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2. Electric Potential and Capacitance
easy
A charge $( - q)$ and another charge $( + Q)$ are kept at two points $A$ and $B$ respectively. Keeping the charge $( + Q)$ fixed at $B$, the charge $( - q)$ at $A$ is moved to another point $C$ such that $ABC$ forms an equilateral triangle of side $l$. The net work done in moving the charge $( - q)$ is
A
$\frac{1}{{4\pi {\varepsilon _0}}}\frac{{Qq}}{l}$
B
$\frac{1}{{4\pi {\varepsilon _0}}}\frac{{Qq}}{{{l^2}}}$
C
$\frac{1}{{4\pi {\varepsilon _0}}}Qql$
D
Zero
Solution
(d) According to figure, potential at $A$ and $C$ are equal. Hence work done in moving $-q$ charge from $A$ to $C$ is zero.
Standard 12
Physics
