Two spheres of radii r₁ and r₂ are charged to the same potential. If s₁ and s₂ are surface densities of charges on the two, then ratio  is

The work done in carrying a charge Q once round the circle of radius r with charge Q at the centre of the circle is

Electric potential of earth is taken to be zero because earth is a good

A capacitor of capacitance 2 μF is charged to a potential difference of 200 volts. After disconnecting from the battery, it is connected in parallel with another uncharged capacitor. The common potential is 40 volts. The capacitance of the second capacitor is