Question

The force between two short electric dipole placed on the same axis at a distance R, varies as?

• A. $R^{-1}$
• B. $R^{-2}$
• C. $R^{-3}$
• D. $R^{-4}$

Answer 1

The correct option is D $R^{-4}$

The $F=\frac{1}{4\pi {ϵ}_0}\frac{q_1{q}_2}{r^2}=\frac{1}{4\pi {ϵ}_0}\frac{q_1\times r\times q_2\times r}{r^2\left(r^2\right)}$

$F=\frac{1}{4\pi {ϵ}_0}\frac{q_1{q}_2{r}^2}{r^4}$

where $\hat{r}=$ unit vector

$F\alpha \frac{1}{r^4}$

$F\alpha r^{-4}$