Keeping Things Moving Flashcards
With the motor effect, how can the size of the force on the wire be increased?
Increasing current
Increasing strength of magnets
In the motor effect, what causes movement?
Current
How does the motor effect work?
When a wire carrying an electric current is placed in a magnetic field, the magnetic field formed around the wire interacts with the magnet causing a force
With the motor effect, how can the direction of the wire be changed?
Reverse current
Reverse direction of magnetic field (swap magnets around)
In the motor effect, when will the wire not experience a force?
When it is parallel to the magnetic field
What is Fleming’s left hand rule used for?
To work out what direction the force induced will act
What is Fleming’s left hand rule?
Pointy finger is field (north to south)
Swearing finger is current
Thumb is the direction of the force
What do transformers need electromagnetic induction for?
To convert one voltage to another.
In electromagnetic induction, what does movement produce?
Current
If a wire or a coil of wire cuts through the lines of force of a magnetic field, or vice versa, what happens?
Potential difference is induced between the ends of the wire.
If the wire is part of a complete circuit, what will happen?
A current will be induced.
How is the current induced in one direction?
By moving the magnet into the coil
How is a current induced in the opposite direction?
By moving the magnet out of the coil.
By moving the other pole of the magnet into the coil.
How can the size of the induced potential difference be increased?
By increasing the speed of movement of the magnet or coil.
By increasing the strength of the magnetic field.
By increasing the number of turns on the coil.
What does a transformer do?
It changes electrical energy from one potential difference to another potential difference.
Why are transformers used in the National Grid?
To ensure efficient transmission of electricity.
What does a transformer consist of?
Two coils, called the primary and secondary coils, wrapped around a soft iron core.
What does the alternating potential difference across the primary coil cause?
An alternating current to flow.
What does the alternating current do?
It creates a continually changing magnetic field in the iron core.
What does the magnetic field in the iron core induce?
An alternating potential difference across the secondary coil.
What is the equation that shows how the size of the potential difference across the secondary coil depends on the relative number of turns on the primary and secondary coils?
Potential difference Number of turns on
across primary, Vp primary, Np
———————– = ————————
Potential difference Number of turns on
across secondary, Vs secondary, Ns
What is the difference between step-up and step-down transformers?
In a step-up transformer, there are more turns on the secondary coil than the primary coil, so the pd that leaves the secondary coil is greater than that of the primary coil.
In a step-down transformer, there are fewer turns on the secondary coil than the primary coil, so the pd leaving the secondary coil is lower than that of the primary coil.
If transformers are assumed to be 100% efficient at transferring energy, what equation shows that their power output would be equal?
Vp x Ip = Vs x Is
What are switch mode transformers?
Transformers that are lighter and smaller than traditional transformers.
They produce less heat and use very little power when no load is applied.
