Q. Two point charges placed at certain distance $r$ in air exert a force $F$ on each other. Then the distance $r^{'}$ at which these charges will exert the same force in a medium of dielectric constant $k$ is given by
A) $r$
B) $r/k$
C) $r/\sqrt{k}$
D) $r\sqrt{k}$
Explanation
(c) $F = F^{'}$ or $\frac{Q_{1}Q_{2}}{4\pi\varepsilon_{0}r^{2}\ } = \frac{Q_{1}Q_{2}}{4\pi\varepsilon_{0}r^{'2}\ K\ } \Rightarrow r^{'} = \frac{r}{\sqrt{K\ }}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.