A small sphere carrying a charge ‘$q$’ is hanging in between two parallel plates by a string of length $L$. Time period of pendulum is ${T_0}$. When parallel plates are charged, the time period changes to $T$. The ratio $T/{T_0}$ is equal to

Two spherical conductors $A$ and $B$ of radii $a$ and $b$ $(b > a)$ 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

When a lamp is connected in series with capacitor, then

In a spherical condenser radius of the outer sphere is $R$. The different in the radii of outer and inner sphere in $x$. Its capacity is proportional to

The capacity of a parallel plate condenser is $15\,\mu \,F$, when the distance between its plates is $6 \,cm$. If the distance between the plates is reduced to $2\, cm$, then the capacity of this parallel plate condenser will be......$\mu \,F$

Two capacitors $C_1$ and $C_2$ are charged to $120\ V$ and $200\ V$ respectively. It is found that connecting them together the potential on each one can be made zero. Then