Test: Permanent Magnets & Electromagnets - JEE MCQ

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.

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.

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.

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.

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.

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: χ_m = C/T

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.

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.

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.

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.