SP12 - Magnetism and the Motor effect

what poles attract and what poles repel?

like poles repel, opposite poles attract

what is a permanent magnet?

it is always magnetic and can turn objects made from magnetic materials into induced magnets

what are 4 magnetic materials?

cobalt, nickel, steel, iron

how are field lines drawn?

from north to south

what is a solenoid

a copper wire wrapped around itself, an induced magnet

what is Fleming's right hand rule?

middle finger : force
index finger: magnetic field (north to south)
thumb: current

what is the generator effect?

when a wire or a magnetic object is moved up and down between two magnets to create a potential difference, generating a current.

what is the motor effect?

a wire carrying current experiencing a force when placed between two magnets - the magnetic field of the wire interacts with the magnetic field between the two magnets and creates a force

when is the force the greatest during the motor effect

when it is perpendicular to the magnetic field of both magnets

what is the equation to work out the force of when a current passing through a magnetic field at aright angle

force in conductor carrying current at right angles to magnetic field {N} = magnetic field strength {N/A m} * current {A} * length {m}

F = B*I*L

what does a split ring commutator do?

changes the direction of the current every half turn to ensure that the force on the coil always moves in the same direction

what is a uniform magnetic field?

field lines that are evenly spaced due to the magnetic force's strength being the same at each point

what is one way to increase the magnetic field of a solenoid?

place a soft iron core in the middle

what is an electromagnet?

a coil of wire with a current flowing through

is a solenoid a electromagnet?

yes

when is the motor effect the greatest?

when the current carrying wire is perpendicular

how are the different ways you can increase the force produced in the motor effect?

~increase the amount of coils
~increase current flow in wire
~increase strength of both permanent magnets

how does an electric motor work?

what is the generator effect?

a loose wire moved up and down in a magnetic field would create a potential difference, but a closed circuit would then generate a current. a closed circuit wire rotates inside a magnetic field and this creates an alternating current - an alternator

how would you increase the potential difference

~increasing conductor's moving speed
~increase strength of magnetic field
~increase number of coils in wire

alternating current:

slip rings enables current to change direction constantly as both to make an alternator

direct current :

a commutator that enables current to flow in one direction

how does a loudspeaker work?

~electric impulse received which then converts it to a sound wave
~ electric impulse goes into a coil in the loudspeaker, producing a magnetic field in the coil
~this interacts with the magnetic field at the permanent magnet
~force created will cause cone to move
~the vibrations will cause the cone to vibrate as well, moving the air particles and creating sound waves

does an AC generator produce a p.d in one direction or both directions?

both

does an DC generator produce a p.d in one direction or both directions?

only on direction

how does a microphone work?

~cone vibrates when sound waves hit it
~causes coil to move, and it moves relative to the magnetic field thus generating a p.d
~as the microphone is part of a circuit, and induced current flows

how does a transformer work?

~two coils wrapped around an iron core, iron as it is easily magnetised
~the primary coil 1st and secondary coil 2nd
~alternating current flows primary coil which and its magnetic field interacts with the iron core
~the magnetic field changes constantly as the AC current used
~the changing magnetic field creates an alternating current in the secondary

how does a step up transformer work?

increases voltage in the secondary coil -> more coils in the secondary coil

what are step up transformers used for?

used to lower voltage, increasing current flow, placed near homes and schools

how does a step down transformer work?

decreases voltage in the secondary coil -> fewer coils in the secondary coil

what are step down transformers used for?

increase voltage, reduces amount of heat produced in the wires, reducing wasted energy

p = iv

power = p.d * v

vp/vs = np/ns

pd on primary coil/ pd on secondary coil = no of turns in primary coil/no of turns in secondary coil

Vp * Ip = Vs * Is

pd across primary coil * current in primary coil = pd across secondary coil * current in secondary coil