Definition of Inductance – Voltage induced in a circuit is given by
where ψ represents the flux linkages of the circuit in weber-turns (Wb-T). This can be written in the form
where L=dψ/di is defined as the inductance of the circuit in henrys, which in di
general may be a function of i. In a linear magnetic circuit, i.e., a circuit with constant permeability, flux linkages vary linearly with current such that the inductance is constant given by
If the current is alternating, the above equation can be written as
where λ and I are the rms values of flux linkages and current respectively. These are of course in phase.
Replacing d/dt in Eq. (2.1) by jω, we get the steady state AC voltage drop due to alternating flux linkages as
The Voltage drop in circuit 1 due to current in circuit 2 is
The concept of mutual inductance is required while considering the coupling between parallel lines and the influence of power lines on telephone lines.