Question

Two identical thin rings each of radius r are coaxillary placed at a distance r have equal charge q each. Work done in moving a charge q' from the centre of one ring to that of the other is?

• A. Infinity
• B. $\frac{q^2}{4\pi {\epsilon }_{0}r}$
• C. Zero
• D. $\frac{q{q}^{\prime }}{4\pi {\epsilon }_{0}r}$

Answer 1

Answer: (C)

Zero

As the rings are identical and having same charge, so the electric potential at the centre of both the rings are equal. Hence, the potential difference between the centre of these rings is zero. i.e, $V=0$
Thus, the work done in moving a charge q' between these rings(centres) is
$W=-\frac{V}{q}=\frac{0}{q^{\prime }}=0$.