$A$ hollow metal sphere has a radius $r$. The potential difference between a point on its surface and a point at a distance $3r$ from its center is $V$. The electric intensity at the distance $3r$ from the center of the sphere will be

Three capacitors $C_{1} = 2 \, \mu F$,$C_{2} = 6 \, \mu F$,and $C_{3} = 12 \, \mu F$ are connected as shown in the figure. Find the ratio of the charges on capacitors $C_{1}$,$C_{2}$,and $C_{3}$ respectively.

The switch $K$ is closed. Now,the switch $K$ is opened and both capacitors are filled with a dielectric of constant $K = 3$. What is the ratio of the energy of the system when the switch is closed to when it is open,$\frac{U_1}{U_2}$?

The potential difference between the points $P$ and $Q$ in the adjoining circuit will be :-

The charge deposited on the $4 \mu F$ capacitor in the circuit is

$A$ composite parallel plate capacitor is made up of two different dielectric materials with different thicknesses ($t_{1} = 0.5 \text{ mm}$ and $t_{2} = 1 \text{ mm}$) and dielectric constants ($\epsilon_{r1} = 3$ and $\epsilon_{r2} = 4$) as shown in the figure. The two dielectric materials are separated by a conducting foil $F$. The voltage of the conducting foil is $.....V$.