A long hollow conducting cylinder is kept coaxially inside another long, hollow conducting cylinder of larger radius. Both the cylinders are initially electrically neutral. 

If $g_E$ and $g_M$ are the accelerations due to gravity on the surfaces of the Earth and the Moon respectively and if Millikan's oil drop experiment could be performed on the two surfaces, one will find the ratio $\frac{\text{electronic }\text{charge }\text{on }\text{the }\text{moon }}{\text{electronic }\text{charge }\text{on }\text{the }\text{earth }}$  to be

In the following figure, three paths of $\alpha$ particle crossing a nucleus $N$ are shown. The correct path is 

(a) 

(b) 

(c) 

A conducting sphere of radius $10 \mathrm{cm}$ is charged to $10 \mu \mathrm{C}$. Another uncharged sphere of radius $20 \mathrm{cm}$ is allowed to touch it for some time. After that, if the spheres are separated, then surface density of charges on the spheres will be in the ratio of

Two spherical conductors $A_1$ and $A_2$ of radii $r_1$ and $r_2$ are placed concentrically in air. The two are connected by a copper wire as shown in figure. Then the equivalent capacitance of the system is

A dipole having moment $P$ is placed in front of a solid uncharged conducting sphere as shown in the diagram. The net potential at point $A$ lying on the surface of the sphere is