Physics Questions and Answers – Magnetic Properties of Materials

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Magnetic Properties of Materials”.

1. Identify the expression for magnetic induction from the following.
a) B = μo(H+I)
b) B = μo(H×I)
c) B = μo(H-I)
d) B = μo(\(\frac {H}{I}\))
View Answer

Answer: a
Explanation: Magnetic induction (B) is defined as the number of magnetic lines of induction crossing per unit area normally through the magnetic substance, and is given by:
B = μo(H+I)
The SI unit of magnetic induction is Tesla (T).
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2. Which among the following is true about magnetic susceptibility?
a) It is the ratio of magnetic intensity to intensity of magnetization
b) The SI unit of magnetic susceptibility is Tesla (T)
c) It is the ratio of intensity of magnetization to magnetic intensity
d) It is the ratio of magnetic moment to volume
View Answer

Answer: c
Explanation: Magnetic susceptibility of a magnetic substance is defined as the ratio of the intensity of magnetization (I) to the magnetic intensity (H). The expression is given by:
χm=\(\frac {I}{H}\)
Magnetic susceptibility measures the aptness of a magnetic substance to acquire magnetism. It is a unit less constant of magnetic substance.

3. Pick out the unit of magnetic permeability.
a) TmA
b) \(\frac {Tm}{A}\)
c) \(\frac {T}{mA}\)
d) \(\frac {Am}{T}\)
View Answer

Answer: b
Explanation: Magnetic permeability (μ) of a magnetic substance is defined as the ratio of its magnetic induction (B) to the magnetic intensity (H). The expression for magnetic permeability is given as:
μ=\(\frac {B}{H}\)
Magnetic permeability is the ability of a magnetic substances to permit magnetic field lines to pass through it. The SI unit for this quantity is \(\frac {Tm}{A}\).
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4. Relative magnetic permeability is unit less.
a) True
b) False
View Answer

Answer: a
Explanation: Yes, relative magnetic permeability is a unit less constant of magnetic substance. Relative magnetic permeability (μr) of a magnetic substance is defined as the ratio of its magnetic permeability to the permeability of free space. The expression for it is given as:
μr=\(\frac {μ}{\mu_o}\)

5. The relative permeability of a medium is 0.050. What is its magnetic susceptibility?
a) 500
b) 501
c) 49.9
d) 499
View Answer

Answer: d
Explanation: Given: relative permeability (μr) = 500
Required equation ➔ μr = 1+χm
χm = μr – 1
χm = 500 – 1
χm = 499
Therefore, the value of magnetic susceptibility is 499.
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6. The magnetic susceptibility of a paramagnetic material at -800C is 0.0085, then what is its value at -1800C?
a) 0.015
b) 0.016
c) 0.017
d) 0.018
View Answer

Answer: c
Explanation: Given: χm1 = 0.0085; T1 = -800 C = -80 + 273 = 193 K; T2 = -1800 C = -180 + 273 = 93 K
χm ∝ \(\frac {1}{T}\)
\(\frac {\chi_{m2}}{\chi_{m1}} \, = \, \frac {T_1}{T_2}\)
\(\frac {\chi_{m2}}{0.0085} \, = \, \frac {193}{93}\)
χm2 = \(\frac {193 \, \times \, 0.0085}{93}\)
χm2 = 0.017

7. A material has a permeability of 0.1 H/m when the magnetic intensity is 70 A/m. What will be the magnetic induction inside the material?
a) 7 T
b) 0.7 T
c) 70 T
d) 0.07
View Answer

Answer: a
Explanation: Given: permeability (μo) = 0.1 H/m; Magnetic intensity (H) = 70 A/m
Required equation ➔ Magnetic induction (B) = μo × H
B = 0.1 × 70
B = 7 T
Therefore, the magnetic induction inside the material is 7 T.
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8. Ferromagnetic materials does not show hysteresis.
a) True
b) False
View Answer

Answer: b
Explanation: Ferromagnetic materials do show hysteresis. When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. The phenomenon of hysteresis in ferromagnetic materials is the result of two effects ➔ rotation of magnetization and changes in size or number of magnetic domains.

9. Find the correct combination regarding relative permeability and magnetic susceptibility of a paramagnetic substance.
a) μr > 1, χ < 0
b) μr < 1, χ > 0
c) μr < 1, χ < 0
d) μr > 1, χ > 0
View Answer

Answer: d
Explanation: The correct combination for paramagnetic substances is given as follows:
μr > 1, χ > 0
Paramagnetic materials have a small and positive value of magnetic susceptibility (χ). The relative permeability (μr) of paramagnetic materials is just greater than 1.
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