This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Magnetic Materials”.
1. The presence of parallel alignment of magnetic dipole moment is given by which materials?
a) Diamagnetic
b) Ferromagnetic
c) Paramagnetic
d) Ferromagnetic
View Answer
Explanation: The ferromagnetic materials are characterized by parallel alignment of magnetic dipole moments. Their susceptibility is very large.
2. The magnetic materials follow which law?
a) Faraday’s law
b) Ampere law
c) Lenz law
d) Curie Weiss law
View Answer
Explanation: Generally, the ferromagnetic, paramagnetic and diamagnetic materials follow the Curie Weiss law, which relates the magnetization and the applied field.
3. Find the internal field when the applied field is 12 units, molecular field constant is 0.1 units and the magnetization is 74 units.
a) 86
b) 62
c) 752
d) 19.4
View Answer
Explanation: From Curie law, the internal field of a magnetic material is given by H = Ho + χ M, where χ is the molecular field constant. Put χ = 0.1, M = 74 and Ho = 12, we get H = 12 + (0.1)74 = 19.4 units.
4. In which materials the magnetic anisotropy is followed?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Ferromagnetic
View Answer
Explanation: In materials like iron, the magnetic properties depend on the direction in which they are measured. This is magnetic anisotropy. The material iron is a ferromagnetic material type.
5. Piezoelectric effect is analogous to which phenomenon?
a) Electrostriction
b) Magnetostriction
c) Anisotropy
d) Magnetization
View Answer
Explanation: The piezoelectric effect is the mechanical strain caused on a material like quartz when subjected to an electric field. The same is observed in a ferromagnetic material called magnetostriction.
6. The converse of magnetostriction is called the
a) Magnetization
b) Magnetic anisotropy
c) Villari effect
d) Curie effect
View Answer
Explanation: When a strain is applied, the change in magnetic field is observed. This is the converse of the magnetostriction phenomenon and is called Villari effect.
7. The materials having very small susceptibility at all temperatures are
a) Antiferromagnetic
b) Diamagnetic
c) Ferromagnetic
d) Paramagnetic
View Answer
Explanation: In antiferromagnetic materials, the susceptibility will decrease with increase in temperature. They have relatively small susceptibility at all temperatures.
8. Find the susceptibility when the curie constant is 0.2 and the difference in critical temperature and paramagnetic curie temperature is 0.01.
a) 2
b) 20
c) 0.02
d) 200
View Answer
Explanation: The susceptibility in magnetic materials is given by χm = C/(T-θ), where C is the curie constant, T is the critical temperature and θ is the paramagnetic curie temperature. Put C = 0.2 and T-θ = 0.01, thus we get susceptibility as 0.2/0.01 = 20.
9. The susceptibility is independent of temperature in which material?
a) Paramagnetic
b) Ferromagnetic
c) Diamagnetic
d) Ferromagnetic
View Answer
Explanation: In the diamagnetic materials, the susceptibility is very small and negative. Thus the susceptibility will be independent of the temperature. The atoms of solids having closed shells and metals like gold have this property.
10. In ferromagnetic materials the susceptibility is infinity. State True/False
a) True
b) False
View Answer
Explanation: The ferromagnetic materials are iron, nickel, cobalt which are highly attracted by magnetic field. Thus their susceptibility is also very high and nearing infinity. Also ferrimagnetics have infinite susceptibility.
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