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Relation between magnetisation and magnetic field

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I am not getting any idea how to solve it .

asked Mar 26, 2017 in Physics Problems by koolman (4,236 points)
edited May 10, 2018 by sammy gerbil

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The key to answering this question is the Hysteresis Curve (below) which shows how the applied magnetizing force H is related to the magnetization M produced, as measured by flux density B in the sample.

The significant features of the curve are :
(1) saturation - the magnetization cannot increase above the limit at which its magnetic domains are completely aligned with the external field), and
(2) retentivity or remanence - when the applied field is switched off the material remains magnetized.

Assuming the sample is initially unmagnetised (t=0), the magnetization M increases with H, initially in proportion to it but gradually becoming saturated (O to a). As H is reduced to zero (t=4) some magnetization M remains (a to b). As H is increased in the reverse direction there is a steep fall in M until it becomes saturated again at the other extreme (b to c to d). Finally as H is reduced to zero (t=8) M decreases but the material retains some magnetism in the reverse direction (d to e).

These changes correspond to graph # 2.

Although graph # 1 shows saturation it shows no retentivity / remanence - ie when H returns to 0 then M also returns to zero. This is typical of paramagnetic materials. In contrast, iron is ferromagnetic and retains some of its induced magnetism.

Graph # 3 also shows some saturation and no retentivity. However in this case the magnetization is in the opposite direction to the applied field. Such materials are diamagnetic.

Graph # 4 is not typical of any type of magnetic material.

answered May 17, 2018 by sammy gerbil (27,556 points)
selected May 17, 2018 by koolman