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
A
B
Normal
B
= BA
= BA cos q
q
B
Bfield ⊥ plane of coil
The induced e.m.f. is directly proportional to the rate of change of fluxlinkage 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 Bfield...
motion or force F
magnetic field B
induced current I
observer
l
B
v
e = Blv
e = El = Blv.
http://www.walterfendt.de/ph11e/generator_e.htm
Armature coils, R
Back emf, Eb
Driving source, V
MultiplyingbyI, then
I
t
0
Larger load
Zero load
I
0
pointer
eddy currents
softiron core
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 A1 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.
or

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The energy originally stored
in the magnetic field of the coil
is now stored in the electric
field of the capacitor.

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