Electromagnetism Flashcards
What is a permanent magnet?
A magnet that produces its own magnetic field
What is an induced magnet?
A material that becomes a magnetic when placed in a magnetic field. When it’s removed it quickly loses all its magnetism
Explain how to recognise wether a material is an induced or a permanent magnet
Use a permanent magnet. The material that is a permanent magnet will attract to one side of the permanent magnet but the other side will repel. An induced magnet will always attract to the permanent
What does the strength of the magnetic field depend on
What is the motor effect
When a current carrying wire is placed In a magnetic field it experiences a force
How does a generator work?
When a conducting wire cuts through the magnetic field lines, the magnetic field through it changes. This causes a potential difference to be induced across the ends of the wire. If circuit is completed a current will flow
How do dynamos generate direct current
Dynamos have split ring commutators. This swaps the connection every half turn which produces a direct potential difference and hence a direct current.
How do alternators generate alternating current
Alternators have slip rings and brushes. This ensure the connections stay the same ( they do not swap every half turn). This means the potential difference reverses direction so every half turn the current changes direction.
Do microphones use generator or motor effect
Generator
Do loudspeakers use generator or motor effect
Motor
How does a microphone work
Sound waves hit the diaphragm which cause it to vibrate which makes the coil of wire vibrate. As the coil vibrates, it cuts through the magnetic field lines of the permanent magnet. This induces a potential difference across the ends of the wire and when connected to an external circuit, a current will flow.
How does a loudspeaker work
A coil of wire is attached to the base of a paper cone and is wrapped around a permanent magnet and is connected to an ac supply. This alternating current interacts which the magnetic field causes a force in the coil. Because the coil moves, so does the cone. When the current is reversées the force acts in the opposite direction so the cone moves the other direction.
Why can a commutator spin easily after disconnection
There is no current meaning no magnetic field around the coil of wire. This means there is no force to oppose the movement of the commutator through the magnetic field of the permanent magnets.
