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P7 - Magnetism and electromagnetism - Coggle Diagram
P7 - Magnetism and electromagnetism
Electromagnets :
when a current flows in a waire, it creates a
circular magnetic field
around the wire
this can
deflect
the needle of the magnetic compass
the strenth of the magnetic field is greater
closer the wire
if current is increased
solenoids
consists of a wire coiled up into a
spiral shape
when an electric current flows, the shape of the magnetic field is very similar to the field of a bar magnet
field is strong and uniform
small magentic field caused by the current in
each coil
add together to make a stronger magnetic field
it is a solenoid with an iron core
iron core
increases
the magnetic field stegth
simple electromagnet is amde by coiling a wire around a iron nail
--> electric bells and door locks
motor effect
a wire carrying a current creates a
magneitc field
that interacts with another magnietic field, causing a force that pushes the wire at
right angles
Force = magnetic flux density x current x length
F = BIL
N = T x A x m
Flemings left hand rule
Forefinger = field
perpendicular
north to south
second finger = current
from
positive
to
negative
Thumb = movement
direction which the force acts
Electric motors
a coil of wire carrying a current in a magnetic field will experance a force that makes it
rotate
the rotations makes an electric motor
simple motor has a direct current as coil roated in one direction
positive or negative
current on left hand part of coil causes a
downwards force
and the current in right hand part causes an
upwards force
coil rotated
anticlockwise
because of the downwards and upwards force
when a coil is
vertical
, it moves
parallel
to the magnetic field, therfore producing
no force
the motor will come to a stop
momentum of motor carries it on round a little
a
split ring communtator
chamges the current direction every half turn
conducting brushes reconnect with the commutator ebery half turn, causing ;
the current to flow in the
opposite direction
through the wire in the coil
each side of the coil is now near the opposite magnetic pole
Loudspeaker and headphones
motor effect is used inside head phones that contain small loudspeakers
variations in an electric current cause variations in the magnetic field produced by an
electromagnet
cone moves which creates pressure variatio in the air, in forms of
sound waves
alternating current creases sound waves by
a current in the coil that creates an
electromagnetic fiel
the electromagnetic field then interacts with the
permanent magnet
generating a force which pushes the cone **outwards
the current is made to flow in the
opposite direction
direction of electromagnetic field reverses
force on cone pulls it back in
repeatedlty alternating the current direction makes the cone
vibreate
in and out
cone vibrations cause pressure variations in the air which are soundwaves
Magnetic fields
Permanent magnet
produce their
own
magnetic field
can
attract and repel
magnetic field
CANNOT
be turned on/off
--> bar magnets and horse shoe
Induced magnets
becomes magnetic when in a
magnetic field
can ONLY
ATTRACT
lose most or all thier magnetism when removed from magnetic field
a magnetic field
is the region around a magnet where a force acts on another magnetic or on a magnetic mateiral
invisible, but cn be detected using a megnetic compass
a compass contains a small bar magnet on a
pivot
so that it can rotate that points in the direction of the Earth's magnetic field
can be mapped out using small
plotting compasses
place the plotting compass neae the magnet on a peice of papaer
mark the direction the campass needle points
move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
out north and in south
closer the lines, the
stronger
the magnetic field
earth's core is made form iron and nickel that produces a magnetic field
magnetic field line
never cross each other
Electromagnetic induction
generator effect
a magnet is moved into a coil of water, causing
electromagnetic induction
induced voltage produces an induced current is the conductor is connected in a complete circuit which creates a magnetic field around itseld
this magneitc field opposes the original change
an induced current increase if:
magnetic field strength increses
number of turns on the coil is increased
the speed of movement increase
ac generator
produced a potential difference
consists of a coil of wire rotating in a magnetic fiels
car uses an alternatore to keep the battery charged to run the electrical system while the engine is working
has slip rings and burshes that constantly contract, making it an alternating current
as one side of the coil moves up through the magnetic field so a potential difference is induced in
one direction
as rotation continues and one side of the coil moves down, the induced p.d. reverses direction, produing an alternating current since it is constantly changed
Transformers