B-H Characteristics :  A magnetic material is identified and characterized by its B – H characteristic. In free space or in air the relationship between the two is linear and the constant of proportionality is the permeability μ0. If B is plotted against H, it will be straight a line. However, for most of the materials the relationship is not linear and is as shown in figure (A). A brief outline for experimental determination of B-H characteristic of a given material is given now. First of all a sample magnetic circuit (with the given material) is fabricated with known dimensions and number of turns. Make a circuit arrangement such as shown in Figure 21.8, to increase the current from 0 to some safe maximum value. Apart from ammeter reading one should record the amount of flux produced in the core by using a flux meter-let us not bother how this meter works.

Now corresponding to this current, calculate H=NI/l and B=φ/a and tabulate them. Thus we have several pair of H & B values for different values of currents. Now by choosing H to be the x axis B to be the y axis and plotting the above values one gets a typical B-H curve as shown in Figure (A)below.

fig...(A)