where is the magnetomotive force (mmf), and is the magnetic flux.
In order to calculate the magnetic reluctance, consider a magnetic circuit of length and cross-sectional area , as diagramed in Figure 1.
We know that the magnetic field strength can be written as:
where is the current in the coil, and is the number of turns (for a more detailed discussion on the magnetic field strength see Field Strength ). Furthermore, can be related to the magnetic flux density with the equation:
Example - Magnetic flux and flux density of a toroid
Consider a toroid with the mean length of , the cross section of , and the relative magnetic permeability of . What is the magnetic flux and the magnetic flux density if the coil has 10 turns and the current is 2 amperes ?