UT-1 (2022-2023)
Class-XII
Subject-Physics
MM: 25
Part – A (2×4=8)
1. Find the total energy in the capacitors in the network.
2. a) Draw an equipotential surface for two positive charges.
b) The figure shows lines of constant potential in a region in which an electric field exists. The value of the potential are indicated. Out of the points A, B and C, which will be the greatest electric field strength? Give a reason.
3. A thin metallic spherical shell of radius R carries a charge Q on its surface. A point charge Q/2 is placed at its center C and another charge +2Q is placed outside the shell at a distance x from the centre as shown in the figure.
a) Find the electric flux through the shell.
b) Find the force on the charges at the centre C of the shell and at a point A.
4. Explain the term polarization of the dielectric. List the factors on which the extent of polarization depends.
Part – B
5. a) A parallel plate capacitor of capacitance C is charged to a potential V by a battery. Without disconnecting the battery, distance between the plates of capacitor is tripled and a dielectric medium of K=10 is introduced between the plates of capacitor. Explain giving reasons how will the following be affected?
i) Capacitance of the capacitor
ii) Charge on the capacitor
iii) The electric field between the plates of the capacitor.
6. a) Can electrostatic potential at a point be zero while the electric field at that point is not zero?
b) Find the amount of work done in rotating an electric dipole moment 3.2×10^-8 Cm from its position of stable equilibrium to the position of unstable equilibrium in a uniform electric field of intensity 10^4 N/C.
7. a) Figure shows three point charges +2q, -q and +3q. Two charges +2q and -q are enclosed within a surface S.
What is the electric flux due to this configuration through the surface S?
b) Two identical metal spheres having equal and similar charges repel each other with a force of 103 N when they are 10 cm apart in a medium of dielectric constant 5. Determine the charge on each sphere.
8. a) A metal plate is introduced between the plates of a charged parallel plate capacitor. Sketch the electric line of force between the plates.
b) The plates of a parallel plate capacitor have an area of 90 sq. cm each and are separated by 2.5 mm. The capacitor is charged by connecting it to a 400 V supply. How much electrostatic energy is stored by the capacitor?
Part – C
9. a) Use Gauss Law to obtain an expression for the electric field due to an infinitely long straight uniformly positively charged wire.
b) Electric field in the given figure is directed along +X direction and given by Ex=5Ax+2B, where E is in NC-1 and x is in metre, A and B are constants with dimensions. Taking A=10 NC-1m-1 and B=5 NC-1m-1. Calculate the electric flux through the cube.
