Electrostatics 3 Question 2

2. A solid conducting sphere, having a charge Q, is surrounded by an uncharged conducting hollow spherical shell. Let the potential difference between the surface of the solid sphere and that of the outer surface of the hollow shell be V. If the shell is now given a charge of 4Q, the new potential difference between the same two surfaces is

(a) 2V

(b) 2V

(c) 4V

(d) V

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Answer:

Correct Answer: 2. (c)

Solution:

  1. Initially when uncharged shell encloses charge Q, charge distribution due to induction will be as shown,

The potential on surface of inner shell is

VA=kQa+k(Q)b+kQb

where, k =proportionality constant.

Potential on surface of outer shell is

VB=kQb+k(Q)b+kQb

Then, potential difference is

ΔVAB=VAVB=kQ1a1b

Given,

ΔVAB=V

So, kQ1a1b=V

Finally after giving charge 4Q to outer shell, potential difference will be

ΔVAB=VAVB=kQa+k(4Q)bkQb+k(4Q)b=kQ1a1b=V [from Eq. 

Hence, we obtain that potential difference does not depend on the charge of outer sphere, hence potential difference remains same.



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