## Sunday, 2 July 2017

### class 12 cbsevWORKSHEET#2 ELECTRIC POTENTIAL AND CAPACITANCE

WORKSHEET#2 ELECTRIC POTENTIAL AND CAPACITANCE

2MARK
1)Draw E and V versus r on the same graph for a point charge.
2) Find position around dipole at which electric potential due to dipole is zero
but has non zero electric field intensity.
3) The electric potential V at any point in space is given V = 20x3 volt, where x is in
meter. Calculate the electric intensity at point P (1, 0, 2).
Ans. 60 NC.1
4)  Justify why two equipotential surfaces cannot intersect.
5Find equivalent capacitance between A and B in the combination given below : each capacitor is
of  2 µF. Ans. 6/7 µF
6) For an isolated parallel plate capacitor of capacitance C and potential difference V, what will be change in (i) charge on the plates (ii) potential difference across the  plates  (iii) electric field between the plates (iv)energy stored in the  capacitor, when the   distance between the plates is increased ?
Ans. (i) No change (ii) increases (iii) No change (iv) increases.
7) A RAM (Random access Memory) chip a storage capacitor has a capacity of 55pF. If the    capacitor is charged to 5.3V, how may excess electrons areon its negative plate ? Ans. 1.8 × 109
8) What is electric field between the plates with the separation of 2 cm and (i)with air (ii) dielectric medium of dielectricconstant K. Electric potentialof each plate is marked in the following figure.

9) The figure shows the Q (charge) versus V (potential) graph for a combination of two capacitors. identify the graph representing the parallel combination.

10) Calculate the work done in taking a charge of 1µC in a uniform electric field of 10 N/C from B to C given AB = 5 cm along  the field and AC = 10cm  perpendicular to electric field.
11) Two charges -q and + q are located at points A (0, 0, -a) and B (0, 0, + a) respectively. How much work is done in moving a test charge from pointP (7, 0, 0) to Q (-3, 0, 0) ? (zero)
12) The potential at a point A is -500 V and that at another point B is + 500 V. What is the work done by external agent to take 2 units (S.I.) of negative charge from B to A.
13)  How does the Potential energy of (i) mutual interaction (ii) net electrostatic P.E. of two charges change when they are placed in an external electric field.
14) With the help of an example, show that Farad is a very large unit of capacitance.
15)  What is meant by dielectric polarisation ? Why does the electric field inside  a dielectric decreases when it in placed in an external field ?
16) In charging a capacitor of capacitance C by a source of emf V, energy supplied by the sources QV and the energy stored in the capacitor is ½QV. Justify the difference.
3 Mark
1) Define electrostatic potential and its unit. Obtain expression for electrostatic potential at a point P in the field due to a point charge.
2)  Calculate the electrostatic potential energy for a system of three point charges placed at the corners of an equilateral triangle of side a
3)  What is polarization of charge ? With the help of a diagram show why the electric field between the plates of capacitor reduces on introducing a dielectric slab. Define dielectric constant on the basis of these fields.
4) Three capacitors are connected ®rst in series and then in parallel. Find the equivalent capacitance for each type of combination.
5) A charge Q is distributed over two concentric hollow sphere of radii r and R (R > r), such that their surface density of charges are equal. Find Potential at the common centre.
6) Derive an expression for the energy density of a parallel plate capacitor.
7) You are given an air filled parallel plate capacitor. Two slabs of dielectric constants K1 and K2 having been filled in between the two plates of the capacitor as shown in Fig. What will be the capacitance of the capacitor of initial area was A distance between plates d ?
8) A conducting slab of thickness .t. is introduced between the plates of a parallel plate capacitor, separated by a distance d (t < d). Derive anexpression for the capacitance of the capacitor. What will be its capacitance when t = d ?
9) If a dielectric slab is introduced between the plates of a parallel plate capacitor after the battery is disconnected, then  how do the followingquantities change.(i) Charge(ii) Potential(iii) Capacitance (iv) Energy.
10) What is an equipotential surface ? Write three properties Sketch equipotential surfaces of(i) Isolated point charge(ii  Uniform electric field(iii) Dipole
11) If charge Q is given to a parallel plate capacitor and E is the electric field between the plates of the capacitor the force  on each plate is 1/2 QE and if charge Q is placed between the plates experiences a force equal to QE. Give reason to explain the above.
12) Two metal spheres A and B of radius r and 2r whose centres are separated by a distance of 6r are given charge Q, are at potential V1 and V2. Find the ratio of V1/V2. These spheres are connected to each other with the help of wire connecting wire keeping the separation unchanged, with its the amount of charge that will flow through the?

13) Define potential gradient. How can potential gradient of a potentiometers be determined experimentally. In the graph shown here, a plot of potential drop versus length of the potentiometer is made for two potentiometers.B ?
Which is more sensitive A orB?