1. Calculate the capacitance of two conductors carrying equal and opposite charges in terms of the coefficient of potential.

2.Three concentric shells of radii respectively carry charges and . Calculate the energy of the system.

3. Two concentric spherical shells of radii are both grounded and a point charge q is placed at a distance r between them, being insulated from both the surfaces. Calculate the energy of the system charges.

4. Calculate the work done in doubling the separation between the plates of a parallel plate capacitor from d to 2d, if the potential difference between the plates remains