If 27 indentical charged conducting spheres each of capacitance $10 \mu \mathrm{~F}$ combine to form a big sphere, then the capacitance of the big sphere is

The capacitance of a spherical capacitor is 100 pF . If the spacing between the two spheres is 1 cm , then the radius of the inner sphere of the capacitor is

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