8TH MATHS PART 2 CHAPTER 2 EXPONENTS AND POWERS-3 EXERCISE 2.2
NCERT MATHS PART 2 CHAPTER 2
EXPONENTS AND POWERS EXERCISE 2.2
SOLUTIONS
Question 1:
Express the following numbers in standard form.
(i) 0.0000000000085 (ii) 0.00000000000942
(iii) 6020000000000000 (iv) 0.00000000837
(v) 31860000000
ANSWER:
(i) 0.0000000000085 = 8.5 × 10−12
(ii) 0.00000000000942 = 9.42 × 10−12
(iii) 6020000000000000 = 6.02 × 1015
(iv) 0.00000000837 = 8.37 × 10−9
(v) 31860000000 = 3.186 × 1010
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Question 2:
Express the following numbers in usual form.
(i) 3.02 × 10−6 (ii) 4.5 × 104
(iii) 3 × 10−8 (iv) 1.0001 × 109
(v) 5.8 × 1012 (vi) 3.61492 × 106
ANSWER:
(i) 3.02 × 10−6 = 0.00000302
(ii) 4.5 × 104 = 45000
(iii) 3 × 10−8 = 0.00000003
(iv) 1.0001 × 109 = 1000100000
(v) 5.8 × 1012 = 5800000000000
(vi) 3.61492 × 106 = 3614920
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Question 3:
Express the number appearing in the following statements in standard form.
(i) 1 micron is equal to 
m.
(ii) Charge of an electron is 0.000, 000, 000, 000, 000, 000, 16 coulomb.
(iii) Size of a bacteria is 0.0000005 m
(iv) Size of a plant cell is 0.00001275 m
(v) Thickness of a thick paper is 0.07 mm
ANSWER:
(i) 
= 1 × 10−6
(ii) 0.000, 000, 000, 000, 000, 000, 16 = 1.6 × 10−19
(iii) 0.0000005 = 5 × 10−7
(iv) 0.00001275 = 1.275 × 10−5
(v) 0.07 = 7 × 10−2
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Question 4:
In a stack there are 5 books each of thickness 20 mm and 5 paper sheets each of thickness 0.016 mm. What is the total thickness of the stack?
ANSWER:
Thickness of each book = 20 mm
Hence, thickness of 5 books = (5 × 20) mm = 100 mm
Thickness of each paper sheet = 0.016 mm
Hence, thickness of 5 paper sheets = (5 × 0.016) mm = 0.080 mm
Total thickness of the stack = Thickness of 5 books + Thickness of 5 paper sheets
= (100 + 0.080) mm
= 100.08 mm
= 1.0008 × 102 mm