magnetism Flashcards
whats a magnetic compass
- tiny magneti needle pivoted at itsz center
- attracted to the earths mag field so one end always points north and the other south
general rule of magets
like poles repel
opposite poles attract
what are magnets made of/what can be magnetised
iron
steel
nickel
cobalt
what are permenet magnets made of and why
steel because it is hard to demagnetise
what is the shape of magnetic field lines
- more concentrated at the more attractive orth and south poles
- curve around
-always curve from north to south
whats a magnetic field and where is it strongest
- region around a maget
- strongest at poles
- distance makes the strength weaker
whats induced magetism
- when an unmagnetised magnet is placed in a magnetic field and magnetism is created
what else does induced mag cause
- attraction between the nearest poles of the newly magnetised material and the bar maget it has become magnetised by
magnetic field near a wire carrying current
- a series of concentric circles
- centered around the wire
- in a plane perpendicular to the wire
corkscrew rule
when the current is straight it travels clockwise as it would be if you were screwing down the wire
opposite for reverse as if you are unscrewing
whats a solenoid
long coil of insulated wire
how does increasing and decreasing the current affect the mag field
- increasing the currnet strengethns
- decreasing reverses the direction of the mag field
mag field in a solenoid
- field lines are parrlel to its axis
- all are in the same direction
uniform mag field
one where all the mag field lines are parralel and the same direction
mag field outside the solenoid
- similar to the circular field of a bar magnet
- each line fully loops around as it passes through the solenoid
whats an electromagnet
solenoid where the insulated wire is wrapped around an iron bar
this is induced magnetism and so the unmagnetised iro is magnetised every time the current is switched on
the motor effect
a force acts on a magnetised wire in another magnetic field when a current passes through it
how can the force in the motor effect be increased
increasing currnet
stregtheing magnet/magnetic field
increasing length of conductor
how does the angle effect the size of force i the motor effect
- perpendicar wire to mag field is a greatest force
- parralel wire to mag field means the force is at zero
when is a mag field produced
when a current moves through a wire
whats magnetic flux density
strentgh of a magnetic field
whats mag flux desnity measured in
teslas
calculation for the size of the force acting on the wire in the motor effect
F = Mag flux density X current x length
flemmings left hsnd rule
thumb = direction of motion
first finger = direction of mag field
second= direction of current
what is magneticallly soft
it means you gain and lose magnetism slowly
How to increase strength of an electromagnet
You could increase the current,
increase the number of turns of wire while keeping the length of the solenoid the same,
reduce the length of the solenoid while keeping the number of turns of wire the same,
or add a soft iron core.
Why is the mag field arohnd a solenoid strong
Mag fields around each turn/coil of a solenoid are lined up closely together
Useful properties of electromagnets
- can be switched on and off
- strength of field can be changed by changing currnet
electric motor issue
-coil of charged current where the force is both down and up depending on the flow of the current
- the differing forces experiences at either side means it means to spin clockwise
- when it turns 180 it will start turning anti clockwise
- this means it wouldnt ever turn 360
how to help e;ectric motor
- change direction of current every 180 turn
- add a split ring commutator which does this through swapping carbon brushes every half turn
- this means that the forces keep acting in the same directuon
