Question

A system consists of two charges 4 $\mu C$ and -3 $\mu C$ with no external field placed at (-5 cm, 0, 0) and (5 cm, 0, 0) respectively. The amount of work required to separate the two charges infinitely away from each other is

• A. 1.1 J
• B. 2 J
• C. 2.5 J
• D. 3 J

Answer 1

The correct option is A 1.1 J

Here $q_1=4\mu C,q_2=-3\mu C,r=10cm=0.1m$

Electrostatic potential energy

$U_i=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{r}=9\times {10}^9\times \frac{4\times {10}^{-6}\times (-3)\times {10}^{-6}}{0.1}=-1.1J$

$U_f=0$

Work required, $W=U_f-U_i=0-(-1.1)=1.1$