Two charges q_1 and q_2 are placed at the centres of two spherical conducting shells of radius r_1 and r_2 respectively. The shells are arranged such…

Two charges $\displaystyle \mathrm{q}_{1}$ and $\displaystyle \mathrm{q}_{2}$ are placed at the centres of two spherical conducting shells of radius $\displaystyle \mathrm{r}_{1}$ and $\displaystyle \mathrm{r}_{2}$ respectively. The shells are arranged such that their centres are $\displaystyle \mathrm{d}\left[>\left(\mathrm{r}_{1}+\mathrm{r}_{2}\right)\right]$ distance apart. The force on $\displaystyle \mathrm{q}_{2}$ due to $\displaystyle \mathrm{q}_{1}$ is :