Question

The materials suitable for making electromagnets have:
A. High retentivity and high coercivity
B. Low retentivity and low coercivity
C. High retentivity and low coercivity
D. Low retentivity and high coercivity

Answer 1

Hint: An electromagnet as the name suggests, has a material which as current in the coil around it flows, produces a magnetic field to magnetize it. Try to think about what are the different properties that might be desired in an electromagnet and how do they relate with retentivity and coercivity.

Complete step-by-step answer:
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets have a wire wound into a coil around the material. A current through the wire creates a magnetic field, which generates magnetic behaviour of the material. An ideal electromagnet has the desired properties:
Firstly, the material should be able to store the magnetization for a longer time. Secondly, while magnetizing a material it might reach saturation, therefore the material should have a tendency to come out of saturation on application of an external force or a field.
The retentivity of a material is defined as its capacity to remain magnetized after the external magnetizing field is not being applied. A material with high retentivity will keep some magnetic properties and become a permanent magnet, whereas a material with low retentivity will lose its magnetization.
Coercivity of a ferromagnetic material is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has reached saturation. When the coercive field of a ferromagnet is large, the material is said to be a hard or permanent magnet.
Therefore, option C. high retentivity and low coercivity is the correct answer.

Note: For application in electromagnets it is not desirable that a material becomes a permanent magnet as one must have control over when the material has to be magnetized in electromagnet. While permanent magnets stay magnetic forever therefore, applying an electric current like in the case of electromagnet will have no effect.