# Electromagnetic Theory Questions and Answers – Electrostatic Properties

This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Electrostatic Properties”.

1. The permittivity is also called
a) Electrostatic energy
b) Dielectric constant
c) Dipole moment
d) Susceptibility

Explanation: The term permittivity or dielectric constant is the measurement of electrostatic energy stored within it and therefore depends on the material.

2. Dielectric constant will be high in
a) Conductors
b) Semiconductors
c) Insulators
d) Superconductors

Explanation: Materials that have very less conductivity like ceramics, plastics have higher dielectric constants. Due to their low conductivity, the dielectric materials are said to be good insulators.

3. Under the influence of electric field, the dielectric materials will get charged instantaneously. State True/False.
a) True
b) False

Explanation: The dielectrics have the ability of storing energy easily when an electric field is applied as their permittivity is relatively higher than any other materials.

4. Insulators perform which of the following functions?
a) Conduction
b) Convection
c) Provide electrical insulation
d) Allows current leakage at interfaces

Explanation: Insulators is a non-conducting material which prevents the leakage of electric current in unwanted directions. Thus it is used to provide electrical insulation.

5. Which of the following properties distinguish a material as conductor, insulator and semiconductor?
a) Free electron charges
b) Fermi level after doping
c) Energy band gap
d) Electron density

Explanation: The only parameter that classifies the material as conductor or insulator or semiconductor is the band gap energy. It is the energy required to make the electrons conduct. This is low of conductors, average for semiconductors and very high for insulators. This means it requires very high energy to make an insulator conduct.
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6. Semiconductors possess which type of bonding?
a) Metallic
b) Covalent
c) Ionic
d) Magnetic

Explanation: Conductors exhibit metallic bonding. Insulators exhibit ionic bonding and semiconductors exhibit covalent bonding due to sharing of atoms.

7. Find the susceptibility of a material whose dielectric constant is 2.26.
a) 1.26
b) 3.26
c) 5.1
d) 1

Explanation: Electric susceptibility is the measure of ability of the material to get polarised. It is given by, χe = εr – 1.Thus we get 1.26.

8. The bound charge density and free charge density are 12 and 6 units respectively. Calculate the susceptibility.
a) 1
b) 0
c) 2
d) 72

Explanation: The electric susceptibility is given by, χe = Bound free density/Free charge density. χe = 12/6 = 2. It has no unit.

9. The susceptibility of free space is
a) 1
b) 0
c) 2
d) ∞

Explanation: For free space/air, the relative permittivity is unity i.e, εr = 1. Thus χe = εr – 1 = 0. The susceptibility will become zero in air.

10. When the electric field becomes zero, which of the following relations hold good?
a) E = P
b) D = P
c) B = P
d) H = P

Explanation: The electric flux density of a field is the sum of εE and polarisation P. It gives D = εE + P. When electric field becomes zero, it is clear that D = P.

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