P7: Magnetism And Electromagnetism (triple) Flashcards
Which way do magnetic fields go?
From north to south
What’s the difference between a permanent magnet and an induced magnet?
Permanent magnets produce their own magnetic field.
Induced magnets are materials that turn into magnets when they’re put into a magnetic field.
What is the right hand rule?
When a current flows through a wire a magnetic field is created around it.
The direction of the field is shown when you use your right hand in a thumbs up position. The direction of your fingers curving round is the direction of the field.
What is a solenoid?
A coil of wire.
Describe the magnetic field produced by a solenoid.
Strong and uniform
Outside the coil the field is like that of a bar magnet
The ends of the solenoid act like a north and South Pole
The right hand rule shows the direction of the field.
Force acting on conductor =
Magnetic flux density * current * length
Describe the use of the left hand rule.
ThuMb: Motion
First finger: Field
SeCond finger: Current
Define the generator effect.
the induction of a potential difference in a wire which is experiencing a change in magnetic field.
How do generators work?
spinning a magnet in a coil.
How do you increase the induced potential difference caused by a generator?
increase the rate at which the magnetic field is changing. you can do this by increasing the speed of the movement or increasing the strength of the magnetic field that is being cut.
What is the main difference between a dynamo and an alternator.
alternators have slip rings and bushes so the contacts don’t swap every half turn. dynamos have a split-ring commutator so swap connections every half turn.
How does a loudspeaker use the motor effect?
an alternating current is sent around a coil. this coil surrounds one pole and is surrounded by another. when the current flows through the coil a force ants on the coil, which causes it to move. this causes the cone to vibrate creating sound waves.
How do microphones work?
the sound wave hits a diaphragm connected to a coil. the coil moves in and out creating a current because it surrounds and is surrounded by opposite poles. this current is used to reproduce the same pressure associated with the recorded sound using a speaker.
What is the transformer equation?
(Vp / Vs) = (np / ns)
(input potential difference/out put potential difference) = (number of turns on primary coil/number of turns on secondary coil)
What similarity does the input and output of a transformer have? Why?
they both have the same power. transformers are almost 100% efficient.
