Test: Electrostatic Energy & Its Properties - Electrical Engineering (EE) MCQ

Answer: c
Explanation: The energy in an electric field directly magnitude of charges. Thus electric field and flux density are also dependent. But the applied field affects only the polarisation and it is independent of the energy in the field.

Answer: a
Explanation: The energy in an electric field is given by, W = 0.5 x D x E, where D = 6 and E = 4. We get W = 0.5 x 6 x 4 = 12 units.

Answer: a
Explanation: The energy in an electric field is given by, W = 0.5 x D x E. Since D = εE, we get W = 0.5 x ε x E². On substituting the data, we get 3.16 microjoule.

Answer: c
Explanation: Equipotential surface is an imaginary surface in an electric field of a given charge distribution in which all the points on the surface are at the same electric potential.

Answer: a
Explanation: Since the electric potential in the equipotential surface is the same, the work done will be zero.

Answer: a
Explanation: By Stoke’s theorem, when curl of a path becomes zero, then
∫ E.dl = 0. In other words the work done in a closed path will always be zero. Fields having this property is called conservative or lamellar fields.

Answer: a
Explanation: Using potential, we can calculate electric field directly by gradient operation. From E, the flux density D can also be calculated. Thus it is not possible to calculate energy directly from potential.

Answer: c
Explanation: Since superconductors have very good conductivity at low temperatures (σ->∞), they have nearly zero resistivity and exhibit perfect diamagnetism.

Answer: b
Explanation: Debye is the standard unit for measurement of electric dipole moment. 1 Debye = 3.336 x 10^-30 Coulomb-meter.

Answer: c
Explanation: Ceramic materials are generally brittle. Since these materials are used in capacitors, they have higher dielectric constant than polymer. With respect to energy, they possess high electrostatic energy due to very high dielectric constant (W α ε).

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

Answer: c
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.

Answer: a
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.

Answer: c
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.

Answer: c
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.

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

Answer: a
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.

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

Answer: b
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.

Answer: b
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.