Magnets & Magnetism Flashcards
what is a magnetic field
a field where magnetic materials experience a force
magnetic poles attraction and replusion
north - north = repulsion
south - south = repulsion
north - south = attraction
what do magentic field lines show
Magnetic field lines provide a visual representation of the magnetic field in a given space through use of arrows to show direction.
They also show the strength of the field through the distance of the lines (closer together = stronger/closer field).
And the shape of the field
how to see magnetic field patterns with iron filings
place a peice of paper ontop of a bar magnet
sprinkle iron filings ontop of the paper
gently tap the paper to allow the iron filings to settle on the field lines
how to see magnetic field lines with a compas
what is induced magnetism
When a magnetic material is placed in a magnetic field, the material can temporarily be turned into a magnet.
why can induced magnitism not produce repulsion
because the induced poles are always in the same order as the first magnet. Hence it is not possible for like poles to be facing each other
how do magnetic domain explain induced magnetism
When the domains are pointing in random direction each little magnetic field cancels out its neighbours and the metals will not be magnetic. When external magnetic field is applied the domains line up and reinforce each other (magnetism has been induced)
what are the 4 magnetic materials
iron
nickel
cobalt
steel
what is magnetically soft and what are the materials which are soft
Magnetically soft materials lose their magnetism (iron/cobalt)
what is magentically hard and what are the materials which are hard
Magnetically hard materials retain their magnetism (steel)
how can you use 2 permanent magnets to produce a uniform magnetic field patter
A uniform field is created when two opposite poles are held close together. Magnetic fields are always directed from North to South.
what do electromagnets consist of
a power supply, coil (solenoid) and a Iron core
describe and draw the magnetic field around a straight wire
the field is made up of concentric circles with the wire in the centre
describe and draw the magnetic field around a flat circular coil
similar to the magnetic field of a bar magnet
there are concentric ellipses of magnetic fiele lines around the coil
describe and draw the magnetic field around a solenoid
strong and uniform
outside the coil the field is just like a bar magnet’s field
the ends of a solenoid act like the north pole and south pole of a bar magnet
how does a force effect charged particles in a wire
it can push electrons along the wire, causing current to flow.
or it can can induce forces that move the wire
what is flemmings left hand rule used for
which way the force acts
describe flemmings left hand rule
First finger - field
seCcond finger - current
thuMb - force/motion
what are 4 factors which will speed up the induced potential difference
The speed at which the wire, coil or magnet is moved
The number of turns on the coils of wire
The size of the coils
The strength of the magnetic field
how does a loudspeaker work
An alternating current is fed into a coil, generating an alternating electromagnetic field.
This produces a magnetic force which is continually changing direction.
The coil is connected to a cone which will vibrate and produce a sound.
what is a simple dc motor
DC motors consist of a coil of wire in betweeen two permanent magnets. Direct current flows through the wire and it experiences a turning effect due to the forces exerted on it in the magnetic field. As the current flows in opposite directions on each side of the coil, the forces on each side are in opposite directions making it turn
what does the permenate magnets in a dc motor do
they create a steady magnetic field
which induces and intereacts with the megnetic field of the current
which induces the coil creating a force and motion
what does the current in the wire do in a simple dc motor
take electrical power through direct current, and convert this energy into mechanical energy causing it to rotate
how does a simple dc motor work
current flows through the coil through the positive terminal and out through the negative terminal producing a magnetic field of clockwise forces (as it is inbetween 2 permenate magnents)
because both sides of the coil produce a different force the wire will rotate clockwise 90 degrees and then rotate again 90 degrees but anticlockwise
this is not practicle so you add a split ring communtator to change the direction of the current every half turn
this process continues and so the simple dc motor will turn 360 degrees
what is electromagnetic induction
the creation of voltage in a wire which is experiencing a change in magnetic field
how is electromagetic induction done
by an electrical conductor movin through a magnetic field
the magnetic field changes through a electrical conductor
how can the size of the magnetic force be increases
increase the turns to the coil
have a stronger external magnetic field
increase the electrical current
what is the motor effect
A current carrying wire creates a magnetic field. it can interact with another magnetic field, causing a force that pushes the wire at right angles
what is a simple AC generator
a simple ac generator converts kinetic energy into alternating current (AC) electricity.
it is based on the principle of electromagnetic induction
by the coil rotating + an interaction with the mgnetic field it induces a current in the coil
how can ac be produces
when a coil rotates in a magnetic field
when a magnet rotates within a coil
what is a split ring cummutator
it swaps the positive and negative connections every half turn
this means the direction of current swaps every half turn causing the forces acting on the coil to always be in the same direction
what is a transformer
changes the size of voltage of an alternating current
it is acheived using the generator effect
what is the structure of a transformer
a primary coil
a secondary coik
an iron core
why is iron used in a transformer
because it is easily magnetised
how does a transformer work
they have 2 coils - primary and secondary along with an iron core
when alternating voltage is applied across the primary coil the magnetically soft iron core magnetises and demagnetises quickly
this induces an alternating voltage in the secondary coil
what is a step up transformer
The size of the voltage INCREASES from the primary to the secondary
there will be more turns in the secondary coil
what is a step down transformer
The size of the voltage DECREASES from the primary to the secondary
there will be more turns on the primary than secondary
what is a step up transformer used for
step up transformers are used for transmission in power lines which recues power loss
what is a step down transformer used for
a step down transformer is used in homes to keep us safe
how can you calculate transformers
priamry voltage/secondary voltage = number of turns on primary/number of turns on secondary
if a transformer is 100% efficient then what is the relation between input and output power
input power = output power
equation for is a transformer is 100%
.
what do transformers only work with
AC electricity
what happens to the current if the voltage rises from the primary to the secondary coil
the current drops
what is the national grid
a system or cables and transformers linking power stations to consumers (houses, buildings and factories)
what is the problem with transporting high current
there is lots of heat becuase of the resistance which means you loose loads of energy
how does the national grid work
increase the voltage in the energy power station by using a step up transformer
wires then transmit the electrivity all around the country
just before it reaches its destination (a certain town) the voltage has to be reduced back down by a step down transformer
