Download class xii physics assignment

CLASS XII PHYSICS ASSIGNMENT
ELECTROSTATICS
Very short answer questions (1 mark)
1. If coulomb’s law involved 1/r3 dependence (instead of 1/r2), would Gauss’s law still hold?
2. What is frankline?
3. What is super capacitor?
4. Draw lines of force to represent uniform electric field.
5. Name two basic properties of electric charge.
6. An electrostatic field line cannot be discontinuous. Why?
7. A 500μC charge is at the centre of a square of side 10 cm. find the work done in moving a charge of 10 μC between
two diagonally opposite points on the square.
8. In which orientation, a dipole placed in a uniform electric field is in (i) stable equilibrium (ii) unstable equilibrium?
Short answer questions (2 or 3 marks)
1. Two identical point charges Q are kept at a distance r from each other. A third point charge q is placed on the line
joining the two charges, such that all three charges are in equilibrium. What is the sign, magnitude and position of
the third charge.
2. How pair production does show that the charge conserve?
3. What is the function of dielectric in a capacitor?
4. Two charged copper spheres of radii r and 2r are touched and then separated. Which sphere has larger (i) intensity
and (b) potential energy?
5. Calculate the Coulomb force between two α particles separated by a distance 3.2 X 10-15 m.
6. Can a metal sphere of radius 1 cm hold a charge of 1 coulomb? Justify your answer.
7. Calculate the potential at the centre of a square of side √2 m, which carries at its four corners charges of 2 μC, 1 μC,
-2 μC and -3 μC respectively?
8. An electric dipole is held in uniform electric field. Show that no translatory force acts on it. Derive an expression
for the torque acting on it.
9. Derive an expression for the torque experienced by an electric dipole kept in a uniform electic field.
10. Sketch a graph to show how charge Q given to a capacitor of capacity C varies with the potential difference V.
11. State Gauss’s theorem. Using Gauss’s theorem, derive an expression for the electric field intensity at any point
inside a hollow charged conducting sphere.
12. A parallel plate capacitor, each with plate area A and separation d is charged to a potential difference V and the
battery is disconnected. A dielectric slab of thickness d and dielectric constant K is placed between the plates. What
change, if any, will take place in (i) charge on plates (ii) electic field intensity between the plates (iii) capacitance.
13. An electic field of dipole moment P is placed in a uniform electic field E. Identify two pairs of perpendicular
vectors in the expression. Show diagrammatically the orientation of the dipole in the field for which the torque is (i)
maximum (ii) half the maximum value (iii) zero?
14. A metallic solid sphere is mounted on an insulating stand. Two metallic hemispheres, which fit exactly on the
surface of the solid sphere, are fitted with insulating handles. The solid sphere is first positively charged and then is
covered up with hemispheres. On removing the hemispheres what charges are expected on the solid sphere and the
hemispheres?
15. Work done to move a charge along a closed path inside an electric field is always zero, using this fact,
prove that it is impossible to produce an electric field in which all limes of force would be parallel lines
and density of their distribution would constantly increase in a direction perpendicular to the lines of
force.
Long Answer questions (5 marks)
1. Obtain the expression for the capacitance of a parallel plate capacitor. Three capacitors of capacitances C 1, C2 and
C3 are connected (i) in series (ii) in parallel. Show that the energy stored in the series combination is the same as
that in the parallel combination.
2. Derive an expression for the total energy stored in a parallel plate capacitor. Hence show that electric field E is a
source of energy with energy density ½ εoE2 Jm-3.