P3.3 Keeping things moving Flashcards
What is a magnetic field?
A region where magnetic materials (like iron and steal) and also wires carrying currents experience a force acting on them
What way do the arrows on field diagrams always point?
From north to south
What is an electromagnet?
A magnet whose magnetic field can be turned on or off with an electric current
How can you increase the strength of the magnetic field around a coil of wire?
By adding magnetically soft iron core through the middle of the coil.
What happens when a current stops through an electromagnet?
it stops being magnetic
What are some uses of electromagnets?
-In some cranes- to attracts and pick up things made from magnetic materials.
What is the motor effect?
The force experienced by a current carrying wire in a magnetic field
How can you increase the force in the motor effect?
- Increase the current
- Increase the magnetic field
- Make sure the wire is at 90 degrees to the magnetic field
How do you experience the full force in the motor effect?
Make sure the wire is at 90 degrees to the magnetic field
What happens if the direction of the current or magnetic field in the motor effect is reversed?
The direction of the force is reversed too
What happens if the wire runs along parallel to the magnetic field in the motor effect?
There will be no force
What do each of the 3 fingers stand for in Fleming’s Left Hand Rule?
Thumb= motion
First Finger= field
Second finger= current
What do electric motors use to work?
the motor effect
What 2 factors speed up an electric motor?
- more current
- stronger magnetic field
What does the split-ring commutator do in an electric motor?
reverses the current after every half turn, which keeps the motor rotating in the same direction
What is electromagnetic induction?
The creation of a potential difference (voltage) across a conductor which is experiencing a change in magnetic field.
Describe how we can make electricity by electromagnetic induction
moving a magnet in coil of wire
OR
moving a coil of wire in a magnetic field
In electromagnetic induction, what happens if you move the magnet through a coil of wire in the opposite direction or reverse the polarity of the magnet?
The potential difference/current will be reversed too
In electromagnetic induction, what happens if you keep the magnet moving forwards and backwards?
You produce a potential difference that keeps swapping direction
-will produce an ALTERNATING CURRENT
How do generators in a power station produce electricity?
By electromagnetic induction.
Keep magnets moving backwards and forwards through a coil
What happens when a current flows through a wire?
A magnetic field is produced around the wire
Describe the basic structure of a transformer
A primary and secondary coil, joined with an iron core
Coils-copper, electric conductor and covered in plastic
The primary coil is connected to an alternating current
Describe how a transformer works?
An alternating current in the primary coil produces a changing magnetic field in the iron core and hence in the secondary coil.
This induces an alternating potential difference across the ends of the secondary coil
How can you tell if a transformer is a step up transformer?
They have more turns on the secondary coil than the primary coil
How can you tell if a transformer is a step down transformer?
They have more turns on the primary coil than the secondary coil.
Describe the potential difference in step up transformer
pd across the secondary coil is greater than the pd across he primary coil
Describe the potential difference in step down transformer
pd across the secondary coil is less than the pd across the primary coil
What are switch mode transformers?
A type of transformer that operate at higher frequencies than traditional transformers.
Between what frequencies do switch mode transformers operate at?
Between 50kHz and 200kHz
What are some benefits of switch mode transformers?
much lighter and smaller than traditional transformers working from a 50Hz mains supply.
Use little power when they are switched on but not connected to a charging device (when no load is applied)
Give an example of what a switch mode transformer is used for
mobile phone chargers
In the equation
Vp (divided by) Vs = np (divided by) ns
what does each letter stand for and what are the units?
Vp- potential difference across the primary coil (V)
Vs- potential difference across the secondary coil (V)
np- the number of turns on primary coil
ns- the number of turns on secondary coil
In the equation
Vp x Ip = Vs x Is
what does each letter stand for and what are the units?
Vp- potential difference in primary coil (V)
Ip- current in primary coil (A)
Vs- potential difference across secondary coil (V)
Is- current in secondary coil (A)
When is a magnetic field produced around a wire?
when a current flows through the wire
A conductor will not experience a force if it is …….. to the magnetic field
parallel
When is the direction of the force reversed?
if either the direction of the current or the direction of the magnetic field is reversed
Explain how the motor effect is used to make the drum in a washing machine spin
A motor spins round because it has a coil between magnets.
There is a force when a current flows in the circuit and this makes the coil spin faster due to the motor effect
