The area within the hysteresis loop is a product of B and H and this area represents the energy per unit volume that must be used per magnetization cycle to move the domains.

## **Hysteresis Loss**

With appropriate constants, the hysteresis loss can be given in watts per unit volume. An empirical relationship developed by Charles P. Steinmetz gives the hysteresis loss as;

${{P}_{h}}={{k}_{h}}fB_{m}^{n}$

Where P_{h} is the watts per unit volume, k_{h} a constant term, f the number of magnetization cycles per second, B_{m} the maximum flux density, and n the Steinmetz constant normally taken as 1.6. It follows that the greater the energy required to magnetize a sample, the greater the energy needed to demagnetize it. Large hysteresis loops are, therefore, required for permanent magnets, because the large hysteresis loop represents a large storage of energy.

**Eddy Current Loss**

A changing magnetic field induces an emf in a conducting material in that field. Such emf, within a magnetic core, create circulating or eddy currents. The eddy currents encounter the electrical resistance of the core producing power loss proportional to I^{2}R losses. Although the eddy current values cannot be determined directly, the power loss has been found to be given by empirically,

${{P}_{e}}={{k}_{e}}{{f}^{2}}B_{m}^{2}$

Where P_{e }is the eddy current loss in watts per unit volume and k_{e} a constant; f and B_{m} are as previously defined. In order to reduce the magnitude of eddy currents and hence reduce the power loss in a core, magnetic cores are constructed by stacking thin laminations as shown in the following figure.

The laminations are insulated from each other by a thin coat of varnish.

In conclusion, the combined hysteresis and eddy current loss are known as the core losses.