Define EM induction
A voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it
What is Faraday’s Law?
A changing magnetic field through a circuit induces an EMF. The induced EMF is directly proportional to the rate of change of magnetic flux through the circuit
Difference between generator and motor effect
Generator - Force on coil -> causes current
Motor - current in coil -> causes a force on coil
What is right hand rule used for
Generator effect
What is left hand rule used for
Motor effect
What is right hand grip rule for?
Currents in wires causing magnetic fields
What causes the generator effect?
Relative motion between a conductor and a magnetic field induces an EMF due to electromagnetic induction
Factors affecting size of induced potential difference
Speed of movement
number of turns
size of coil
strength of magnetic field
What determines direction of induced potential difference
Orientation of magnet poles
direction of movement
What does a generator produce?
Alternating current (a.c.)
What does a dynamo produce?
Direct current (d.c.)
How does an alternator work?
Rotating coil in magnetic field connected to slip rings and brushes. Coil cuts field lines inducing alternating potential difference and alternating current
Why does an alternator produce a.c.?
Because the coil changes direction relative to the magnetic field every half turn so induced voltage reverses
How does a dynamo work?
Rotating coil in magnetic field connected to split-ring commutator. Coil cuts field lines inducing potential difference
Why does a dynamo produce d.c.?
Split-ring commutator reverses connections every half turn so current always flows in same direction
What is the key difference between alternator and dynamo?
Alternator uses slip rings and produces a.c. Dynamo uses split-ring commutator and produces d.c.
What causes induced current in generators and dynamos?
Relative motion between coil and magnetic field cutting field lines
Describe how a generator generates electricity
A coil of wire rotates in a magnetic field. The coil cuts through magnetic field lines. This induces a potential difference across the coil. If the coil is part of a complete circuit an alternating current flows. Slip rings and brushes maintain electrical contact while the coil spins
What is a transformer?
A device that changes the size of an alternating potential difference or current
What does a transformer consist of?
Primary coil secondary coil iron core
Why is iron used in a transformer?
It is easily magnetised
How does a transformer work?
AC in primary coil creates changing magnetic field. Iron core carries field to secondary coil. Changing field induces alternating potential difference in secondary coil
Why must transformers use AC?
AC produces a changing magnetic field needed for induction
What does a step-up transformer do?
Increases voltage has more turns on secondary coil than primary
