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NCERT Class XII Chapter
Electric Charges and Fields
Questions With Solutions

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Question : 2
Total: 34
The electrostatic force on a small sphere of charge 0.4 μC due to another small sphere of charge –0.8 μC in air is 0.2 N.
(a) What is the distance between the two spheres?
(b) What is the force on the second sphere due to the first?
Solution:  
Given, F12 = 0.2 N , q1 = 0.4 × 10−6 C , q2 = - 0.8 × 10−6 C
As, F12 =
1
4πε0
q1q2
r2
 or r2 =
1
4πε0
q1q2
F12
 = 9 × 109 ×
0.410−6×0.8×10−6
0.2
or r2 = 14.4 × 10−3 = 1.44 × 10−2
or r = 1.2 × 10−1 m = 12 cm
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