when a potential difference is induced across a conductor which is experiencing a change in its external magnetic field
when does a conductor experience a change in its external magnetic field
when it passes through magnetic field lines
if the conductor is part of its own complete circuit , the induced p.d. will result in a current in the circuit . If the current produces its own magnetic field too , the magnetic field will oppose the original change in the external magnetic field
two different situations where you get electromagnetic induction:
an electrical conductor and a magnetic field move relative to eachother
the magnetic field through an electrical conductor changes ( gets bigger , smaller or reverses )
generators are the opposite of motors - they use the relative motion of a conductor and a magnetic field to induce a p.d. and a current
generators:
if the direction of motion is reversed , then the direction of the induced p.d. / current reverses too
if the current induced will be greater if there are more turns on the coil , the magnetic flux density is increased or if the speed of rotation is increased
two types of generators:
alternators
dynamos
alternators
some alternators rotate a magnet in a coil of wire
as the magnet spins , an alternating p.d. is induced across the ends of the coil . The p.d. changes direction every half turn because the direction of the field changes as the magnet rotates
this produces an a.c. if the coil is part or a complete circuit
you can also generate a.c. by rotating a coil in a magnetic field
slip rings at the ends of the coil remain in contact with brushes that are connected to the rest of the circuit . This means the contacts don’t swap every half turn , so they also produce a.c.
dynamos generate direct current
rotate a coil in a magneticfield
the output p.d. and current change direction with every half rotation of the coil , producing a.c. . The coil is part of a completecircuit
a split-ringcommutatorswaps the connection every half turn to keep the current flowing in the same direction - so it changes a.c. to d.c.
microphones work due to electromagnetic induction
a dynamic microphones structure is like a loudspeaker , but the cone is replaced by a diaphragm
sound waves cause the diaphragm to move back and forth when hit by them
as the diaphragm moves , the coil of wire moves , inducing a p.d. across the ends of the coil of wire
the coil is part of a circuit , so the induced p.d. means variations in current in the electrical circuit
state what is different about the current produced by alternators and dynamos
an alternator produces a.c. and the dynamo produces d.c.
if a wire cuts through magnetic field lines , potential difference is induced across the ends of the wire . If the wire is part of a complete circuit , a current is induced in the wire
if the wire moves parallel to the field lines , zero p.d. is induced
to increase the size of the current , you could:
move the wire ( or magnet ) faster
increase the magnetic field strength
coil the wire so more wire is in the field
alternator pt.2
rotating coil in a magnetic field
produces alternating p.d. and alternating current
dynamo pt.2
(d.c.) generator
the potential difference that drives a current does not change direction
to increase the voltage of an alternator we can:
use more turns on the coil
use a stronger magnetic field
rotate the coil faster
what would happen if we used an electric motor in reverse?
the split-ring commutator would reverse the current every half turn