Viva Questions on Dielectrics
Viva Questions on Dielectrics, Dielectrics Viva Questions, Engineering Physics Viva Questions, Viva Questions on Polarization,
Questions with Answers
Q.1. what are dielectrics?
Ans. Dielectrics are the materials used for charge storage, by polarisation of the molecules. They are also called active dielectrics. The dielectric material increases the capacitance or charge storage ability of a capacitor.
Q.2. Mention a few properties of dielectric materials.
Ans. The properties of dielectrics materials are –
- They are non-metallic materials.
- They have high specific resistance.
- They have a negative temperature co-efficient of resistance.
Q.3. Mention the types of polarisation mechanisms in a dielectric material.
Ans. There are four different types of polarisation mechanisms in the dielectric material.
- Electronic polarisation.
- Ionic polarisation.
- Orientation polarisation.
- Space charge polarisation.
Q.4. Define polarisation.
Ans. Polarisation is defined as the process of creating or inducing dipoles in a dielectric material by an external electric field.
Q.5. Define polarisability.
Ans. Polarisability is the ability of an atom or a molecule to become polarised in the presence of an electric field.
Q.6. Explain electronic polarization.
Ans. Electronic polarization is the displacement of the positively charged nucleus and the negatively charged electron cloud in opposite directions within a dielectric material when an external electric field is applied to it.
Q.7. Explain ionic polarization.
Ans. When ionic solids are subjected to an external electric field the adjacent ions of opposite sign undergo displacement. The relative displacement of charged ions in an external field is called ionic polarization. This type of polarisation occurs only in ionic crystals.
Q.8. Explain orientation polarization.
Ans. Orientation polarisation is a process of reorientation of diploes along the direction of the applied field. This type of polarisation occurs in polar molecules, which possess permanent dipole moments.
Q.9. Explain space charge polarisation.
Ans. When a multiphase dielectric material is subjected to an external electric field, especially at high temperatures, the charges get accumulated at the interface or at the electrodes, thereby inducing dipoles. This process of inducing dipoles in a multiphase dielectric material is called space charge polarisation.
Q.10. Define local field.
Ans. It is the total electric field acting at an atom of a solid or liquid dielectric when subjected to an external electric field. It is the result of the applied field and the field due to the surrounding dipoles.
Q.11. What is Clausius-Mossotti equation? Give the expression.
Ans. The equation which relates the microscopic quantity αe to the macroscopic quantity εr is called the Clausius-Mossotti equation. Its expression is:
Q.12. Define dielectric breakdown.
Ans. Whenever the external voltage applied to a dielectric material exceeds a critical value, a large amount of current flows through it, thereby losing its insulating property. This failure of dielectric as an insulating material is called the dielectric breakdown.
Q.13. Mention a few dielectric materials used in capacitors and transformers.
Ans. Transformer oil, cable oil, cotton tape, press paper, and sulfur hexafluoride.
Q.14. What is the role of dielectric material in capacitors and transformers?
Ans. The major role of dielectric material in capacitors is to store electrical energy and in transformers, they act as insulators and also as a cooling agent.