Question

Charges $Q_1$ and $Q_2$ are in vacuum initially. $Q_2$ experiences a net force F due to the presence of $Q_1$. They are now placed in a new medium of dielectric constant ε_rand the relative distance between them is maintained. The new net force experienced by $Q_2$ due to the presence of $Q_1$ is

• A. $\frac{F}{{\epsilon }_r}$
• B. $F{\epsilon }_r$
• C. $F(1+{\epsilon }_r)$
• D. Electrostatic force does not change with medium

Answer 1

The correct option is A

$\frac{F}{{\epsilon }_r}$

Net force on $Q_2$ in medium of relative permittivity ${\epsilon }_r$

$F_2=\frac{1}{4\pi {\epsilon }_r{\epsilon }_0}\frac{Q_1{Q}_2}{r_2}(\because {\epsilon }_r=\frac{{\epsilon }_{medium}}{{\epsilon }_0})\frac{F_2}{F}=\frac{\frac{1}{4\pi {\epsilon }_r{\epsilon }_0}\frac{Q_1{Q}_2}{r^2}}{\frac{1}{4\pi {\epsilon }_0}\frac{Q_1{Q}_2}{r^2}}{F}_2=\frac{F}{{\epsilon }_r}$