Electromagnetic Induction. emf is induced in a conductor placed in a magnetic field whenever there is a change in magnetic field. Faraday’s work. Faraday suggested that an e.m.f. is induced in a conductor when 1. there is a change in the number of lines ‘linking’ it ,
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1. there is a change in the number of lines ‘linking’ it,
2. it ‘cuts’ across field lines.
x x x x x x x x x x x x x x x x x x x x x x x x x x x x
= BA cos q
B-field ⊥ plane of coilMagnetic flux
The induced e.m.f. is directly proportional to the rate of change of flux-linkage or rate of flux cutting.
Induced Ialways flows to oppose the movement which started it.
In both cases, magnet moves against a force.
Work is done during the motion & it is transferred as electrical energy.
For a wire cutting through a B-field...
motion or force F
magnetic field B
induced current I
vCalculation of e.m.f.
e = Blv
e = El = Blv.
0Variation of current with the steady angular speed of the coil in a motor
The magnetic flux linkage in a coil the current flowing through the coil.
Where L is the constant of proportionality for the coil.
L is numerically equal to the flux linkage of a circuit when unit current flows through it.
Unit : Wb A-1 or H (henry)
Lis numerically equal to the emf induced in the circuit
when the current changes at the rate of 1 A in each second.