MCQ:- Electric charge and field and Potential, Capacitance
The surface considered for Gauss’s law is called
(a) Closed surface (b) Spherical surface (c) Gaussian surface (d) Plane surface
A charge Q is placed at the centre of the line joining two point charges +q and +q as shown in the
figure. The ratio of charges Q and q is
(a) 4 (b) ¼ (c) -4 (d) -1/4
The SI unit of electric flux is
(a) N C-1 m-2 (b) N C m-2 (c) N C-2 m2 (d) N C-1 m2
The SI unit of electric flux is
(a) N C-1 m-2 (b) N C m-2 (c) N C-2 m2 (d) N C-1 m2
The work done in bringing a unit positive charge from infinite distance to a point at distance x from a
positive charge Q is W. Then the potential at that point is
Equipotential surfaces
(a) are closer in regions of large electric fields compared to regions of lower electric fields.(b)
will be more crowded near sharp edges of a conductor.
(c) will always be equally spaced. (d) both (a) and (b) are correct.
6. In a region of constant potential
(a) the electric field is uniform. (b) the electric field is zero.
(c) there can be no charge inside the region. (d) both (b) and (c) are correct.
7. A test charge is moved from lower potential point to a higher potential point. The potential
energy of test charge will
(a) remain the same (b) increase (c) decrease (d) become zero
8. An electric dipole of moment p⃗ is placed in a uniform electric field E⃗ . Then
(i) the torque on the dipole is p⃗ ×E→
(ii) the potential energy of the system is p⃗ .E→
(iii) the resultant force on the dipole is zero. Choose the correct option.
(a) (i), (ii) and (iii) are correct
(b) (i) and (iii) are correct and (ii) is wrong
(c) only (i) is correct
(d) (i) and (ii) are correct and (iii) is wrong
9. If a conductor has a potential V ≠ 0 and there are no charges anywhere else outside, then
(a) there must be charges on the surface or in¬side itself.
(b) there cannot be any charge in the body of the conductor.
(c) there must be charges only on the surface.
(d) both (a) and (b) are correct.
10. Which of the following statements is false for a perfect conductor?
(a) The surface of the conductor is an equipotential surface.
(b) The electric field just outside the surface of a conductor is perpendicular to the surface.
(c) The charge carried by a conductor is always uniformly distributed over the surface of the
conductor. (d) None of these.
11. Dielectric constant for a metal is
(a) zero (b) infinite (c) 1 (d) 10
12. When air is replaced by a dielectric medium of constant K, the maximum force of
attraction between two charges separated by a distance
(a) increases K times (b) remains unchanged (c) decreases K times
(d) increases K-1 times
13. In a parallel plate capacitor, the capacity increases if
(a) area of the plate is decreased. (b) distance between the plates increases.
(c) area of the plate is increased. (d) dielectric constantly decreases.
14. A parallel plate air capacitor is charged to a potential difference of V volts. After disconnecting the
charging battery the distance between the plates of the capacitor is increased using an insulating
handle. As a result the potential difference between the plates
(a) increases (b) decreases (c) does not change (d) becomes zero
15. Two identical capacitors are joined in parallel, charged to a potential V, separated and then
connected in series, the positive plate of one is connected to the negative of the other. Which of the
following is true?
(a) The charges on the free plated connected to-gether are destroyed.
(b) The energy stored in ths system increases.
(c) The potential difference between the free plates is 2V.
(d) The potential difference remains constant.
16. A capacitor has some dielectric between its plates, and the capacitor is connected to a dc
source. The battery is now disconnected and then the dielectric is removed, then
(a) capacitance will increase. (b) energy stored will decrease.
(c) electric field will increase. (d) voltage will decrease.
17. Two spherical conductors each of capacity C are charged to potential V and -V. These are
then connected by means of a fine wire. The loss of energy is
(a) zero
(b) 1/2CV2
(c) CV2
(d) 2 CV2
