# Basic Electrical Engineering Questions and Answers – Relative Permeability

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Relative Permeability”.

1. What is the unit for relative permeability?
a) H-m
b) H/m
c) H2/m
d) No unit

Explanation: Relative permeability is the ratio of permeability of the material to the permeability of free space. Since it is a ratio, it does not have any units.

2. Which of the following expressions is correct with respect to relative permeability?
a) B = µrµ0/H
b) B = µrµ0H
c) B = µr0H
d) B = µrµ0/H2

Explanation: For a non magnetic material: B=µ0H. Hence for a material having relative permeability µr, B=µrµ0H.

3. A substance whose relative permeability is less than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

Explanation: A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence its relative permeability is less than that of the free space.
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4. A substance whose relative permeability is more than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Both paramagnetic and ferromagnetic

Explanation: Relative permeability=1+Magnetic susceptibility
Since both paramagnetic and ferromagnetic materials have positive susceptibility, their relative permeability is greater than unity i.e. their permeability is more than the permeability of free space.

5. Diamagnetic substances have relative permeability_____________
a) Greater than 1
b) Less than 1
c) Equal to 1
d) Zero

Explanation: A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence it has relative permeability less than 1.
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6. Paramagnetic substances have relative permeability_____________
a) Greater than 1
b) Less than 1
c) Equal to 1
d) Zero

Explanation: A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence it has relative permeability greater than 1.

7. As the temperature increases up to the Curie temperature, the relative susceptibility of ferromagnetic materials?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

Explanation: The susceptibility of ferromagnetic materials increases with the increase in temperature and then it decreases when the temperature goes beyond the Curie temperature.

8. As the temperature increases beyond the Curie temperature, the relative susceptibility of ferromagnetic materials?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

Explanation: The susceptibility of ferromagnetic materials increases with the increase in temperature and then it decreases when the temperature goes beyond the curie temperature.

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