MCQ on Dielectrics

A dielectric is an insulating substance or a poor conductor of electric charge. When dielectrics are exposed to an electric field, they produce almost no current because, unlike metals, they do not contain any loosely bound or free electrons that could travel through the material. Electric polarization, on the other hand, occurs. Positive charges in the dielectric are moved minutely in the direction of the field, whereas negative charges are moved minutely in the opposite direction. The electric field inside the dielectric is reduced by this tiny charge separation, or polarization.

1. A dielectric is an insulator but an insulator, on the other hand, is not always a dielectric. Indicate if the answer is True or False.

a) True

b) False

Answer: Correct option will be: (a) True.

Reason: If a material is to be dielectric, it must have an extremely high permittivity. Insulators are a good example of this. A substantial band gap energy is required for a substance to be an insulator. For a dielectric, however, this is not required.

2. What can be done to make a conductor from a dielectric?

a) By compressing it

b) By heating it

c) By doping it

d) By freezing it

Answer: Correct option will be: (b) By heating it.

Reason: An insulator’s free electrons can be promoted from the valence to the conduction band when the temperature rises. The heating procedure gradually transforms it into a conductor. The insulator loses its dielectric characteristic and begins to conduct in this situation, which is known as dielectric breakdown.

3. Which of the mentioned qualities holds true for a dielectric?

a) At high temperatures, they are superconductors

b) They behave like superconductors at low temperatures

c) They will never be superconductors

d) They have a low dielectric breakdown voltage

Answer: Correct option will be: (b) They behave like superconductors at low temperatures.

Reason: Superconductors have diamagnetism and zero resistance, both of which are valid for a dielectric. They can only be found at low temperatures. At low temperatures, a dielectric could become a superconductor with an extremely high dielectric breakdown voltage.

4. A superconductor’s magnetic susceptibility will be:

a) Positive

b) Negative

c) 0

Answer: correct option will be: (b) Negative.

Reason: A superconductor’s magnetic susceptibility will be negative due to complete diamagnetism. The Meissner effect is the name for this phenomenon.

5. Which of the given materials is a good dielectric?

a) Iron

b) Ceramics

c) Plastic

d) Magnesium

Answer: Correct option will be: (b) Ceramics.

6. When the applied voltage is 2kV and the dielectric thickness is 0.05m, the intensity of the electric field is:

a) 50 V/m

b) 40,000 V/m

c) 50,000 V/m

d) 400 kV/m

Answer: Correct option will be: (b) 40,000 V/m.

Calculation: The electric field is calculated by the formula: E=v/t where, v is the applied voltage and t is the thickness of the dielectric. E=20000.05=40,000 V/m.

7. The dielectric strength of ferroelectric materials is mostly determined by the:

a) The material’s hysteresis loop size

b) the presence of magnetic materials nearby

c) the strength of the electric field

d) the frequency of the applied voltage

Answer: Correct option will be: (c) The strength of the electric field.

8. Which sort of molecule has opposite charges that coincide?

a) Polar molecule

b) Non- polar molecule

c) Unipolar molecule

d) Bipolar molecule

Answer: Correct option will be: (b) Non-polar molecule.

Reason: A non-polar molecule is one in which the centers of mass of positive and negative charges clash with one other. They usually have a dipole moment of zero. They are symmetrical in appearance.

9. What is the term for the ratio of polarization to 0 times the electric field?

a) Density of polarization

b) Electrical susceptibility

c) Dielectric strength

d) Dielectric susceptibility

Answer: Correct option will be: (b) Electrical susceptibility.

Reason: The electrical susceptibility of a dielectric is defined as the ratio of polarization to 0 times the electric field. It explains a dielectric’s electrical behavior.

10. When a dielectric is put in an external electric field, what is the name of the induced dipole moment that develops per unit volume?

a) Relative permeability

b) Polarization susceptibility

c) Electrical susceptibility

d) Polarization density

Answer: Correct option will be: (d) Polarization density.

11. A polar dielectric’s molecules have no dipole moment. Indicate if the statement is true or false.

a) True

b) False

Answer: Correct option will be: (b) False.

Reason: A polar dielectric’s molecules have permanent dipole moments. The dipole moments of various molecules are randomly orientated in the lack of an external electric field due to thermal agitation in the material.

12. What causes ionic polarization?

a) Ion splitting

b) Magnetic field passing 

c) Cation and anion displacement 

d) Never occurs

Answer: Correct option will be: (c) Cation and anion displacement.

Reason: In the presence of an electric field, ionic polarization occurs when cations and anions are displaced in opposing directions from their initial positions.

13. Which of the below polarizations occurs rapidly?

a) Electronic polarization

b) ionic polarization

c) space charge polarization

d) orientation polarization

Answer: Correct option will be: (a) Electronic polarization.

Reason: Electronic polarization is extremely fast and completes as soon as a voltage is supplied. Because electrons are extremely light particles.

14. If the capacitance of a parallel plate capacitor is  3μF and the applied voltage is 1000V, the energy stored in the capacitor equals

a) 0.15 J

b) 0.015J

c) 1.5 J

d) 15 J

Answer: Correct option will be: (c) 1.5 J.

Reason: The energy stored in the capacitor will be given by the formula: U=12CV2. Here, C is the capacitance and V is the potential difference.

15. Which of the below is not a dielectric substance but is an insulating material?

a) Ceramic

b) Rubber

c) Air

d) All of the mentioned

Answer: The correct option will be: (b) Rubber.

16. In capacitors, which of the mentioned dielectric materials can be used?

a) Paper

b) Ceramic

c) Air

d) All of the mentioned

Answer: The correct option will be: (d) All of the mentioned.