13. Electromagnetic Induction

Question 1

What factors affect the size of an induced potential difference?

Answer 1

• The number of turns on the coil of wire.
• Magnetic field strength.
• The speed of the movement/rotation.

Question 2

What are the factors that affect the direction of an induced potential difference?

Answer 2

• Changing direction of magnetic field / magnet.
• Changing polarity of magnet.

Question 3

Describe the correlation between the original change and the magnetic field produced.

Answer 3

The magnetic field produced opposes the original change.

• When a current is induced in a wire, that current produces its own magnetic field.
• The magnetic field produced by an induced current always acts against the change that made it.

Question 4

What is electromagnetic induction also referred to as?

Answer 4

The generator effect.

Question 5

Describe the makeup of a basic transformer.

Answer 5

A primary coil and a secondary coil of wire wrapped around an iron core.

Question 6

Why is iron used as the core for a transformer?

Answer 6

It is easily magnetised.

Question 7

Explain how a transformer works.

Answer 7

• An alternating current flows through the primary coil.
• This induces a changing magnetic field in the core.
• This changing magnetic field induces a changing potential difference in the secondary coil.
• The induces potential difference produces an alternating current in the external circuit.

Question 8

Why must the current flowing through the primary coil of a transformer be alternating?

Answer 8

• For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing.
• For the magnetic field to be changing, the current in the primary coil must be alternating.

Question 9

What can be said about the electrical power input and output of a 100% efficient transformer?

Answer 9

The electrical power input is equal to the electrical power output.

Question 10

What is a benefit of a step down transformer in the national grid?

Answer 10

It means that the voltage can be reduced to a value which is safe enough to be used in houses.

Question 11

Why is it important to have step up transformers in the national grid?

Answer 11

It can increase efficiency.
- For the same power, a higher voltage will lead to a lower current (P=VxI).
- The lower the current, the less energy that is lost.
- Used for transmission across power lines.

Question 12

Do step-up transformers increase or decrease the voltage and current?

Answer 12

Increase the voltage, decrease the current

Question 13

Do step-down transformers increase or decrease the voltage and current?

Answer 13

Decrease the voltage, increase the current

Question 14

Where are step-up and step-down transformers used in the national grid?

Answer 14

Step-up transformers are used at power stations, whilst step-down transformers are used in local substations before sent to factories and homes, shops and offices domestically.