The energy stored in a capacitor is $W$. To double the charge on the plates of the capacitor, the additional work to be done is

A wire of length 10 m carrying current of 1 A is bent in to a circular loop. If a magnetic field of $2 \pi \times 10^{-4} \mathrm{~T}$ is applied on the loop, then the maximum torque acting on it is

The radii of the inner and outer spheres of a spherical capacitor are 8 cm and 9 cm respectively. The outer sphere is earthed and the inner sphere is charged. If the space between the concentric spheres is filled with a liquid of dielectric constant 5 , the capacitance of the capacitor is

A capacitor of capacitance $2 \mu \mathrm{~F}$ is charged to 50 V and then disconected from the source. Later the gap between the plates of the capacitor is filled with a dielectric material. If the energy stored in the capacitor is decreased by $25 \%$ of its initial value, then the dielectric constant of the dielectric material is