P15 - electromagnetism Flashcards
what metals can be magnetised
iron, cobalt, nickel
what are magnetic field lines
lines from north to south of a magnet never cross
what is the difference between a temporary and induced magnet
permanent are always magnetic, induced are magnetic when in a magnetic field
what is the magnetic field around a wire, and how do you find it
concentric circles, right hand rule, thumb points current, fingers point direction of field
what is a solenoid
a wire coiled around a metal bar
what is an electromagnet
a magnet that uses a solenoid to be able to be turned on and off
what happens in a circuit breaker
when current gets too high, the electromagnet attracts a metal plate towards it which opens the circuit stopping it
what happens in a relay (electromagnetism)
when current gets high, the electromagnet attracts a metal plate towards it which closes a different circuit, turning it on ( to turn on a high voltage circuit with a low voltage one)
what is the motor effect
If you put a wire in a magnetic field it will have a force exerted on it - FBI left hand thing
equation for force from motor effect
F = BIL
how does a DC motor work (dynamo)
split ring commutator, as current flows through one side it is lifted by motor effect and other side is lowered, then when rings switch the direction of current switches so the wire spins
what is the generator effect
when you move a magnet through a wire coil, it generates a current
how does an AC motor work (alternator)
same as DC, but with 2 slip rings, each attached to one side of the current so because it constantly switches anyway you don’t need to switch sides
how does a moving coil microphone work
sound waves make diaphragm vibrate which moves a magnet in and out of a coil causing a current alternating at the same frequency as the sound wave
how does a transformer work
where an iron core loop has a primary coil and a secondary coil on it. if the number of turns on the primary coil is larger, it is a step down transformer
