Question

At 12 cm in the radial direction from a conductive sphere of radius 10 cm, the electric field is 1800 N/C and its orientation points towards the interior of the sphere. Find the surface density of the charge on the sphere.

Answer 1

$E=\frac{kqr}{R^3},$

$q=\sigma S=4\pi \sigma R^2,$

$E=\frac{4\pi kr\sigma}R,$

$\sigma=\frac{ER}{4\pi kr}=0.24~\frac{\mu C}{m^2}.$