Class 8 Maths


Exponents and Power

Exercise 12.2

Question 1: Express the following numbers in standard form

(a) 0.0000000000085

Answer: 8.5 × 10-12

(b) 0.00000000000942

Answer: 9.42 × 10-12

(c) 6020000000000000

Answer: 6.02 × 1015

(d) 0.00000000837

Answer: 8.37 × 10-9

(e) 31860000000

Answer: 3.186 × 1010

Question 2: Express the following numbers in usual form

(a) 3.02 × 10-6

Answer: 0.00000302

(b) 4.5 × 104

Answer: 45000

(c) 3× 10-8

Answer: 0.000000003

(d) 1.0001× 106

Answer: 1000100

(e) 5.8× 1012

Answer: 5800000000000

(f) 3.61492 × 106

Answer: 3614920

Question 3: Express the number appearing in the following statements in standard form

(a) 1 micron is equal to `1/(1000000) m

Answer: 1 × 10-6 m

(b) Charge of an electron is 0.000, 000, 000, 000, 000, 000, 16 coulomb

Answer: 1.6 × 10-19

(c) Size of a bacterium is 0.0000005 m

Answer: 5 × 10-7 m

(d) Size of a plant cell is 0.00001275 m

Answer: 1.275 × 10-5

(e) Thickness of a thick paper is 0.07 mm

Answer: 7 × 10-2 mm

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: Total thickness of 5 books = 20 × 5 = 100 mm

Thickness of 5 sheets = 0.016 × 5 = 0.08 mm

Total = 100 + 0.08 = 100.08 mm

= 1.0008 × 10-2