Question

A uniformly charged sphere is placed as shown. Find the amount of work done by an external agent to bring a 2C charge (Very slowly without acceleration) from infinity to the point P? Take infinity as the reference

• A. $1.8\times {10}^{12}J$
• B. $1.8\times {10}^{11}J$
• C. $18\times {10}^{12}J$
• D. $1.8\times {10}^{14}J$

Answer 1

The correct option is A $1.8\times {10}^{12}J$

Potential due to the sphere at P is same as due to equal ‘Q’ placed at its centre.
Therefore , $V_p=\frac{KQ}{r}$ Here, Q=10 C and r=10 cm=0.1 m
Implies, $V_P=9\times {10}^{11}J/C$
So the work done by the external agent in bringing 2C charge to point $P=2V_p=1.8\times {10}^{12}J$