The electric field due to a charged conducting sphere of radius $10 \mathrm{cm},$, at a distance of $20 \mathrm{cm}$ from the centre of the sphere is $1.5 \times {10}^3 {\mathrm{NC}}^{-1 }$and points radially inwards. What is the charge on the sphere?

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

(i) inside the sphere,

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 just outside the sphere. 

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 $18 \mathrm{cm}$ from the centre of the sphere.