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Electromagnetic induction It is the conversion of mechanical energy to electrical energy
Electromagnetic induction is when an emf is induced in a conductor due to it moving
through a magnetic field
In electromagnetic induction, Flemings right hand rule is used.
When a conductor cuts through magnetic field lines, there is a change in magnetic flux which
causes work to be done which is transformed to electrical energy. When attached to a
complete circuit, a current will be induced
If it is not a part of a complete circuit, negative charge will accumulate at one end of the
conductor leaving the other end positively charged. We have an induced emf across the
ends of the conductor
Electromagnetic induction occurs when
1. A conductor cuts through a magnetic field
2. Direction of magnetic field through a coil change
Experiment 1: moving a magnet through a coil
When a coil is connected to a sensitive voltmeter, a bar magnet can be moved in and out of
the coil to induce an e.m.f
1. When the bar magnet is not moving:
Voltmeter reading = 0
Because rate of change of flux = 0 and no emf is induced
2. When bar magnet starts moving inside the coil:
There is a reading on the voltmeter
As the bar magnet moves, its magnetic field lines ‘cut through’ the coil, generating a
change in magnetic flux
Emf is induced, shown by the voltmeter
3. When the bar magnet starts moving outside the coil:
Magnet changes direction so the direction of induced current changes direction
Emf is induced in the opposite direction which is shown by the voltmeter (shows
opposite sign)
How to increase induced emf:
(a) Moving magnet faster through the coil (induces emf of higher magnitude as rate of
change of flux increases)
(b) Adding more turns to the coil
(c) Increasing strength of the bar magnet
When (for example) a north pole of a bar magnet is being pushed into a coil, the end of the
coil near the bar magnet becomes a north pole and opposes the movement of the magnet
into the coil which means work has to be done to push the magnet into the coil and energy
transferred by your work is transferred to electrical energy of the current
If the bar magnet is replaced with a wire connected to a voltmeter and moved between 2
magnets, step 1,2, and 3 will be the same.
Note that the wires are moved up and down rather than in and out like the bar magnet
How to increase induced emf:
(a) Increase length of wire
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