Anna University Regulation 2013 Information Technology (IT) PH6251 PHY2 2marks & 16marks for all 5 units are provided below. Download link for IT 2nd SEM PH6251 Engineering Physics 2 Short answers, Question Bank are listed down for students to make perfect utilization and score maximum marks with our study materials.
DIELECTRIC MATERIALS
1. Define dielectric constant?
It is the ratio between the absolute permittivity of the medium (ε) and the permittivity of free space (ε0).
Dielectric constant εr = Absolute permittivity (ε) / Permittivity of free space (ε0)
2. Define polarization of a dielectric material.
The process of the producing electrical dipoles inside the dielectric when external electric field is applied is called polarization in dielectrics.
Induced dipole moment (µ) = αE
E → Applied electrical field
α → Polarizability
3. Name the four polarisation mechanisms.
i. Electronic polarisation.
ii. Ionic polarisation.
iii. Orientational polarisation.
iv. Space- charge polarisation.
4. What is electronic polarisation?
Electronic polarisation occurs due to the displacement of positively charged nucleus an negatively charged electrons when an external electric field is applied and there by dipole moment is created.
5. What is ionic polarisation?
Ionic polarisation occurs due to the displacement of cation and anion when an external electric field is applied and there by dipole moment is created.
6. What is orientation polarisation?
Orientation polarisation occurs due to the polar molecules. When an external electric field is applied positive portion align along field direction and negative portion align along opposite to field direction.
7. What is space- charge polarisation?
Space charge polarisation occurs due to diffusion of ions, when an external electric field is applied.
8. Define dielectric loss and loss tangent.
When a dielectric material is subjected to electric field, the electrical energy is absorbed by the dielectric and certain amount of electrical energy is dissipated in the form of heat energy. This loss of energy in the form of heat is called dielectric loss.
The power loss PL α tanδ , where tanδ is called loss tangent and „δ‟ is called loss angle.
9. Define dielectric breakdown and dielectric strength.
Whenever the electrical field strength applied to a dielectric exceeds a critical value, very large current flows through it. The dielectric loses its insulating property and becomes conducting. This phenomenon is known as dielectric breakdown.
It is the minimum strength of electric field required per unit thickness of the dielectric material to produce dielectric breakdown.
10. Mention the various breakdown mechanisms.
i) Intrinsic breakdown and avalanche breakdown
ii) Thermal breakdown
iii) Chemical and Electro-chemical breakdown
iv) Discharge break down
v) Defect breakdown
11. What is intrinsic breakdown?
When a dielectric is subjected to electric field then the electrons in the valence band acquire sufficient energy and go to conduction band by crossing the energy gap and hence become conducting electrons. Therefore large current flows and is called intrinsic breakdown.
12. What is thermal breakdown?
When an electrical field is applied to a dielectric material, some amount of heat is produced. Due to excess of heat, the temperature inside the dielectric increases and may produce breakdown is called thermal break down.
13. What is chemical and electrochemical breakdown?
Electro chemical breakdown is similar to thermal breakdown. When the temperature of a dielectric material increases, mobility of ions increases and hence dielectrics become conducting. This type of breakdown is called as chemical and electrochemical breakdown.
14. What is discharge break down?
When this type of dielectric is subjected to electric field, the gases present in the material will easily ionize and thus produces large ionization current and is known as discharge breakdown.
15. What is defect breakdown?
Some dielectrics have defects such as cracks, pores, blow holes etc. These vacant position may have moisture which leads to breakdown called as defect breakdown.
16. What are ferro-electric materials?
Give examples. Materials which exhibit electronic polarization even in the absence of the applied electrical field are known as ferro-electric materials. Example. Barium Titanate (BaTiO3) Potassium Dihydrogen Phosphate (KH2PO4)
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