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Transcript
Dielectric Properties
Assignment Question: Module -3
Dielectric Materials Model Questions:
01. What is dielectric material? Mention the uses of dielectric materials.
02. Define the following terms (i) Dielectric Polarization, (ii) Polarisability, (iii) Dielectric
Constant, (iv) Spontaneous polarization, (v) Electric susceptibility.
03. Establish the relation concerning D, E, and P.
04. What do you mean by Macroscopic and Microscopic field? What is Lorentz field?
05. Briefly discuss the polarization phenomenon in dielectric materials.
06. Explain briefly the term electronic, ionic and orientation polarization in dielectric system
under static electric field. Derive Langevin-Debye expression
07. What is relative dielectric constant? Derive the expression for the dielectric susceptibility.
Briefly describe with the help of atomic model the dependence of relative dielectric
constant (ε r) on the electronic polarizability (αe).
08. Is the relative dielectric constant (ε r) depends on the atomic size of dielectric materials?
Explain.
09. What do you mean by orientational polarization? Discuss the temperature dependence of
orientational polarization.
10. Estimate the internal electric field strength with in the atoms of dielectric material, placed
under external static electric field.
11. What is Clausius-Mosotti relation of dielectric constant? Develop the relation for
elemental dielectric systems.
12. Arranged in descending order the relative dielectric constant of following materials :
(a) LiCl (b)
Ge
(c)
Diamond
(d)
Si
13. What should be the effect on relative dielectric constant of ionic solid materials, when
placed under optical radiation.
14. Short note: (a) dielectric strength, (b) dielectric loss, (c) Ferroelectricity, (d)
Piezoelectricity.
15. Give name of 3 each – Ferro and Piezo- electric materials. Also point out their most
important uses in industry.
16. Discuss the frequency effect on dielectric value of material.
17. Discuss the frequency dependence of various contributions to dielectric polarizability.
18. Explain briefly the behavior of electronic polarizability (αe) of dielectric material under
a.c field application.
19. Compare the values of natural angular frequencies in (i) electronic polarization and (ii)
ionic polarization of dielectric material under a.c field application.
20. What do you mean by complex dielectric constant of material?
21. Write down the expressions of following parameters under static and a.c. field application
of dielectric materials : (a) Internal electric field (Ei)
(b) Electric dipole (P)
(c) Relative dielectric constant
22. What is dielectric loss? Define loss-tangent of dielectric.
23. Write down the equivalent circuit of a loss-dielectric capacitor.
24. What is dielectric strength? Compare the same in (a) mica, (b) fused silica (c) porcelain.
Arrange then in ascending order.
25. What should be the nature of relative dielectric constant (ε r) under A.C. field? How it is
related with the dielectric loss in the system?
Prepared by Dr. Rajesh Das, Department of Applied Sciences, HIT-Haldia
Page 1
Dielectric Properties
Assignment Question: Module -3
26.
27.
28.
Unit – IV : Problems on Dielectric Materials
01/CR120
A parallel plate capacitor consists of two plates of area 500 sq.cm separated by
a thin sheet of mica of thickness 0.075 mm. If the Є of mica ~ 6.5, then
calculate the capacitance value.
[Ans. 0.0383 μF]
02/BG162
Esti
3
mate the max. amount of electrostatic energy that can be store in 1 m volume of air. Use
dielectric strength of air ~ 3 x 106 V/m.
[Ans. 39.8 J/m3]
03/S551
A simple parallel plate capacitor is design to store 5 x 10-6 C at a potential of
8000 V. If the separation between the palates is filed by alumina with
thickness ~ 0.30 mm and Єr ~ 9.0, then calculate the area of each plate of the
capacitor.
[Ans.2.35 x 10-3 m2]
Prepared by Dr. Rajesh Das, Department of Applied Sciences, HIT-Haldia
Page 2
Dielectric Properties
Assignment Question: Module -3
A parallel plate capacitors having area ~ 6.45 x 10-4 m2 and plates separation ~
0.002 m is connected with external potential 10 V. If the capacitor dielectric
material has value Єr ~ 6.0, then calculate :
(a) the capacitance value - C,
(b) amount of charge stored- Q
(c) dielectric displacement –D and
(d) the polarization – P.
[Ans.1.71 x 10-11F, 1.71 x 10-10C, 2.66 x 10-7C/m2 and 2.22 x 10-7
C/m2]
05/D58
A charge of Q coulombs is distributed homogeneously over the surface of a
sphere with a radius of R meters. If the sphere is in vacuum, find the following
parameters:
(a) the flux density D
(b) the field strength E
(c) the potential V
as a function of the distance r from the centre of the sphere for 0≤r≤α, assume
V(α) = 0.
[Ans. For r < R, D=0, E=0, V=Q/4π Є0.R Volt, For r>R, D=Q/4π r2
Coulomb/ m2, E=Q/4π Є0 r2 Volt/m, V=Q/4π Є0.r Volt]
04/C629
06/D76
The space (separation ~ 1 m) between plates of a parallel plate capacitor is
filled by gas molecules (with N atoms/ m3) and connected with external
alternating field with frequency ~ ω. Then show that
Ne 2 / m 0
*
(a) the dielectric constant of the gas  r = 1+ 2
 0   2  j 2b / m


Ne 2 / m
(b) the admittance per m2 plate area Y* = j  0  2

0   2  j 2b / m 

where the parameters have their usual meanings.
The optical refractive index and the dielectric constant for water are 1.33 and 8.1
respectively. Determine the percentage of ionic polarisibity.
Prepared by Dr. Rajesh Das, Department of Applied Sciences, HIT-Haldia
Page 3