electromagnetism Flashcards
how can a magnetic field be detected
by its effect on another magnet or a moving charged particle
magnetic field line drawing
north on left south on right
three lines as curves from north to south on top and same on bottom
draw the lines with arrows pointing north to south
uniform magnetic field
a magnetic field of constant strength
represented by evenly spaced parallel magnetic field lines between the magnet
shape of a magnetic field can be revealed using
iron filings
plotting compass
plotting compass
shows the direction of a magnetic field
soft magnetic field
easily magnetised and demagnetised
example: iron
hard magnetic field
difficult to magnetise and demagnetise
example: steel
if two magnets are in close proximity to each other with two unlike poles together
a uniform magnetic field forms
only three magnetic elements at room temp
iron, nickel and cobalt
iron filling experiment
- magnet
- paper on top
- sprinkle iron filling while tapping paper
- iron will line up according to shape
plotting compass experiment
- paper down
- magnet on top
- plotting compass close to magnet
- where arrow points to magnet you draw a line
magnet field around a current carrying wire
when current flows, convectional current flows in a wire, it gets hot and a magnetic field appears
this happens to even non magnetic materials
the motor effect
- when a current flows in a wire a magnetic field is produced
- this magnetic field interacts with the magnetic field of the permanent magnet
- the wire experiences a force and is pushed out or pulled in
ho can we increase the size of the force extended on the wire
increase the voltage
use a stronger permanent magnet
the speed of movement increases
the number of turns on the coil is increased
how can we change the direction of motion
reverse the direction of the current flow
reverse the direction of the magnetic field
alloys
mixture of two or more metals
destorying magnets
dropping them (vibrates)
heat it up (particles vibrate)
a coil with the alternating current can demagnetise it
the loudspeaker
an ac current is needed for the speaker to function, this will flow through the coil
which produces a magnetic field around the coil that is constantly changing. This will interact with the field of the permanent magnet.
an electric motor
changes electrical energy into kinetic energy/rotational energy/mechanical energy
describe the motor effect and then say, this causes it to rotate
used for things like hairdryers, fans, cars, planes, fridges, microwaves
what is needed to keep the coil rotating in an electric motor
a split ring communicator
to increase the magnitude of an induced current
- increase the rate at which the magnetic field changes
increase the strength of the permament magnet
dynamo
small generator fitted to a bike to provide electricity for ht lights
inside, a permament magnet is rotated in the middle of the coils of wire this produces a magnetic field. this produces a voltage which causes current to flow (ac)
rotating magnet vs coil
split ring not needed
lemmings left hand rule
thumb- force
first finger- field (North to south)
second finger- (current positive to negative)
devices which use the changing electromagnetic force on a coil of fire in a magnetic field to make a cone vibrate
loudspeaker, headphones
sometimes a wire carries a current in a magnetic field but no electromagnetic force acts on it explain why
if the wire/current is parallel to the magnetic field
what is shown by the direction of the arrow in a magnetic field line
the direction in which a free north pole would point
name one application of the effect indicated by the left hand rule
motor
