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Engineering ToolBox > Inductance
Inductance is the property of a circuit when there is an electro magnetic field - e.m.f. - induced into the circuit by the change of flux linkages produced by a current change.
The unit of inductance is henry - H - where a circuit has an inductance of one henry when an e.m.f. of one volt is induced by a current changing at the rate of one ampere per second.
Induced electromagnetic field - e.m.f. - in a coil can be expressed as
E = -n dΦ / dt (1)
where
E = electromagnetic field - e.m.f. (Volts)
n = turns
dΦ = change in flux (Webers, Wb)
dt = time (s)
Alternatively, induced electromagnetic field - e.m.f. - in a coil of inductance L henrys can be expressed as
E = -L dI / dt (1)
where
L = inductance (henrys, H)
dI = change in current (Amperes)
dt = time (s)
The e.m.f. induced in a coil of 500 turns when there is a change of flux of 30 mWb linking with it in 30 ms can be calculated as
E = -500 30x10-3 (Wb) / 30x10-3 (s)
= -500 Volts