If an electric field near the earth surface be $300 {\mathrm{Vm}}^{-1}$ directed downwards, what is the surface density on earth's surface?

(i) Calculate the charge enclosed by the Gaussian surface,

An electric flux of $6\times {10}^3 {\mathrm{Nm}}^2{\mathrm{C}}^{-1}$ passes through a spherical Gaussian surface of radius $10 \mathrm{cm}$ due to the charge placed at its centre.

If the radius of the Gaussian surface is doubled how much flux would pass through the surface?

A sphere of metal has a radius of $12 \mathrm{cm}$ and carries a charge of $1.6\times {10}^{-7}\mathrm{C}$, distributed uniformly on its surface. Calculate the electric field intensity at a point inside the sphere.