Field Generation Basic Principles

Magnetic field generation for electric motors when the magnetic flux is generated by a field coil rather than a permanent field magnet is given by the Magnetic Ohm’s law:

$$\varphi =\frac{\text{MMF}}{\mathcal{R}}$$

where $\text{MMF}=NI$, $\mathcal{R}=\frac{g}{A{\mu }_0}$. $\mathcal{R}$ is magnetic reluctance. $\varphi$ is the magnetic flux (conceptually analogous to current).

Magnetic field strength is given by

$$B=\frac{\varphi }{A}=\frac{{\mu }_{0}NI}{g}$$

The unit for $B$ is Tesla.

Thus, we can see that the generated electromagnetic field is directly proportional the current flowing through the coil. As current increases, the magnetic flux density also increases, resulting in a stronger magnetic field.