Birla Public School, Pilani (Raj.)
Summer Vacation Assignment, 2015.
Class XII - Physics
1. Write the S.I unit of i.) electric field intensity ii.) Electric dipole moment.
iii) Electric Potential
2. How does the coulomb force between two point charges depend upon the dielectric
constant of the intervening medium?
3. Draw an equipotential surface for a system, consisting of two charges Q, -Q separated by
a distance ‘r’ apart.
4. Show graphically the variation of charge ‘q’ with time’t’ when a condenser is charged.
5. What orientation of an electric dipole in a uniform electric field would correspond to
stable equilibrium?
6. The potential energy of an electric dipole placed in a uniform electric field is minimum.
What is the orientation of vectors p and E?
7. State one situation in where potential is not zero but electric field intensity is zero .
8. Does the electric potential increase or decrease along an electric line of force?
9. A Gaussian surface encloses no charge. Does it mean that E = 0 on its surface?
10. At what point is the electric dipole field intensity (i) parallel and (ii) anti parallel to
dipole moment of the dipole?
11. A 10µC charge is at the centre of a square of side 10 cm. Find the work done in moving
the charge of 4 C between two diagonally opposite points on the square .
12. A charged air capacitor has stored energy U. What will be the energy stored when air is
replaced by a dielectric of dielectic constant K, charge Q remains the same ?
13. The sequence of bands marked on carbon resistor are Red, Red , Red , Silver . Write
the value of resistance with tolerance.
14. Define electric field intensity. Write its S.I. unit. Write the magnitude and direction of
electric field intensity due to an electric dipole of length 2a at the mid point of the line
joining the two charges.
15.. The force of attraction between two point charges placed at distance d apart in a
medium is F. What should be the distance apart in the same medium so that the force of
attraction between them becomes F/4?
16. Name the physical quantity whose SI unit is (i) coulomb/ volt (ii) newton/coulomb(iii)
joule/coulomb.
17. What is the amount of work done in moving a 56 nC charge between two points 1 cm
apart on an equipotential surface?
18.What would be the work done if a point charge +q, is taken from a point A to the point
B on the circumstance of a circle drawn with another point charge +q at the center ?
19.Two test charges are brought separately near a charge +Q.
Case 1: Test charge +q are brought to within a distance r from the charge +Q (i.e. to point
A).
Case 2: Test charge +2q are brought to within a distance 2r from the charge +Q (i.e. to
point B).
1. In which situation is the Electric Potential Energy of the system the greatest?
2. At which position is the Electric Potential the greatest
Questions having two mark each
1. Two point charges, q =8×10-8 C and Q= -2×10-8 C are separated by a distance of 10 cm in
air.
a) Find at what distance from the Q, would the electric potential be zero.
b) What is the net electric field at the mid point between the charges
2). Two capacitors of capacitance 10µF and 12µF are connected in series with a battery.
The voltage across the 12µF capacitor is 10V. Compute the total battery voltage..
3) Electric charge is distributed uniformly on the surface of a spherical shell. Explain the
variation Of Electric potential and electric Field intensity
i. on the surface
ii. Inside and
iii. Outside
4) Derive an expression for the energy stored in a parallel plate capacitor C , charged to
potential difference V .
5) Two equally charged identical metal spheres X and Y repel each other with a force of F
N. Another identical uncharged sphere Z is touched to X and then placed at the mid point
between X and Y. What is the net force on Z?
6) The total capacitance of two capacitors is 4µfwhen connected in series and 18µf
when connected in parallel. Find the capacitance of each capacitor?
7) A parallel plate capacitor is charged to a certain potential difference. When a 3 mm
thick slab is slipped between the capacitor plates then to maintain the same Potential
difference between the plates, the plate separation has to be increased by 2.4 mm. Find the
dielectric constant of the slab
Questions Having 5 marks each
1. Explain the principle on which Van-de-Graaff generator operates. Draw a labeled
schematic sketch and write briefly it’s working.
2. An electric dipole is held in a uniform electric field.
i. Show that no translatory force acts on it.
ii. Derive an expression for the torque acting on it.
iii. The dipole is aligned parallel to the field. Calculate the work done in rotating it through
180 degree
3) A parallel plate capacitor is charged by a battery. After sometime the battery is
disconnected and a dielectric slab with its thickness equal to the plate separation is inserted
between the plates.
What is the impact on these quantities?
(i) The capacitance of the capacitor
(ii) Potential difference between the plates
(iii) The energy stored in the capacitor
4. Use Gauss theorem to derive an expression for the electric field at a point due to
a. an infinite plane sheet of charge of uniform charge density ?
b. a thin infinitely long straight line of charge of uniform charge density ?
5. There are two identical particles each of mass m and carrying charge Q. Initially one of
them is at rest and another charge moves with velocity v directly towards the particle at
rest. Find the distance of closest approach.