Q. Two positive point charges of $12\mu C\ and\ 8\mu C$ are $10\ cm$ apart. The work done in bringing them $4\ cm$ closer is
A) $5.8\ J$
B) $5.8\ eV$
C) $13\ J$
D) $13\ eV$
Explanation
(c) $W = U_{f} - U_{i} = 9 \times 10^{9} \times Q_{1}\ Q_{2}\left\lbrack \frac{1}{r_{2}} - \frac{1}{r_{1}} \right\rbrack$
$\Rightarrow W = 9 \times 10^{9} \times 12 \times 10^{- 6} \times 8 \times 10^{- 6}\left\lbrack \frac{1}{4 \times 10^{- 2}} - \frac{1}{10 \times 10^{- 2}} \right\rbrack$
$= 12.96\ J = 13\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.