Question

Two charges of magnitude 5 nC and -2 nC, one placed at points (2 cm, 0, 0) and (x cm, 0, 0) in a region of space, where there is no other external field. If the electrostatic potential energy of the system is -0.5 $\mu$J. The value of x is:

• A. 20 cm
• B. 80 cm
• C. 4 cm
• D. 16 cm

Answer 1

Answer: (A)

20 cm

Potential energy of system $U=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{r}$

$=0.5\times {10}^{-6}=\frac{9\times {10}^9\times 5\times {10}^{-9}\times (-2)\times {10}^{-9}}{(x-2)\times {10}^{-2}}$

$\Rightarrow x=20cm$