Before we start YOU must understand some part of LUCK also plays with your Questions. Here please go through 5 Marker Questions from FOREIGN and also PANCHKULA Boards !
you will find one part as shorter and simpler, while other is longer! here lies your quality to choose Questions WHERE you are MORE CONFIDENT !
ELECTROSTATICS
FOREIGN 2015
- Write the expression for the torque t acting on a dipole of dipole moment p placed in an electric field E [1]
- Four charges +q, – q, + q and – q are to be arranged respectively at the four corners of a square ABCD of side ‘a’. (a) Find the work required to put together this arrangement. (b) A charge q0 is brought to the center of the square, the four charges being held fixed. How much extra work is needed to do this? [3]
OR
Three point charges +q each are kept at the vertices of an equilateral triangle of side ‘l’. Determine the magnitude and sign of the charge to be kept at its centroid so that the charges at the vertices remain in equilibrium. [3]
- (a) A small conducting sphere of radius ‘r’ carrying a charge +q is surrounded by a large concentric conducting shell of radius R on which a charge +Q is placed. Using Gauss’s law, derive the expressions for the electric field at a point ‘x’.(i) between the sphere and the shell (r < x < R), (ii) outside the spherical shell. (b) Show that if we connect the smaller and the outer sphere by a wire, the charge q on the former will always flow to the latter, independent of how large the charge Q is. [5]
OR
(a) Consider a system of n charges q1, q2, … qn with position vectors r1 , r2 , r3 , … rn relative to some origin ‘O’. Deduce the expression for the net electric field E at a point P with position vector rp , due to this system of charges.
(b) Find the resultant electric field due to an electric dipole of dipole moment, 2aq, (2a being the separation between the charges ± q) at a point distant ‘x’ on its equator. [5]
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SOLUTION
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PANCHKULA 2015
- Write a relation for polarization P of a dielectric material in the presence of an external electric field E [1]
- Explain briefly the process of charging a parallel plate capacitor when it is connected across a d.c. battery. A capacitor of capacitance ‘C’ is charged to ‘V’ volts by a battery. After some time the battery is disconnected and the distance between the plates is doubled. Now a slab of dielectric constant,1 < k < 2, is introduced to fill the space between the plates. How will the following be affected:
(a) The electric field between the plates of the capacitor
(b) The energy stored in the capacitor
Justify your answer by writing the necessary expressions [3]
- (a) Deduce the expression for the potential energy of a system of two charges q1 and q2 located at r1 and r2 respectively in an external electric field.
(b) Three point charges, + Q, + 2Q and – 3Q are placed at the vertices of an equilateral triangle ABC of side l.
If these charges are displaced to the mid-points A1, B1 and C1 respectively (where ,A1, B1 and C1 are mid points of AB, BC and CA respectively) find the amount of the work done in shifting the charges to the new locations. [5]
OR
Define electric flux. Write its SI unit.
State and explain Gauss’s law. Find out the outward flux due to a point charge + q placed at the centre of a cube of side ‘a’. Why is it found to be independent of the size and shape of the surface [5]