﻿ Magnetic Hysteresis and B H Curve Explanation | apni Physics Physical Science Experiments-Physics Notes & Quiz|apniPhysics

# Introduction of Magnetic Hysteresis Loop

To understand this topic first of all we have to understand the basic concept. Like what is magnetic flux density and magnetic field intensity right? Also, permeability plays an important role in magnetism. Here, two things are by which I can explain the magnetic field density and intensity. One is the permanent magnet and second is the electromagnet.

Magnetic flux density is the amount of magnetic field lines or lines of forces within a given area. These lines of forces can be produced by permanent magnet (like bar magnet, etc.) and electromagnets (like electromagnetic coils). It is denoted by B and measure in units of the Gauss or Tesla.

## Hysteresis Loss Concept and Derivation

Now, in case of a bar magnet the magnetism remain constant you cannot vary it manually except to add some more magnets manually. Here point is about the magnetic field intensity. To understand it feel like you are facing a bulb light when you are close to it its intensity is more while you go away its intensity decreases, right. So in the same sense we have to consider the magnetic field intensity.

In permanent magnets, when I add other permanent magnets manually its magnetic intensity increases. Similarly, in an electromagnet if you will increase the number of turns in the coil or will increase the current in the coil the magnetic field intensity will increase. The magnetic field intensity is denoted by H and its unit is Ampere per meter.

You may have seen the relation between relative permeability and the susceptibility. What it indicates? This shows that relative permeability which is the ratio of the absolute permeability of the material medium and the permeability of free space, changes. It varies with the magnetic susceptibility which further is the ratio of magnetization (M) to the external magnetic field strength (H). It’s mean, if susceptibility varies relative permeability changes. Also susceptibility changes by varying the strength of external magnetic field H.

## B H Curve Concept Solution

So you can say that relative permeability is a function of external magnetic field strength. It will increase if the susceptibility increases. Also, on the other hand you can say that if you have the value of susceptibility you can determine the relative permeability. This is further, helpful to determine the absolute permeability (which is a product of relative permeability to the free space permeability).

As you know susceptibility for the ferromagnetic materials is strongly positive, so the high value of relative permeability (one plus susceptibility) means possibility of high magnetic flux density inside the material comparative to the free space.

Here, you observe that permeability of the material is not constant. Because of this reason B and H relationship is not linear, as we see in the formula (B equal to mu H). For a given ferromagnetic material when you plot a graph between the B and H, you obtain the hysteresis curve or in general if I say, B-H curve.

Here, now I am not going in to the details of various terminology used in to the B-H Curve explanation. Like the retaintivity and coercivity, magnetic saturation, etc. Because enough definitions are available for that and you will not face any problem to understand the definition. But what happens at that time its visualization is important, that I have explained into the video. I hope it will be helpful to you, but still if you face any difficulty just let me know through the comment box.

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#### Dr Sushil Kumar

Dr. Sushil Kumar, a physicist, an eminent researcher and a teacher for the benefit of students and fellow physicists alike. Vyom Hans is an effort to create a better platform and also to help the students to be able to have content at their hands whenever they want, online. Dr. Sushil continues to upload his lectures and post articles about latest researches in physics, academic, physics education, and also lessons about daily life and how physics define every aspect of our everyday movement and life.
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