**Electrostatic Potential and Capacitance**

Max. Marks :: 30 Time:: 75 minutes

**1 mark questions**

- Define electric potential.
- Define 1 farad.
- State the principle of a capacitor.
- Draw the equipotential surface for a point charge q>0.
- Define dielectric constant of a medium on the basis of capacitance.
- Write the ratio of electric potential at a distance r on equatorial position to the electric potential at a distance r on axial position.
- Calculate the radius of a spherical conductor of capacitance 1 pF.
- What is electrostatic shielding?
**2 Marks Questions** - A regular hexagon of side 10 cm has a charge 5 μC at each of its vertices. Calculate the potential at the centre of the hexagon.
- Derive an expression for the energy stored in a capacitor.
- Four capacitors are connected as shown in diagram. Calculate the equivalent capacitance between the points X and Y.

- When two capacitors of capacitance C
_{1}and C_{2}are connected in series, the net capacitance is 3μF . When connected in parallel the effective capacitance is 16μF. Calculate the values of C_{1}and C_{2}**3 marks questions** - Derive an expression for the capacitance of a parallel plate capacitor with a dielectric slab of thickness less than the spacing between the the plates inserted between the plates.
- A 10μF capacitor is charged by a 30V dc supply and then connected across a an uncharged 50μF capacitor. Calculate (i) the final potential difference across the combination, and (ii) the initial and final energies. How will you account for the difference in energy?
- A parallel plate capacitor with air between the plates has a capacitance of 8 pF. What will be the capacitance if the distance between the plates is reduced by half and the space betwee them is filled with a substance of dielectric constant K = 6?
**5 Marks Questions** - Describe the principle construction and working of a Van de Graff generator. Explain why the apparatus is enclosed inside a steel chamber maintained at high pressure.