Topic seven - magnetism and electromagnetism Flashcards Preview

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Flashcards in Topic seven - magnetism and electromagnetism Deck (16):

what is a compass comprised of

it is a bar magnet on a super low resistance pivot, so that it can use the magnetic field of the earth to align itself


what are the two different types of magnet

permanent magnet produce their own magnetic field
induced magnets are simply magnetic material which becomes magnetised when it is brought near the bar magnet


which way around is the magnetic field around a current

it is clockwise (R.H. rule)


what is a coiled piece of wire to increase the magnetic field strength called

a solinoid


what is the rule to find the motor effect

flemming's left hand rule


how do you remember which finger goes where



how can you find the size of the force caused by the motor effect

the magnetic flux density (the strength of the magnetic field)
the current through the conductor
the length of the conductor in the magnetic field


how does an electric motor work

you have a ring through a magnetic field. as the current is flowing in opposite directions in each side, one side is pushed up, and the other is pushed down, causing it to rotate. to keep the motor rotating in the same direction, a split ring commutator is used to swap the contacts every half turn. in order to reverse the rotation, you either swap the poles or revers the current.


how does a loudspeaker work

an AC current is sent through a coil of wire attached to the base of a paper cone. the coil surrounds one pole of the magnet and is surrounded by the other. therefore variations in the current make the cone vibrate and make variations in pressure causing sound waves. the frequency of the sound wave is the same as the frequency of the AC so the sound can be changed.


what is the definition of the generator effect

the induction of a potential difference in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field.


describe how a generator works

as you turn the magnet, the magnetic field through the coil changes which induces a potential difference. after a half turn, the direction of the change reverses and so the p.d. reverses. if the rotation of the magnet is kept the same, the A.C. current is kept at the same frequency as the rotation of the magnet.


which had is the generator effect's fleming rule

FBI on the right hand


what is the difference between alternators and dynamos

alternators use motion to create an alternating current
dynamos use motion to create a direct current.


what is absolutely necessary in a transformer

ac current


how does a transformers work

an alternating current in the primary coil causes an alternating pd which induces an alternating magnetic field which induces an alternating pd in the secondary coil, which causes an AC in the secondary coil but with a different pd and current than the first.


how do you work out the difference between the input pd and the output in a transformer

primary pd / secondary pd = primary coils / secondary coils