There are four concentric shells A, B, C and D of radii a, 2a, 3a and 4a respectively. Shells B and D are given charges +q and –q respectively. Shell C is now earthed. The potential difference VA−VC is :
A
kq2a
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B
kq3a
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C
kq4a
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D
kq6a
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Solution
The correct option is Dkq6a It is clear from figure, q' charge given to the earth surface and also Vc=0 b=2a,c=3a,d=4a Vc=kq3a−kq4a+kq′3a=0 q′=−q4
Now, VA=kq2a−kq4a+kq′3a VA=kq6a