This set of Electromagnetic Theory test focuses on “Dielectric Strength and Constant”.
1. Which of the following is not an example of elemental solid dielectric?
Explanation: Elemental solid dielectrics are the materials consisting of single type of atoms. Such materials have neither ions nor permanent dipoles and possess only electronic polarisation. Its examples are diamond, sulphur and germanium.
2. Ionic non polar solid dielectrics contain more than one type of atoms but no permanent dipoles. State True/False
Explanation: In ionic crystals, the total polarisation is electronic and ionic in nature. Thus, it implies that it contains more than one type of atom and no permanent dipoles.
3. Compute the refractive index when the dielectric constant is 256 in air.
Explanation: By Maxwell relation, εr = n2, where εro is the dielectric constant at optical frequencies and n is the refractive index.For the given dielectric constant we get n = 16.
4. Dielectric property impacts the behaviour of a material in the presence of electric field. State True/False.
Explanation: Based on the dielectric property, a material can be classified as piezoelectric, ferroelectric, pyroelectric and anti-ferroelectric materials under the influence of electric field.
5. Curie-Weiss law is applicable to which of the following materials?
Explanation: Curie-Weiss law is given by χe = εr -1 = C/(T-θ), where C is the curie constant and θ is the characteristic temperature which is usually a few degrees higher than the curie temperature for ferromagnetic materials.
6. Curie-Weiss law is used to calculate which one of the following?
c) Electric susceptibility
d) Magnetic susceptibility
Explanation: Curie-Weiss law is given by χe = εr -1. Thus it is used to calculate the electric susceptibility of a material.
7. Calculate the loss tangent when the dielectric constant in AC field is given by 3 + 2j.
Explanation: The AC dielectric constant is given by εr = ε` – jε“, where ε` is the real part of AC dielectric and ε“ is the imaginary part of AC dielectric. The loss tangent is given by tan δ = ε“/ε` = -2/3.
8. When a dielectric loses its dielectric property, the phenomenon is called
a) Dielectric loss
b) Dielectric breakdown
Explanation: Due to various treatments performed on the dielectric, in order to make it conduct, the dielectric reaches a state, where it loses its dielectric property and starts to conduct. This phenomenon is called as dielectric breakdown.
9. Choose the best definition of dielectric loss.
a) Absorption of electric energy by dielectric in an AC field
b) Dissipation of electric energy by dielectric in a static field
c) Dissipation of heat by dielectric
d) Product of loss tangent and relative permittivity
Explanation: In the scenario of an AC field, the absorption of electrical energy by a dielectric material is called as dielectric loss. This will result in dissipation of energy in the form of heat.
10. Compute the loss factor when the loss tangent is 0.88 and the real part of dielectric is 24.
Explanation: The loss factor is nothing but the imaginary part of AC dielectric. It is given by, ε“ = ε` tan δ. We get loss factor as 24 x 0.88 = 21.12.
Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
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