A hollow cylinder has charge $q$ $C$ within it. If $\phi $ is the electric flux in unit of voltmeter associated with the curved surface $B$, the flux linked with the plane surface $A$ in unit of voltmeter will be

If the distance between the plates of a capacitor having capacity $C$ and charge $Q$ is doubled then work done will be

Two identical balls having like charges and placed at a certain distance apart repel each other with a certain force. They are brought in contact and then moved apart to a distance equal to half their initial separation. The force of repulsion between them increases $4.5$ times in comparison with the initial value. The ratio of the initial charges of the balls is

A negative charged particle is released from rest in a uniform electric field. The electric potential energy of charge

Three charges $2q,\, – q,\, – q$ are located at the vertices of an equilateral triangle. At the centre of the triangle