Question

A ring of radius $6cm$ is given a charge $10$ $\mu$C. How much work will be done in transporting a charge of $6$ $\mu$C from its centre to a point $8cm$ along its axis?

• A. $63mJ$
• B. $84mJ$
• C. $105mJ$
• D. $360mJ$

Answer 1

Answer: (D)

$360mJ$

The potential of a ring along the axis is $\frac{kQ}{r}$

where $r$ is the distance of point of interest to the circumference of ring.

Hence work done in moving charge from center to the given point=$q(\frac{kQ}{r_2}-\frac{kQ}{r_1})$

$=-9\times {10}^9\times 10\times {10}^{-6}\times 6\times {10}^{-6}(\frac{1}{0.6}-\frac{1}{\sqrt{{0.6}^2+{0.8}^2}})$

$=360mJ$