magnets Flashcards
What magnetic poles attract
Unlike
What magnetic poles repel
Like poles
What are the three main magnetic materials
Iron nickel and cobalt
What are uses of magnetic materials
Fridge doors – there is a permanent magnetic strip in your fridge door to keep it closed
Cranes – these use induced electromagnet to attract and move magnetic materials
Doorbells – these use electromagnets which turn on and off rapidly, to repeatedly attract and releasing on which strikes the metal bell to produce a ringing noise
Magnetic separator – these are used in recycling plants to sort metal items
What is the difference between permanent and induced magnets?
Permanent
- Produce their own magnetic field all the time
- magnetically hard materials
Induced
- magnets only produce a magnetic field while they’re in another magnetic field
- When you take away the magnetic field it stops producing a magnetic field
What is a magnetic soft material?
Lose magnetism very quickly i.e. pure iron
What is a magnetically hard material?
Lose magnetism more slowly I.e steel
Describe the shape and direction of the magnetic field around a bar magnet
Lines always go from North to south and they show which way of force would act the north pole at that point in the field
The closer together the lines are the stronger the magnetic field
The further away from a magnet you get the week of the field is
How to plot a compass to show the direction of magnetic fields
Put a magnet on a piece of paper and draw around it
Place the compass on the paper near the magnet. The needle will point in the direction of the field line at this position.
Mark the direction of the compass needle by drawing two dots – one at each end of the needle
Then move the compass that the tail end of the needle was rather tip of the needle was in the previous position . Repeat this several times until you end up with a drawing of one field line around the magnet.
Is the Earth of the coal magnetic due to the behaviour of a magnetic compass?
Compasses always point towards the Earth north Pole this is because the Earth generates its own magnetic field
How can a current create a magnetic field?
When a current flows through a long, straight conductor and field is created around it. The field is made up of concentric circles perpendicular to the wire, with the wire in the centre. Changing the direction of the current changes the direction of the magnetic field – use the right hand thumb rule to work out which way it goes.
The large of the current through the wire, or the closer to the wire you are the stronger the field is
What does strength of the field depend on
Size of current and distance from the long straight conductor
How does the current in a magnetic field experience a force?
To experience the full force, the wire has to be at a 90° angle to the magnetic field. If the wire runs along the magnetic field, it will experience any force at all. As for angles Inbetween, it will feel some force.
The fourth acts in the same direction relative to the magnetic field on the direction of the current in the wire. So changing the direction of either the magnetic field or the current will change the direction of the force.
What is Fleming’s left-hand rule?
Flemings left-hand rule is used to find the direction of the force on the current carrying conductor
Using your left hand point your first finger in the direction of the magnetic field and your second finger in the direction of the current your thumb will then point in the direction of the force
What happens when a current carrying conductor is placed near a magnet?
Experiences a force and that an equal and opposite force act on the magnet
What is the equation for a force on a conductor at a right angles to a magnetic field carrying a current?
force on a conductor at right angles to a magnetic field
carrying a current (newton, N) = magnetic flux density
(tesla, T or newton per ampere metre, N/A m) × current
(ampere, A) × length (metre, m)
F = B x I x L
What does a solenoid to in terms of individual coils?
The coils are together to form a very strong almost uniform field along the centre of the solenoid
And they cancelled to give a weaker outside of the solenoid
What are the factors that affect the size and direction of an induced potential difference?
Moving/rotating either a magnet in a coil or wire or a conductor in a magnetic field
if you move or rotate the magnet in the opposite direction, then the potential difference/current will be reversed
If you keep the magnet moving backwards and forwards, or keep it rotating in the same direction, you produce an alternating current
How does the magnetic field produce opposes the original change in electromagnetic induction
When the current is induced in a wire, that current produces its own magnetic field. The magnetic field created by an induced current always acts against the change that made it.. basically, it’s trying to return things to the way they were
What can a transformer do?
Change the size of an alternating voltage
How does an alternating current in one circuit can induce an current in another circuit in a transformer?
Transformers induction to change the size of the potential difference of an alternating current. They all have 2 coils of wire, the primary and secondary coils, joined with an iron core. With an alternating potential difference is applied across the primary coil, it produces an alternating magnetic field. The iron in the core is a magnetic material that is easily magnetised and demagnetised. Because the coil is producing an alternating magnetic field, the magnetisation in the coil also alternate. This change in magnetic field induce a potential difference in the secondary coil.
Why in the national grid is electrical energy transferred to high voltage is from power stations and then transfer that lower voltage is in each home
The national grid has to transfer loads of energy each second, which means it transmits electricity to high power to do this. You need either a high potential difference or a high current.
A high current makes why is heat up, so loads of energy is wasted to thermal stores. So to reduce these losses and make the National Grid more efficient, high voltage, lowresistance cables, and transformers are used.
Where is my step up and step down Transformers that are used in the transmission of electricity in the national grid
Step up Transformers at power stations boost the potential difference up really high about 400,000 V and keep the current relatively low
Step down Transformers then bring it back down to safe, usable levels at the consumers end
How to find power for Transformers with 100% efficiency
V(p) x I(p) = V(s) x I(s)
potential difference across primary coil (volt, V) × current in
primary coil (ampere, A) = potential difference across
secondary coil (volt, V) × current in secondary coil
(ampere, A)
