Engineering Physics Multiple Choice Questions on “Theory of Ferromagnetism”.
1. In which of the following the magnetic moments align themselves parallel to each other?
a) Paramagnetic material
b) Ferromagnetic material
c) Ferrimagnetic material
d) Diamagnetic material
Answer: b
Clarification: In a ferromagnetic material, the number of unpaired electrons is more. Most of these spin magnetic moments point in one direction. Hence even in the absence of an external field, the magnetic moments align themselves parallel to each other and give rise to a magnetic field.
2. Which of the following is a strong magnet?
a) Diamagnetic material
b) Paramagnetic material
c) Antiferromagnetic material
d) Ferromagnetic material
Answer: d
Clarification: The ferromagnetic materials have a permanent dipole moment. So they act as strong magnets.
3. Which of the following exhibits spontaneous magnetisation?
a) Paramagnetic material
b) Ferrimagnetic material
c) Diamagnetic material
d) Ferromagnetic material
Answer: d
Clarification: The ferromagnetic materials exhibit magnetisation even in the absence of an external field. This property is called spontaneous magnetisation. Hence ferromagnets exhibit spontaneous magnetisation.
4. When does a ferromagnetic material become paramagnetic material?
a) At Curie temperature
b) Below Curie temperature
c) Above Curies temperature
d) Never
Answer: c
Clarification: Curie temperature is the temperature at which the magnetic properties of a material change. When the temperature is greater than curie temperature, ferromagnetic material becomes paramagnetic material.
5. Which of the following materials have a permanent magnetic moment?
a) Ferromagnetic material
b) Ferrimagnetic material
c) Diamagnetic material
d) Paramagnetic material
Answer: a
Clarification: In a ferromagnetic material, there will be a large number of unequal electron spins and hence there exists an enormous amount of permanent magnetic moment.
6. In which of the following increases and then decreases?
a) Ferromagnetic material
b) Antiferromagnetic material
c) Paramagnetic material
d) Diamagnetic material
Answer: b
Clarification: The susceptibility is very small and is positive. It is given by, susceptibility = C/(T+θ) for T>TN. Where TN is the Neel temperature.
Initially, the susceptibility increases slightly as the temperature increases and beyond a particular temperature, known as Neel temperature, the susceptibility decreases with temperature.
7. What is the material used in two port device?
a) Ferromagnets
b) Ferrites
c) Antiferromagnets
d) Paramagnets
Answer: b
Clarification: The ferrites have low hysteresis loss and eddy current loss. Hence they are used in two port devices such as gyrator, circulator and isolator.
8. A paramagnetic material had a magnetic field intensity of 104 A/m. If the susceptibility of the material at room temperature is 3.7×10-3, calculate the magnetisation.
a) 37A/m
b) 3.7A/m
c) 370A/m
d) 0
Answer: a
Clarification: Susceptibility = I/H
Intensity of magnetisation I = Susceptibility × H
Intensity of magnetisation = 37A/m.
9. A paramagnetic material had a magnetic field intensity of 104 A/m. If the susceptibility of the material at room temperature is 3.7×10-3, calculate the flux density in the material.
a) 37Wb/m2
b) 3.725Wb/m2
c) 0.012612Wb/m2
d) 0
Answer: c
Clarification: Flux density B = μ0[H+I]
B = 0.012612Wb/m2.
10. A piece of ferric oxide with magnetic field intensity 106 A/m and susceptibility is 1.5 × 10-3. Find the magnetisation of the material.
a) 15A/m
b) 150A/m
c) 1.5A/m
d) 1500A/m