Class 12 Physics 2018 Board Exam

Draw the pattern of electric field lines, when a point charge – Q is kept near an uncharged conducting plate.

Draw the pattern of electric field lines when a point charge +q is kept near an uncharged conducting plate.

Draw the equipotential surfaces due to an isolated point charge.

Define electric flux. Is it a scalar or a vector quantity ?
A point charge q is at a distance of d/2 directly above the centre of a square of side d, as shown in the figure. Use Gauss' law to obtain the expression for the electric flux through the square.
(b) If the point charge is now moved to a distance 'd' from the centre of the square and the side of the square is doubled, explain how the electric flux will be affected.
OR
(a) Use Gauss' law to derive the expression for the electric field (E) due to a straight uniformly charged infinite line of charge density λ C/m.
(b) Draw a graph to show the variation of E with perpendicular distance r from the line of charge.
(c) Find the work done in bringing a charge q from perpendicular distance r₁ to r₂ (r₂ > r₁).

Derive an expression for the electric field at any point on the equatorial line of an electric dipole.
(b) Two identical point charges, q each, are kept 2m apart in air. A third point charge Q of unknown magnitude and sign is placed on the line joining the charges such that the system remains in equilibrium. Find the position and nature of Q.

Find the resultant electric force on a charge Q, and potential energy of this system for four point charges Q, q, Q and q placed at the corners of a square of side 'a'.
OR
(a) Three point charges q, – 4q and 2q are placed at the vertices of an equilateral triangle ABC of side 'l'. Obtain the expression for the magnitude of the resultant electric force acting on the charge q.
(b) Find out the amount of the work done to separate the charges at infinite distance.

Draw the equipotential surfaces corresponding to a uniform electric field in the z-direction.
(b) Derive an expression for the electric potential at any point along the axial line of an electric dipole.

Draw equipotential surfaces corresponding to the electric field that uniformly increases in magnitude along with the z-directions.
(b) Two charges – q and + q are located at points (0, 0, – a) and (0, 0, a). What is the electrostatic potential at the points (0, 0, + z) and (x, y, 0) ?

Draw the equipotential surfaces due to an electric dipole.
(b) Derive an expression for the electric field due to a dipole of dipole moment p at a point on its perpendicular bisector.

Describe briefly the process of transferring the charge between the two plates of a parallel plate capacitor when connected to a battery. Derive an expression for the energy stored in a capacitor.
(b) A parallel plate capacitor is charged by a battery to a potential difference V. It is disconnected from battery and then connected to another uncharged capacitor of the same capacitance. Calculate the ratio of the energy stored in the combination to the initial energy on the single capacitor.