- Consider now a single coil/circuit/loop with N turns. As the current in the loop changes the magnetic field and hence the magnetic flux through the loop changes. This changing "self flux" through Faraday's Law leads to an induced emf in the circuit,

- In the same manner as mutual inductance we define the self inductance of the circuit, L, as follows

so that the induced emf - sometimes called a- is given by"back emf"

This "back emf" always opposes the primary emf (due to Lenz's Law), as shown in the diagram at right.

From above, which can be compared to the similar equation
for capacitance .

- Calculating self inductance proceeds by the same steps
as mutual inductance - Calculate
**B**, calculate magnetic flux, then use the second equation above to determine L.

*Dr. C. L. Davis*

*Physics Department*

*University of Louisville*

*email*: c.l.davis@louisville.edu