Electrostatic Fields MCQ

1. A parallel-plate capacitor with air between the plates has a capacitance of 10 pF. If the distance between the parallel plates is halved and the space between the plates is filled with a material of dielectric constant 5, the newly formed capacitor will have a capacitance of

  1. 50 pF
  2. 10 pF
  3. 150 pF
  4. 100 pF

Answer. d

2. The maximum potential-gradient that can be imposed in air at atmospheric pressure without breakdown is 30 kV/cm. The corresponding energy density is nearly

  1. 30 J/m3
  2. 35 J/m3
  3. 40 J/m3
  4. 45 J/m3

Answer. c

3. If a positively charged body is placed inside a spherical hollow conductor, what will be the polarity of charge inside and outside the hollow conductor?

  1. Inside positive, outside negative
  2. Inside negative, outside positive
  3. Both negative
  4. Both positive

Answer. b

4. “Electrical flux enclosed by a surface surrounding a charge is equal to the amount of charge enclosed.” This is the statement of

  1. Faraday’s law
  2. Lenz’s law
  3. Modified Ampere’s law
  4. Gauss’s law

Answer. d

5. Gauss’s theorem states that total electric flux emanating from a closed surface is equal to

  1. total current density on the surface
  2. total charge enclosed by that surface
  3. total current on the surface
  4. total charge density within the surface

Answer. b

6. The dielectric strength of rubber is 40000 V/mm at frequency of 50 Hz. What is the thickness of insulation required on an electrical conductor at 33 kV to sustain the breakdown?

  1. 0.83 mm
  2. 8.3 mm
  3. 8.3 cm
  4. 0.083 mm

Answer. a

7. Consider the following types of transmission lines:

  1. Open-wire line
  2. Twin-lead wire
  3. Coaxial cable

The capacitance per metre will be least in which of the above transmission lines?

  1. ii only
  2. i only
  3. i, ii and iii
  4. iii only

Answer. b

8. The capacitance of a conducting sphere of radius r with a total charge of q uniformly distributed on its surface is

  1. proportional to qr
  2. independent of r
  3. proportional to \frac{q}{r}
  4. independent of q

Answer. d

9. The field strength at a point of finite distance from an infinitely long straight uniformly charged conductor is obtained by considering the radial (R) component and the longitudinal (L) component of the forces acting on a unit charge at the point, by the charges on the elemental length of the conductor. The resultant field strength is

  1. the sum of R-components, when the sum of L-components is zero
  2. the sum of L-components, when the sum of R-components is zero
  3. the sum of both R- and L-components
  4. average of the sums of R- and L- components

Answer. a

10. In practice, Earth is chosen as a place of zero electric potential because it

  1. is non-conducting
  2. is easily available reference
  3. keeps losing and gaining electric charge every day
  4. has almost constant potential

Answer. d

11. Consider the following statements associated with the basic electrostatic properties of ideal conductors:

  1. The resultant field inside is zero.
  2. The net charge density in the interior is zero.
  3. Any net charges reside on the surface
  4. The surface is always equipotential.
  5. The field just outside is zero.

Which of the above statements are correct?

  1. i, ii, iii and iv
  2. iii, iv and v only
  3. i, ii and iii only
  4. ii and iii only

Answer. a

12. The electric field lines and equipotential lines

  1. are parallel to each other
  2. are one and the same
  3. cut each other orthogonally
  4. can be inclined to each other at any angle

Answer. c

13. The electrostatic force of repulsion between two α-particles of charges 4.0 x 10-19 C each, and separated by a distance of 10-10 cm is

(Given εo = 8.854 x 10-12 Nm2/C2)

  1. 57.6 x 10-4 N
  2. 28.8 x 10-4 N
  3. 14.4 x 10-4 N
  4. 3.6 x 10-4 N

Answer. c

14. If E = 0 at all points on a closed surface

  1. The electric flux through the surface is zero.
  2. The total charge enclosed by the surface is zero.
  3. Charge resides on the surface.
  1. i and ii only
  2. i and iii only
  3. ii and iii only
  4. i, ii and iii

Answer. a

15. Two identical coaxial circular loops carry the same current circulating in the same direction. If the loops approached each other, then the current in

  1. each one of them will increase
  2. both of them will remain the same
  3. each one of them will decrease
  4. one will increase while in the other the current will decrease

Answer. a

16. A quantitative relation between induced emf and rate of change of flux linkage is known as

  1. Maxwell’s law
  2. Stoke’s law
  3. Lenz’s law
  4. Faraday’s law

Answer. d

17. The equation of continuity defines the relation between

  1. electric field and magnetic field
  2. electric field and charge density
  3. flux density and charge density
  4. current density and charge density

Answer. d

18. Electric flux through a surface area is the integral of the

  1. normal component of the electric field over the area.
  2. parallel component of the electric field over the area.
  3. normal component of the magnetic field over the area.
  4. parallel component of the magnetic field over the area.

Answer. a

19. The following point charges are located in air:

+0.008 μC at (0, 0) m

+0.05 μC at (3, 0) mn

-0.009 μC at (0, 4) m

The total electric flux over a sphere of 5 m radius with centre (0, 0) is

  1. 0.058 μC
  2. 0.049 μC
  3. 0.029 μC
  4. 0.016 μC

Answer. b

20. Two charges are placed at a distance apart. Now, if a glass slab is inserted between them, then the force between the charges will

  1. reduce to zero
  2. increase
  3. decrease
  4. not change

Answer. c