7.3 Magnetism and Electromagnetism (induced potential, transformers and the national grid)

Question 1

What happens when an electrical conductor moves relative to a magnetic field?

Answer 1

A potential difference is induced across the ends of the conductor

Question 2

What happens to an electrical conductor when there is a change to the magnetic field that it is placed in?

Answer 2

A potential difference is induced across the ends of the conductor

Question 3

What is the requirement for an induced potential difference to cause a current flow?

Answer 3

the conductor must form a closed loop or be part of a complete circuit

Question 4

What can be said about the direction of the magnetic field produced by an induced current?

Answer 4

• the direction of the field is such that it opposes the change that induced the current
• this change is either the movement of the conductor or a change to the field

Question 5

What are two ways that the generator effect is used to generate different types of current?

Answer 5

• in an alternator to produce alternating-current
• in a dynamo, to produce direct-current

Question 6

What electromagnetic effect does a microphone take advantage of and how?

Answer 6

• the generator effect
• it converts the pressure variations in sound waves into alternating current in a circuit

Question 7

Describe the makeup of a basic transformer?

Answer 7

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

Question 8

Why is iron used as the core for a transformer?

Answer 8

it is easily magnetised

Question 9

Explain how a transformer works.

Answer 9

• An alternating current flows through the primary coil
• this induces a changing magnetic field in the core
• this changing magnetic field induces a current to flow in the secondary coil

Question 10

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

Answer 10

• 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 11

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

Answer 11

the electrical power input is equal to the electrical power output