Unit 12 & 13 - Magnetism And The Motor Effect/ Electromagnetic Induction Flashcards
What is a permanent magnet?
Something that is always magnetic
What materials do magnets attract?
Magnetic materials
Give 4 magnetic materials
Iron, steel, nickel and cobalt
What is a magnetic field?
The space around a magnet where it affects other magnetic objects
What are the full names for the ends of a magnet
North-seeking pole
South-seeking pole
What is an induced magnet
When a magnetic material is in a magnetic field and becomes a magnet itself, it is no longer a magnet when it leaves the magnetic field
Give 3 examples of how magnets are used
Electric motors, loudspeakers, knife holders
What is used to find the shape of a magnetic field
Plotting compasses
How do you use a plotting compass
Place near a magnet, mark the direction, use this point to line up next mark
What type of magnetic field do 2 magnets form
A uniform magnetic field
What is the earths magnetic field caused by
Electric currents in the molten outer core, nickel and iron
What depends on the magnetic effect of electrical currents?
Electric motors
What does the direction of the magnetic field depend on
Direction of current
What rule is used for direction of magnetic field
Right thumb rule
What does the strength of a magnetic field depend on
The size of the current
What is a solenoid
When a wire is made into a coil
What is the magnetic field shape of a solenoid
Uniform in the center and opposite directions outside
What is an electromagnet?
A could of wire with a current flowing though it
What cans strengthen the magnetic field of an electromagnet
Putting a piece of iron inside it
What is the motor effect
When a force is produced as a result of a current carrying wire being between 2 magnets
What happens in the motor effect
The current in the wire creates a magnetic field around the wire which interacts with the magnetic field between the magnets
When is the force from the motor effect the strongest?
When the wire is at right angles to the magnetic field
What rule shows the direction f the force from the motor effect
Fleming’s left hand rule
What does each finger represent in the left hand rule
F - force
B - magnetic field
I - current
What 3 factors does the size of the force from the motor effect depend on
Magnetic field strength
Current size
Length of the wire
What is the strength of the magnetic field measured in?
Newton’s per amp metre (N/A m)
Tesla (T)
What is the equation to calculate the force from the motor effect
F = B x I x L
What is the role of a split ring commutator on an electric motor
To switch the direction of the current (each half is connected to an end of the coiled wire, as it turns, it constantly brushed past the + and - end of the circuit)
How is a p.d induced on a wire
When a wire is moving into a magnetic field, however, if the wire stops moving (even in the magnetic field) there is no p.d
What is caused as a result of a p.d being induced
A current
Why are wires coiled in a magnetic field
So there is more current in the magnetic field so there is more current created
What 3 factors affect the amount of p.d induced?
The number of coils, strength of the magnetic field, how fast the magnetic field changes of moved past the coil
Besides a change in magnetic field, what can also induce a p.d
Is a wire is moved into a magnetic field
How does reversing the direction of the movement of the magnetic field affect the direction of the p.d
It reverses the direction also
What direction does a current flow
Out negative, in positive
What direction does a magnetic field travel in
Out N in S
What happens when a magnet is moving in and out of a coil of wire
A current is induced on the wire which creates it own magnetic field
On a coil of wire that has a current induced, what makes one end of the wire N
If the N end of a magnet is moving into the coil
What is the generator effect
When a conducting wire is moved into a magnetic field, a p.d is induced, if the wire is complete, a current is also created
How does the generator effect produce an alternating current?
Since the edges of the coil are continuously switching direction, up the down, the direction of p.d is also switching. The p.d is 0 every time the coil is parallel to the magnetic field
Why in an alternator are the ends of the wire connected to 2 different slip rings
To allow the current to pass out of the coil and change direction
What are generators used in
Power stations
What is a dynamo
A generator with a commutator
How does a commutator work in a generator
The ends of the coil are connected to each half so when it spins, the direction of the current changes, causing it to always stay positive
What do microphones do
They convert the pressure variations in sound waves into variations in current in electrical circuits
How do microphones work
Sound waves cause variations in pressure, this makes a diaphragm vibrate, the diaphragm moves a coil of wire backwards and forwards which has a magnet inside it (a current is induced as a magnet moves in a wire)
What is the national grid
A system of wires an cables that sends electricity to homes and schools from power stations
Along the national grid, when is there the most energy wasted
Along the transmission lines
What happens if the p.d is increased along the national grid
The current decreases
Why are transformers used?
To change the p.d and current so less energy is wasted by heating
What is a step-up transformer
A transformer that increases the voltage and decreases the current
What is a transformer made of
2 coils of insulated wire wound into an iron core, no electrical connection between the coils
What type of a current do transformers use
Alternating current
How does a transformer work
Since there is a current supplied to the primary coil, a magnetic field is produced. The current alternates in direction so the magnetic field does also. The magnetic field is transmitted along the iron core and to the secondary coil. Since the mf is changing, a p.d is induced, causing a current to flow out the other end
How does a step-up transformer work
There are more coils in the secondary coil than the first so when the p.d is induced, it is greater at the secondary coil, causing the current to decrease
Why do transformers only work with ac
The current must change direction in order for a p.d to be induced
What is the equation to work out the p.d in a transformer
PC p.d/ SC p.d = PC number of turns/ SC number of turns
What is charge measured in
Coulombs
What are the 3 equations for power
P = I x V P = E/ t P = I^2 x R
