This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Types of Dielectric Materials”.
1. What are the two types of dielectrics?
a) Ferroelectric and Piezoelectric
b) Polar and Non-polar
c) Active and Non-active
d) Stable and Non-stable
Explanation: Dielectrics can be divided into two types- polar and non-polar. The ones with a dipole moment are polar dielectrics while others are non-polar dielectrics.
2. Which gas is used for insulation?
Explanation: Nitrogen and Sulphur hexafluoride (SF6) are used for insulation. Nitrogen is used as an insulating medium while SF6 is used in in high and medium voltage switchgears and circuit breakers.
3. CO is a polar dielectric.
Explanation: In CO, the atoms are aligned in a symmetric way. But there is a huge difference in the electronegativity of Carbon and oxygen atoms. Thus, it has a net dipole moment and is polar.
4. Dielectrics which show spontaneous polarization are called as _____________
Explanation: The Dielectric materials which exhibit spontaneous polarization, i.e., are polarized even in the absence of an applied electric field and whose polarization is reversible are called ferroelectric materials.
5. What is the relation between εr and χ?
a) εr = χ
b) εr = 1 + χ
c) εr = 1 – χ
d) εr = χ – 1
Explanation: The departure of the dielectric constant from unity, the value for vacuum, is equal to the electric susceptibility. The correct expression is: εr= 1 + χ.
6. If the dipole moment of a water drop is 4 X 10-30 m and radius is 1 mm, what is the polarization of the drop?
a) 5.6 X 10-13 m-2
b) 7.4 X 10-13 m-2
c) 8.4 X 10-13 m-2
d) 9.4 X 10-13 m-2
Explanation: Molecular mass of water = 18 gm
18 gm of water contains 6.023 X 1023 molecules
18/103 m3 of water contains 6.023 X 1026/18 molecules
Volume of water drop = 4π/3 X (10-3)3 m3
No of molecules in the drop, N = 6.023 X 1026 X 4π X 10-9/18 X 3
= 1.4 X 1017 m-3
Polarization, P = Np
= 1.4 X 1017 m-3 X 4 X 10-30m
= 5.6 X 10-13 m-2.
7. A material of thickness 0.5 mm and dielectric constant 2.5 is subjected to 220 V. What will be the polarization produced?
a) 2.78 X 10-6 C/m
b) 3.91 X 10-6 C/m
c) 4.12 X 10-6 C/m
d) 5.84 X 10-6 C/m
Explanation: We know, Polarization, P = εo(εr– 1)E
Here, εr= 2.5
E = V/d
= 220 / 0.5 X 10-3
= 4.4 X 105 Vm
εo = 8.85 X 10-12 C/Vm
Hence, P = 8.85 X 10-12 X (2.5 – 1) X 4.4 X 105 C/m2
= 5.84 X 10-6 C/m.
8. Electrical counterpart of bar magnets are called as ____________
b) Electrical Magnets
Explanation: Electrets are the electrical counterparts of bar magnets. It produces an electric field in the space around it. They are a bar of dipolar solids.
Explanation: The given figure is a dielectric capacitor. The dielectric produces its own electric field which helps in the movement of charge from one plate to the other in the capacitor.
10. Ceramics cannot be _________
Explanation: Ceramics are inorganic and nonmetallic elements such as oxides, nitrides and carbides. Their production involves firing the constituents at high temperatures.
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