Define gravitational field clearly.
Define electric field clearly.
State a similarity and a difference between the gravitational potential from a point mass and the electric potential from a point charge.
A uniform isolated conducting sphere has mass $M$ and charge $Q$. At its surface, the gravitational field strength is $g$, and the electric field strength is $E$. Show that $\frac{M}{Q} = \alpha \frac{g}{E}$, where $\alpha$ is a constant.
Show that $\alpha$ has the numerical value $1.35 \times 10^{20}\,\text{kg}^2\,\text{C}^{-2}$.
Treat the Earth as a uniform conducting sphere with mass $5.98 \times 10^{24}\,\text{kg}$. Its surface carries an evenly spread charge of $-4.80 \times 10^5\,\text{C}$. Use the result in (b) to determine the electric field strength at the Earth's surface. State a unit with your answer.
State how the direction of the electric field at the Earth's surface compares with that of the gravitational field.