NCERT Solution For Class 8 Math Chapter – Exponents and Power Exercise – 12.2
Q1. Express the following numbers into standard form.
- 0000000000085
- 00000000000942
- 6020000000000000
- 00000000837
- 31860000000
Solution:-
(i)
= 0.0000000000085 x (1012 / 1012) = 8.5 x 10-12
(ii)
= 0.00000000000942 x (1012/1012) = 9.42 x 10-12
(iii)
= 6020000000000000 x (1015/1015) = 6.02 x 1015
(iv)
= 0.00000000837 x (109/109) = 8.37 x 10-9
(v)
= 31860000000 x (1010 / 1010) = 3.186 x 1010
Q2. Express the following numbers in usual form.
- 02 x 10-6
- 5 x 104
- 3 x 10-8
- 001 x 109
- 8 x 1012
- 61492 x 106
Solution:-
(i)
= 3.02/106 = 0.00000302
(ii)
= 4.5 x 10000 = 450000
(iii)
= 3/108 = 0.00000003
(iv)
= 5.8 x 100000000000 = 58000000000000
(v)
= 3.61492 x 1000000 = 3614920
(vi)
= 1000100000
Q3. Express the number appearing in the following statements in standard form.
- 1 micron is equal to 1/1000000 m.
- Charge of an electron is 0.000 , 000 , 000 , 000 , 000 , 000 , 16 coulomb.
- Size of bacteria is 0.0000005 m
- Size of a plant cell is 0.00001275 m.
- Thickness of a thick paper is 0.07 mm.
Solution:-
- 1 micron = 1/1000000
= 1/106
= 1 x 10-6
- Charge of an electron is 0.00000000000000000016 coulombs.
= 0.00000000000000000016 x 1019 / 1019
= 1.6 x 10-19 coulomb
- Size of bacteria = 0.0000005
5/10000000 – 5/107 = 5 x 10-7 m
- Size of a plant cells 0.00001275 m
= 0.0000001275 x 105/105
= 1.275 x 10-5 m
- Thickness of a thick paper = 0.07 mm
0.07 mm = 7/100 mm = 7/102 = 7 x 10-2 mm
Q4. 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 ?
Solution:-
Thickness of one books = 20 mm
Thickness of 5 books = 20 x 5 = 100 mm
Thickness of paper = 0.016 mm
Thickness of 5 papers = 0.016 x 5 = 0.08
Total thickness of a stack = 100 + 0.08 = 100.08 mm
= 100.08 x 102/102 mm
= 1.0008 x 102 mm
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