Question

Two point charges $+5\mu C$ and $-2\mu C$ are kept at a distance of $1m$ in free space. The distance between the two zero potential points on the line joining the charges is

• A. $\frac{2}{7}m$
• B. $\frac{2}{3}m$
• C. $\frac{22}{21}m$
• D. $\frac{20}{21}m$
• E. $\frac{8}{21}m$

Answer 1

Answer: (C)

Let the potential be zero at P and Q. Then solving for
$x_1$
$\frac{k\times 5}{x_1}=\frac{2k}{(1-x_1)}$
$x_1=\frac{5}{7}$
Similarly, $\frac{k\times 5}{1+x_2}=\frac{k\times 2}{x_2}$
$\therefore$ $x_2=\frac{2}{3}$
Separation $PQ=\left(1-\frac{5}{7}\right)+\frac{2}{3}$
$=\frac{20}{21}$