Keeping Things Moving

Question 0

With the motor effect, how can the size of the force on the wire be increased?

Answer 0

Increasing current

Increasing strength of magnets

Question 1

In the motor effect, what causes movement?

Answer 1

Current

Question 2

How does the motor effect work?

Answer 2

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

Question 3

With the motor effect, how can the direction of the wire be changed?

Answer 3

Reverse current

Reverse direction of magnetic field (swap magnets around)

Question 4

In the motor effect, when will the wire not experience a force?

Answer 4

When it is parallel to the magnetic field

Question 5

What is Fleming’s left hand rule used for?

Answer 5

To work out what direction the force induced will act

Question 6

What is Fleming’s left hand rule?

Answer 6

Pointy finger is field (north to south)
Swearing finger is current
Thumb is the direction of the force

Question 7

What do transformers need electromagnetic induction for?

Answer 7

To convert one voltage to another.

Question 8

In electromagnetic induction, what does movement produce?

Answer 8

Current

Question 9

If a wire or a coil of wire cuts through the lines of force of a magnetic field, or vice versa, what happens?

Answer 9

Potential difference is induced between the ends of the wire.

Question 10

If the wire is part of a complete circuit, what will happen?

Answer 10

A current will be induced.

Question 11

How is the current induced in one direction?

Answer 11

By moving the magnet into the coil

Question 12

How is a current induced in the opposite direction?

Answer 12

By moving the magnet out of the coil.

By moving the other pole of the magnet into the coil.

Question 13

How can the size of the induced potential difference be increased?

Answer 13

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.

Question 14

What does a transformer do?

Answer 14

It changes electrical energy from one potential difference to another potential difference.

Question 15

Why are transformers used in the National Grid?

Answer 15

To ensure efficient transmission of electricity.

Question 16

What does a transformer consist of?

Answer 16

Two coils, called the primary and secondary coils, wrapped around a soft iron core.

Question 17

What does the alternating potential difference across the primary coil cause?

Answer 17

An alternating current to flow.

Question 18

What does the alternating current do?

Answer 18

It creates a continually changing magnetic field in the iron core.

Question 19

What does the magnetic field in the iron core induce?

Answer 19

An alternating potential difference across the secondary coil.

Question 20

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?

Answer 20

Potential difference Number of turns on
across primary, Vp primary, Np
———————– = ————————
Potential difference Number of turns on
across secondary, Vs secondary, Ns

Question 21

What is the difference between step-up and step-down transformers?

Answer 21

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.

Question 22

If transformers are assumed to be 100% efficient at transferring energy, what equation shows that their power output would be equal?

Answer 22

Vp x Ip = Vs x Is

Question 23

What are switch mode transformers?

Answer 23

Transformers that are lighter and smaller than traditional transformers.
They produce less heat and use very little power when no load is applied.

Question 24

How are switch mode transformers useful?

Answer 24

They are ideal for applications like mobile phone chargers due to their small size which makes them more portable and once the phone is fully charged the transformer acts as a switch and so does not waste energy.

Question 25

What frequency do normal transformers usually operate at?

Answer 25

50Hz

Question 26

What frequency do switch mode transformers operate at?

Answer 26

A higher frequency of between 50kHz and 200 kHz.