(a(i))[1]
State the meaning of a line of force in a gravitational field.
(a(ii))[2]
State the meaning of a line of force in an electric field.
(b)[3]
A charged metal sphere is isolated in space. State one similarity and one difference between the gravitational force field and the electric force field around the sphere.
(c)[4]
Two horizontal metal plates are separated by $1.8\text{ cm}$ in a vacuum. A potential difference of $270\text{ V}$ is kept between the plates, as shown in Fig. 3.1. A proton is located in the region between the plates. Explain quantitatively why the gravitational field is ignored when predicting the motion of the proton between the plates.