Question

Define coercivity and Retentivity.

Answer 1

In physics, both terms Coercivity and retentivity are used in magnetism. Coercivity is also known as coercive force or coercive field and Retentivity means the ability to resist any particular force or field but in magnetism it’s used for resisting magnetic field strength.

Complete answer:
Let us first understand coercivity in brief. Coercivity is a measurement of a ferromagnetic substance's ability to withstand an external magnetic field without getting demagnetized. The units in which coercivity is measured is ampere per meter and denoted as overset. It’s also known as coercive force or coercive field.

Retentivity is the ability of a material to resist or to retain magnetic field and it’s measured by the total strength of a magnetic field that is left in a material when an inducing field is removed from the material. The units in which retentivity of a material is measured is weber per square meter or $Weber\,{m^{ - 2}}$.

In the $BH$ curve of the hysteresis loop of a material then the point at which the magnitude of $H$ is zero and $B$ on the Y-axis then, this point on $B$ is called the retentivity of a material. Similarly, In $BH$ curve of the hysteresis loop, point on the negative X-axis where the magnitude of B is zero and have some defined value on $H$, this value of $H$ is called coercivity of a material.

Note: A hysteresis loop is one which represents the variation of B (the induced magnetic flux density) and H (magnetizing force) and it’s generally a closed loop.Electromagnets have high retentivity but low coercivity and for so Iron has high retentivity and low coercivity that’s why it’s used to make electromagnets.