This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Permanent Magnets and Electromagnets”.
1. Which one of the following is feebly repelled by a magnet?
a) Diamagnetic materials
b) Paramagnetic materials
c) Ferromagnetic materials
d) Ferrimagetic materials
View Answer
Explanation: Diamagnetic materials are those which when placed in a magnetizing field are feebly magnetized in a direction opposite to that of the magnetizing field. Therefore, it is feebly repelled by a magnet. Example: zinc, gold, etc.
2. Which one of the following, when suspended freely, slowly sets itself parallel to the direction of the magnetic field?
a) Ferromagnetic materials
b) Diamagnetic materials
c) Paramagnetic materials
d) Ferrimagnetic materials
View Answer
Explanation: Paramagnetic materials are those when suspended freely inside the magnetic field, it slowly sets itself parallel to the direction of the magnetic field. When placed in a non-uniform magnetic field, it tends to move from weaker to a stronger magnetic field.
3. Which among the following has a relative permeability much larger than 1?
a) Diamagnetic materials
b) Ferromagnetic materials
c) Paramagnetic materials
d) Ferrimagnetic materials
View Answer
Explanation: The relative permeability of ferromagnetic materials is much larger than 1. Ferromagnetic substances are those, which when placed in a magnetic field are strongly magnetized in the direction of the magnetizing field, i.e., it is strongly attracted by a magnet.
4. Aluminum is a diamagnetic material.
a) True
b) False
View Answer
Explanation: No, aluminum is a paramagnetic material. Paramagnetic materials are those, which when placed in a magnetic field are feebly magnetized in the direction of the magnetizing field, i.e. it is feebly attracted by a magnet.
5. Arrange the following in the increasing order of magnetic susceptibility.
a) Paramagnetic < Diamagnetic < Ferromagnetic
b) Paramagnetic < Ferromagnetic < Diamagnetic
c) Ferromagnetic < Paramagnetic < Diamagnetic
d) Diamagnetic < Paramagnetic < Ferromagnetic
View Answer
Explanation: Diamagnetic materials have a small and negative value of magnetic susceptibility. Paramagnetic materials have a small and positive value of magnetic susceptibility and ferromagnetic materials have a large and positive value of magnetic susceptibility.
6. Identify the expression for Curie’s constant from the following.
a) χm = C × T
b) χm = C × 2T
c) χm = \(\frac {C}{T}\)
d) χm = \(\frac {C}{2T}\)
View Answer
Explanation: Curie’s law in magnetism states that the magnetic susceptibility of paramagnetic materials is inversely proportional to its absolute temperature and it is given by:
χm = \(\frac {C}{T}\)
7. Pick out the temperature at which iron becomes paramagnetic?
a) 800 °C
b) 700 °C
c) 600 °C
d) 500 °C
View Answer
Explanation: Iron is a ferromagnetic material. Ferromagnetism decreases with a rise in temperature, and above a certain temperature called “Curie’s temperature,” ferromagnets become paramagnets. For iron, it is approximately, 800 °C.
8. Soft iron is used in the cores of transformers.
a) True
b) False
View Answer
Explanation: Soft iron has high permeability and low retentivity and is used as an electromagnet. The area under the hysteresis loop for soft iron is less. So where the repeated cycles of magnetization occur, there on using soft iron core, energy losses are less. That is why soft iron is used in cores of transformers, galvanometers, generators, etc.
9. Pick out the material that cannot be used to make permanent magnets.
a) Copper
b) Aluminum
c) Steel
d) Zinc
View Answer
Explanation: Permanent magnets are made up of materials having high retentivity, high coercivity, and high permeability such as steel. Other suitable materials for making permanent magnets are alnico (an alloy of iron, aluminum, nickel, copper, and cobalt), cobalt steel, and ticonal. That leaves zinc as the one that cannot be used to make permanent magnets.
10. Find the true statement.
a) Most of the substances show ferromagnetism
b) The magnetic susceptibility of diamagnetic substances are temperature independent
c) Water is paramagnetic in nature
d) Typical domain size of a ferromagnetic material is 1 nm
View Answer
Explanation: The magnetic susceptibility of diamagnetic materials doesn’t depend upon temperature. This is often because there’s an outsized barrier between the bottom state and therefore the excited states of diamagnetic substances. Hence, it remains constant during the change of temperature. All the other statements are false.
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