and thus tilling the soil is very difficult. However, it is rich in minerals which makes it suitable for plant growth. Due to the great binding capacity of its particles, clayey soil is used for making toys and pots.

Sandy soil:
Sandy soil contains about 60% of sand particles with small amounts of silt and clay. It is very porous and its water holding capacity is very low as all the water easily runs down through the large pores. This type of soil is, therefore, not good for the growth of plants. It is found mainly in the deserts.

Question 7.
Sketch the cross section of soil and label the various layers.
Answer:
Soil profile

Question 8.
Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Answer:
Formula: Percolation rate
\((\mathrm{mL} / \mathrm{min})=\frac{\text { amount of water }}{\text { percolation time }(\mathrm{min})}\)
= \(\frac{200 \mathrm{~mL}}{40 \mathrm{~min}}\)
= 5 mL /min.

Question 9.
Explain how soil erosion could be prevented.
Answer:
Prevention of soil erosion can be brought about by controlling the factors which cause soil erosion. The methods would, thus, be as follows:
1. Deforestation should be stopped. Rather, trees should be planted (afforestation). Afforestation should be undertaken not only in areas already cut, but additional areas should be brought under plantation.

2. To reduce the effect of strong winds in the fields, the boundaries of the fields should be planted with trees in two to three rows.

3. To maintain the soil in its natural condition, it is advisable to grow different crops. Crops rotation, as it is called, helps to maintain the fertility of the soil. The water-holding capacity of the soil is also maintained by this method.

4. Proper drainage and irrigation arrangements should be made in the fields.

5. On the sloping areas in hills, strip cropping should be practised, thereby reducing the steepness of the slopes and checking soil erosion.

Question 10.
Solve the following crossword puzzle with the clues given:

Across:
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.

Down:
1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.
Answer:

Extended Learning – Activities And Projects

Question 1.
Boojho would like to know the difference between raw and baked soil? Investigate how the soil from which matkas are made is different from the soil used to make status.
Answer:
Do yourself. Take help your teacher.

Question 2.
Paheli is worried. She could see a brick kiln from her house. Bricks were being made there. There was so much smoke coming out of the kiln. She was told that the best quality of clay is required for making pottery, statues and bricks. She has seen truck loads of bricks being taken away for construction of buildings. At this rate, she fears, no soil will be left. Are her fears justified? Discuss this problem with your parents, teachers and other experts of your area and prepare a report.
Answer:
Do yourself.

Question 3.
Try to find out the moisture content of a soil sample. One method is given here.
Activity: Take lOOg soil. (Take help from any shopkeepers to weigh the soil). Place it on a newspaper in the sun and allow it to dry for two hours. This activity is best done in the afternoon. Take care that the soil does not spill outside the newspaper. After drying it, weigh the soil again. The difference in the weight of the soil before and after drying gives you the amount of moisture contained in 100 g of soil. This is called the percentage moisture content.
Suppose your sample of soil loses 10 g on drying. Then
Percent of moisture in soil
= \(\frac{\text { wt. of moisture }(\mathrm{g})}{\text { Original wt. of soil sample }(\mathrm{g})} \times 100\)
In this example
Percent of moisture in soil
= \(\frac{10 \times 100}{100}=10 \%\)
Answer:
Do yourself.

HBSE 7th Class Science Soil Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define soil.
Answer:
Soil is uppermost layer of earth’s crust, in which plants grow.

Question 2.
Define weathering.
Answer:
Soil is formed from the parent rock material by a very slow and gradual process called weathering.

Question 3.
What is humus?
Answer:The rotting dead matter in the soil is called humus.

Question 4.
Where do plants grow?
Answer:
Plants grow in the soil.

Question 5.
Where does food that helps to sustain and grow, come from?
Answer:
Plants.

Question 6.
How old is our earth?
Answer:
Our earth came into existence about 4.5 billion years ago.

Question 7.
Name the part of the environment which supports life.
Answer:
1. Lithosphire
2. Hydrosphere
3. Atmosphere.

Question 8.
Give one term for the following,
“Removal of top soil by air and water.”
Answer:
Soil erosion,

Question 9.
What do you understand by the term soil conservation?
Answer:
Prevention of soil erosion is called soil conservation.

Question 10.
What is soil pollution?
Answer:
When the structure and properties of the soil are changed by adding unwanted and harmful substances, it is called as soil pollution.

Question 11.
Name two soil pollutions.
Answer:
(i) Insecticides and herbicides
(ii) Industrial wastes like plastic, chemicals, flyash, leather etc.

Question 12.
How soil erosion takes place?
Answer:
When the over grazing or cutting of trees take place the top soil becomes soft and loose which is easily blown by wind and water.

Question 13.
How is soil formed?
Answer:
Soil is formed by cracking of rocks due to contraction and expansion by cooling and heating effect.

Question 14.
What is mineral?
Answer:
Minerals are the non-renewable natural resources.

Question 15.
Name four animals that live in the soil.
Answer:
Bacteria, Earthworm, Snakes, Rats, Ants.

Question 16.
What do you understand by deforestation?
Answer:
When the trees of the forest are cleared to convert the forest land into formland is called deforestation.

Question 17.
State two major problems caused by excessive deforestation.
Answer:
(i) Due to excessive deforestation there is less rain.
(ii) Soil erosion takes place.

Question 18.
Name the materials present in fertile soil.
Answer:
Fertile soil contains nitrates, phosphates, water soluble salts and carbonic acids.

Question 19.
What is crumb?
Answer:
The main skeleton of a fertile soil is called crumb.

Question 20.
What, is the function of air in soil?
Answer:
(i) Air helps, 1:he plants present in the soil in respiration.
(ii) It helps in making soil soft and light in weight.

Question 21.
Which soil horizon is rich in humus?
Answer:
The uppermost layer is called the A- horizon is rich in humus.

Question 22.
Which type of soil is best suited for growth of plants?
Answer:
Loamy soil.

Question 23.
Name the different types of particles present in soil.
Answer:
Soil consists of soil particles, humus (organic matter), water, air and living organisms.

Question 24.
What is strip, cropping?
Answer:
Strip cropping means the planting of crops in rows or strips to check flow of water.

Question 25.
What are loams?
Answer:
Soils having mixtures of different sized particles are called loams or loam soils.

Short Answer Type Questions

Question 1.
What are the components of soil?
Answer:
Some of the main components of soil are as follows:
(i) Humus
(ii) Minerals
(iii) Water
(iv) Air and
(v) Micro organisms 7 bacteria, fungi, insects, larvae and many other organisms.

Question 2.
Write the importance of Humus.
Answer:
Humus is very important for the proper growth of the plants. It helps in growing plants in the following ways:
(i) It makes the soil fertile.
(ii) It allows the roots of plants to penetrate in the soil easily.
(iii) Water and air can pass into it easily,
(iv) It retains water for a longer period.
(v) It binds the soil particles.

Question 3.
What is meant by term wehtherifig?
Answer:
The cooling and heating of rocks cause cracking. They bring about further breaking. This process of breaking the parent rock into fine particles is called weathering.

Question 4.
Describe the harmful effects of deforestation.
Answer:
Deforestation causes the following harmful effects:
(i) Soil erosion will take place.
(ii) There will be draught due to which famine will occur. .
(iii) There will be less rain.
(iv) There will be excess amount of CO, due to which Green House effect will take place. It may cause flood in-the rivers.

Question 5.
Why biosphere supports life?
Answer:
Biosphere has all those requirements such as air, water, minerals, sunlight etc. which are essential for the survival of living things.

Question 6.
What are natural resources?
Answer:
Natural resources are those which are provided by nature to support life. Such as water, air, minerals, sunlight and various life forms.

Question 7.
What is soil erosion?
Answer:
The top soil being soft and light is carried away easily by wind and water, the natural agents. This process of removal of soil is called soil erosion.

Question 8.
Distinguish between residual and transported soils.
Answer:
Residual soils are those in which the whole process of soil formation, i.e., weathering and development of soil profile occurs at the same place. In these soils, the soil is formed at the place where the parent rock is present.

Transported soils are those where the v weathered soil particles are taken away to other places. This is done by several agents.

Question 9.
State any four major advantages of forests.
Answer:
Forest is a natural renewable resource which is advantageous in the following ways:
(i) It creates a suitable environment for rain.
(ii) It helps in controlling the soil erosion.
(iii) It absorbs excess rain water as subsoil water.
(iv) It provides the home to variety of animals.

Question 10.
What is the importance of soil organisms?
Answer:
A number of organisms such as earthworms, bacteria, fungi and round- worms are found in the soil.
Soil organisms are important because of various uses:
1. As you know, earthworms burrow the soil, swallow it and make it loose and soft.
2. Micro-organisms cause the decomposition’ of dead plants and animals, and release the minerals back of the soil. The minerals can again be absorbed by the plant roots. Mineral cycling goes on in this manner.
3. Some bacteria are able to fix nitrogen in association with roots of legume plants like pea and gram.

Long Answer Type Questions

Question 1.
How is soil important to us? Explain.
Answer:
Our mother Earth is blessed with immense land resource. It is valuable to man for food production. It is also a basic part of wildlife habitats and recreational resources. Various soil organisms like earthworms, bacteria, insects and mammals use this as a natural habitat. Plants obtain water and minerals through this land resource. Plant sources of many medicinal drugs exist here. Wood fibres, fruits, rubber, oils, dyes and various other economic products which the man uses, are all dependent on this land. The very existence of mankind is greatly influenced by this land resource.

Question 2.
Describe the factors which cause soil erosion.
Answer:
Soil erosion is the removal of topsoil. This is brought about by wind and water or rain. There are several factors which allow water and wind to cause soil erosion. Some of these factors are:
(i) Deforestation:
Cutting down of trees and excessive farming are practices that destroy vegetation and expose land to the action of wind and water. Water runs off the soil surface with great speed and carries the soil particles into rivers which get chocked with silt resulting in floods. This problem assumes alarming proportions on hills.

(ii) Overgrazing:
Overgrazing by animals also destroys vegetation making land barren. The top soil on barren land can then be eroded by water and wind.

(iii) Poor methods of farming:
Tilling or ploughing loosens the soil which can then be easily eroded by wind and water. Due to excessive farming the layer of humus gets depleted and water holding capacity of the soil also reduces. The topsoil thus dries up and can be carried away by wind and water.

(iv) Forest fires, too, lead to soil erosion. After fire, the soil is exposed to two main factors causing erosion, namely wind and water.

Question 3.
Write short notes on the importance of the following:
(а) Soil, (b) Forests, (c) Soil organisms, (d) Overgrazing, (e) Earthworms.
Answer:
(a) Soil:
(i) Soil provides shelter to several micro-organism and some macro- organisms.
(ii) All the plants grow in it.
(iii) It acts as store-house of minerals.
(iv) It acts as raw material for building bricks, mortar, pottery, pulp for paper industry is. obtained from plants grown in the soil.
(v) It acts as water storage.
(vi) It provides employment.

(b) Forests: Forests are very useful to man-kind in the following ways:
(i) It maintains the balance of gases in the atmosphere.
(ii) It causes rain.
(iii) It provides the shelter to the wild animals.
(iv) It provides the valuable things like timber, honey, bee wax, lac, medicines.

(c) Soil Organisms:
Various micro organisms live in the soil which make the soil porous, soft and airy. They make soil fertile. They convfert manure into simple form which can be used by plants of the forest.

(d) Overgrazing:
When the cattle , eat grass of l^rge area, it is called as overgrazing. This process makes the soil plain which can be used for industrialisation and urbanisation.

(e) Earthworm:
Earthworms are the friends of the farmer. They eat dead organicv substances along with the soil and convert them into simple soluble forms which make the soil fertile and soft.

Question 4.
Describe the composition of soil.
Answer:
Composition of soil varies from place to place. It depends on the type of rock from which it is formed. However, all soils contain the following components:
(i) Rock particles: Tiny particles of soil derived from the parent rock.
(ii) Humus: Humus consists of decaying remains of plants and animals.
(iii) Living organisms: Soil contains a large number of micro-organisms like bacteria, algae, fungi and protozoa. Many small animals like insects, earthworms, spiders, scorpions, centipedes and millipedes are found in the soil. Burrowing animals like rats, moles, rabbits and guinea pigs make tunnels in the soil.
(iv) Water: Water is present in pores between soil particles and helps the plants in their growth.
(v) Air: Air is also present in the soil pores and is essential for the survival of living organisms present in the soil.

Question 5.
What is soil pollution? What are the major sources of soil pollution?
Answer:
Any substance that adversely affects the, productivity of soil is called a soil pollutant. Contamination of soil with pollutants like insecticides, artificial fertilizers and industrial wastes is called soil pollution. The major sources of soil pollution are:
(i) Pollutants like acids washed off from the atmosphere (acid rain).
(ii) Pesticides and herbicides sprayed in fields.
(iii) Excessive use of artificial fertilizers.
(iv) Solid wastes like garbage, trash, ash, building material, plastic bottles and cans.

Soil Class 7 HBSE Notes

1. Soil is the uppermost layer of earth’s crust, in which plants grow.
2. Soil is formed from the parent rock material by a very slow and gradual process called weathering. A number of agents temperature changes, frost, water, wind and living organisms – are involved in the weathering of rocks.
3. Six types of soil are mainly found in India – Red soil, black soil, alluvial soil, desert soil, mountain soil and laterite soil. Humus content is maximum in mountain soil. Black soils are rich for growing cotton and sugarcane while alluvial soil is suitable for wheat and rice.

4. There are three main layers or horizons in the soil profile – A-horizon (top soil), B horizon (subsoil) and C-horizon (parent rock).
5. Soil consists of soil particles, humus (organic matter), water, air and living organisms.
6. Soil particles, depending on size, consist of clay (below 0.002 mm), silt (0.002 to 0.02 mm), sand (0.02 to 2.0 mm) and gravel (above 2.0 mm).
7. A soil containing a mixture of sand, silt and clay is called a loamy soil. It is the best soil for plant growth.
8. Soil is an important natural resource. It provides us food, clothing, shelter, medicines,
rubber, dyes and a number of other useful products. Besides man, it provides shelter to wildlife and different soil organisms.
9. Wind and rain bring about loss of the top soil (soil erosion). Deforestation, over grazing and poor farming methods have accelerated the process of soil erosion.
10. Prevention of soil erosion (soil conservation) can be brought about by growing plants (afforestation), crop rotation, prevention of over grazing maintaining proper drainage, and growing of crops in rows or strips in the hills (strip-cropping).

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Haryana State Board HBSE 7th Class Science Solutions Chapter 13 Motion and Time Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 13 Motion and Time

HBSE 7th Class Science Motion and Time Textbook Questions and Answers

Question 1.
Classify the following as motion along a straight line, circular or oscillatory motion :
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry go round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bed.
(vi) Motion of a train on a straight bridge.
Answer:
(i) Oscillatory
(ii) along a straight, line
(iii) circular
(iv) oscillatory
(v) oscillatory
(vi) along a straight line.

Question 2.
Which of the following is not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distance between two cities are measured in kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.
Answer:
(ii), (iv) (v).

Question 3.
A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Answer:
Time period of a pendulum is time taken to complete 1 oscillation
Time taken to complete = 32 s.
20 oscillations
Time taken to complete = \(\frac { 32 }{ 20 }\)s.
1 oscillation
= 1.6 s.
∴ Time period of pendulum is 1.6 seconds.

Question 4.
The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Answer:
Distance = 240 km.
Time taken = 4 hr.
Speed = \(\frac { Distance covered }{time taken }\)
= \(\frac { 240 }{ 4 }\) \(\frac { km }{ h }\)
= 60 km/h.
Speed of the train is 60 km/h.

Question 5.
The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/ h also.
Answer:
Distance = 57336.0 km – 57321 km = 15 Km
Time = 8.50 Am. – 8.30 Aim. = 20 min
Speed = \(\frac { Distance }{ time }\) = \(\frac { 15 }{ 20 }\) km/m
= 0.75 km/m. = 45 km/h

Question 6.
Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s. Calculate the distance between her house and’the school.
Answer:
Time taken = 15 min
Speed = 2 m/s.
Distance = Speed x time
= 15 x 2
= 30 m.
So, distance between Salma’s School and her house is 30 metre.

Question 7.
Show the shape of the distance-time graph for the motion in the following cases :
(i) A car moving with a constant speed.
(ii) A car parked on a side road.
Answer:

Question 8.
Which of the following relations is correct?
(i) Speed = Distance x Time
(ii) Speed = \(\frac { Distance }{ Time }\)
(iii) Speed = \(\frac { Time }{ Distance }\)
(iv) Speed = \(\frac { 1 }{ Distance x Time }\)
Answer:
(ii) Speed = \(\frac { Distance }{ Time }\) is correct.

Question 9.
The basic unit of speed is :
(i) km/min
(ii) m/min
(iii) km/h
(iv) m/s
Answer:
(iv) m/s

Question 10.
A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is :
(i) 100 km
(ii) 25 km
(iii) 15 km
(iv) 10 km
Answer:
(ii) 25 km

Question 11.
Suppose, the two photographs shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs. Calculate the speed of the blue car.
Answer:
0.1 cm/s or 10 m/s.

Question 12.
Fig. 13.16 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Answer:
‘A’ car is moving faster.

Question 13.
Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Answer:

Extend Learning – Activities and Projects

Question 1.
You can make your own sundial and use it to mark the time of the day at your place. First of all find the latitude of your city with the help of an atlas. Cut out a triangular piece of a cardboard such that its one angle is equal to the latitude of your place and the angle opposite to it is a right angle. Fix this piece, called gnomon, vertically along a diameter of a circular board a shown in Fig. 13.4. One way to fix the gnomon could be to make a groove along a diameter on the circular board.

Next, select an open space, which receives sunlight for most of the day, Mark a line on the ground along the North-South direction. Place the sundial in the sun as shown in Fig. 13.4 Mark the position of the tip of the shadow of the gnomon on the circular board as early in the day as possible, say 8:00 AM. Mark the position of the tip of the shadow every hour throughout the day. Draw lines to connect each point marked by you with the centre of the base of the gnomon as shown in Fig. 13.4. Extend the lines on the circular board up to its periphery. You can use „ this sundial to read the time of the day at your place. Remember that the gnomon should always be placed in the North- South direction as shown in Fig. 13.4.

Answer:
Do it yourself.

Question 2.
Collect information about time-measuring devices that were used in the ancientitimes in different partrs of the world. Prepare a brief write up on each one of them. The write up may include the name of the device, the place of its origin, the period when it was used, the unit in which the time was measured by it and a drawing or a photograph of the device, if available.
Answer:
Do it yourself

Question 3.
Make a model of a sand clock which can measure a time interval of 2 minutes (Fig. 13.5).

Answer:
Do it yourself

Question 4.
You can perform an interesting activity when you visit a park to ride a swing. You will require a watch. Make the swing oscillate without anyone sitting on it. Find its time period in the same way as you did for the pendulum. Make sure that there are no jerks in the motion of the swing. Ask one of your friends to sit on the swing. Push it once and let it swing naturally. Again measure its time period. Repeat the activity with different persons sitting on the swing. Compare the time period of the swing measured in different cases. What conclusions do you draw from this activity?
Answer:
Do it yourself.

HBSE 7th Class Science Motion and Time Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is motion?
Answer:
Motion is the change in the position of a body with respect to time and its surroundings.

Question 2.
What is uniform motion?
Answer:
When a body covers equal distance in equal intervals of time, the motion is called uniform motion.

Question 3.
What is speed?
Answer:
Speed is the distance covered by a body in a unit time.

Question 4.
Write one way in which people used to measure time in early days?
Answer:
People used to measure time with the help of Sundials.

Question 5.
What is the use of stop-watch?
Answer:
Stop-watch is used to measure exact time in case of athletic events as it can be stopped and started any moment.

Question 6.
What is a pendulum?
Answer:
A pendulum is a small non-magnetic ball like body, suspended by a light string.

Question 7.
What is a uniform motion?
Answer:
Motion of a body along a straight line covering equal distances in equal intervals of time is called a uniform motion.

Question 8.
What are the units of measuring speed?
Answer:
Speed is measured in metre per second (m/s) or kilometre per hour (km/h).

Short Answer Type Questions

Question 1.
Distinguish between uniform and non-uniform motion.
Answer:
Uniform motion is the equal distances covered in equal intervals of time. It means body moves with a constant speed. Non-uniform motion is the unequal distances covered in equal intervals of time. It means the body moves with unconstant speed.

Question 2.
How can we make a pendulum of our own? What is the time period of a pendulum?
Answer:
We can make a pendulum by susptending a metal ball with a cotton thread. The other end of the thread can be tied to some support. The time taken by a pendulum to complete its to and fro movement i.e. one oscillation is called the time period of the pendulum.

Question 3.
How can we determine the motion made by any body to be uniform or non-uniform with the help of a distance – time graph?
Answer:
If the distance – time graph obtained shows a straight line, the motion of the body is said to be uniform and if we obtain a curved line on a distance time graph that means the body is undertaking non-uniform motion. Thus a distance time graph helps in determining the uniform or non-uniform speed of the body.

Question 4.
A train is running at a speed of 50 km/h. How long will it take to cover a distance of 250 km.?
Answer:
Speed = 50 km/h
Distance = 250 km.
Time = ?
S = \(\frac { d }{ t }\)
50 = \(\frac { 250 }{ t }\)
∴ t = \(\frac { 250 }{ 50 }\) hr = 5 hr.

Question 5.
Shatabdi Express takes 6 hours to reach Lucknow, at a speed of 60 km/h. Find the distance it travels.
Answer:
Time = 6 hr.
Speed = 60 km/h
Distance = Speed x time
= 60 x 6 = 360 km
∴ Shatabdi travels 360 km at a speed of 60 km/h in 6 hr.

Question 6.
A car travels a distance of 200 km at the speed of 50 km/h. Calculate the time taken to cover the distance.
Answer:
Distance = 200 km
Speed = 50 km/h
Time = \(\frac { Distance }{ Speed }\) = \(\frac { 200 }{ 50 }\) = 4h
Car will take 4 h to cover the distance.

Long Answer Type Questions

Question 1.
Given below is a table showing time taken by a car to travel various distances. What do you infer from this data?

Answer:
We see that the car covers the distance of first 10 m in 1 sec. It again covers the distance of 10 m in another time of 1 sec i.e. 2-1 = 1 sec. So, we find that the car covers every 10 m in each 1 sec. It means that the car is covering equal distance in equal interval of time. When a body covers equal distance in equal intervals of time, it is said to be in a uniform motion. So, this data shows that the car is moving with a constant speed.

Question 2.
Describe various methods used to measure time in earlier times?
Answer:
There were no electronic watches in earlier times. Measuring time was a little bid difficult. The earliest method of measuring time was based on the position of the Sun. The Sundials were used for this purpose. Time was measured by the shadow casted by the changing position of the Sun from day to night. Chinese made a water clock 6000 years ago. Sand Clock was also used to measure time. Sand Clock was used by Romans. The time taken by sand to fall into the lower chamber from the upper chamber was considered to be the unit of measuring time. The discovery of pendulum helped in determining the exact time before the electronic watches were invented.

Question 3.
What is a pendulum? How does it help in determing time?
Answer:
Pendulum is a simple device which shows periodic motion. A simple pendulum consists of a non-magnetic metal ball called bob. This bob is suspended with help of a string. The open end of the string is tied to a support. Bob of the pendulum is held at a side and released. It starts moving in a to and fro motion. This is called an oscillatory motion. The time taken by the pendulum to complete one oscillation is called time period. This time period is always same with a pendulum having same length. Time period changes with the change in the length of the string. The string of the pendulum is adjusted to the length, that it completes one oscillation in second and it keeps on moving the clock giving us time.

Motion and Time Class 7 HBSE Notes

• Motion is the change in the position of an object with respect to its surroundings.
• Motion can be of many types. It can be along a straight line, circular, oscillatory.
• Motion can be uniform or non-uniform motion.
• Uniform motion means equal distance covered in equal intervals of time. It means a constant motion.
• Non-uniform motion means unequal distance covered in equal intervals of time.
• Distance moved by an object in unit time is called its speed.
• Basic unit of measuring speed is (m/s) meter / second.
• Time is measured in respect to the periodic motions.
• Pendulum was the first device to measure time exactly.
• In earlier days time Was measured by various objects like sundials, sand clocks, water clocks, etc.
• With the discovery of pendulum, devices to measure exact time were invented.
• Now-a-days various devices like stop-watch and other electronic devices are used to measure time intervals smaller than even a second.
• Distance time graph gives us the an idea about the motion of the object. Straight line obtained on this graph depicts constant motion, while non-constant motion is depicted by various shapes on the graph.

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