Question

A force ‘F’ is acting between two charges in air. If the space between them be completely filled with a medium $K=4$, the force will be :

• A. $F$
• B. $4F$
• C. $\frac{F}{4}$
• D. $2F$

Answer 1

Answer: (C)

By Coulomb's law, the force between two charges $(q_1,q_2)$ in air is given by $F=\frac{q_1{q}_2}{4\pi {ϵ}_0{r}^2}$

where $r=$ distance between two charges.

Now the force between two charges $(q_1,q_2)$ in medium with dielectric constant $K=4$ becomes, $F^{\prime }=\frac{q_1{q}_2}{4\pi K{ϵ}_0{r}^2}$

So, $F^{\prime }=\frac{F}{K}=\frac{F}{4}$