Question

Two insulated charged metallic spheres $P$ and $Q$ have their centres separated by a distance of $60 \,cm$. The radii of $P$ and $Q$ are negligible compared to the distance of separation. The mutual force of electrostatic repulsion if the charge on each is $3.2 \times 10^{-7}\, C$ is

• A. $5.2 \times 10^{-4}\, N$
• B. $2.5 \times 10^{-3}\, N$
• C. $1.5 \times 10^{-3}\, N$
• D. $3.5 \times 10^{-4}\, N$

Answer 1

Answer: (B)

Here, $q_1 = q_2 = 3.2 \times 10^{-7}\, C$, $r = 60\, cm = 0.6 \,m$
Electrostatic force,
$F=\frac{1}{4\pi\varepsilon_{0}r^{2}} \frac{q_{1}\,q_{2}}{r^{2}}=\frac{9\times10^{9}\left(3.2\times10^{-7}\right)^{2}}{\left(0.6\right)^{2}}$
$=25.6\times10^{-3}\,N$