Question

Two point charges having equal charges separated by $1m$ distance experience a force of $8N$. What will be the force experienced by them, if they are held in water, at the same distance?
(Given, $K_{water}=80$ )

• A. $1N$
• B. $0.01N$
• C. $0.1N$
• D. $10N$

Answer 1

The correct option is C $0.1N$

$F=\frac{q_1{q}_2}{4\pi {ϵ}_{o}K{r}^2}$

For air, $K=1$ and hence $F=\frac{q_1{q}_2}{4\pi {ϵ}_o{r}^2}=8N$

In water:-

$F=\frac{q_1{q}_2}{4\pi {ϵ}_{o}K{r}^2}=\frac{8N}{k}=\frac{8}{80}$

$⟹F=0.1N$

Answer-(C)