ME6 - Electromagnetic induction

Question 1

What is electromagnetic induction?

Answer 1

The creation of a voltage in a wire which is experiencing a change in magnetic field

Question 2

What is the dynamo effect?

Answer 2

Transforming kinetic energy into electrical energy (in a power station this kinetic energy is provided by turbines)

Question 3

How can you get EM induction?

Answer 3

• When an electrical conductor moves through a magnetic field (cutting the magnetic field lines) causing the electrical conductor changes

Question 4

How can you test EM induction?

Answer 4

By connecting an ammeter to a conductor and moving the conductor through a magnetic field - it will show the magnitude and direction of the induced current

Question 5

What happens if the direction of movement is reversed?

Answer 5

The induced voltage/current will be reversed too

Question 6

What three things can you increase to get a bigger voltage?

Answer 6

• The strength of the magnet
• The number of turns on a coil
• The speed of the movement

Question 7

What is the difference between a simple electric motor and a generator?

Answer 7

Motor - you have a current in the wire and magnetic field which causes movement

Generator - You have a magnetic field and movement which induces a current

Question 8

What does AC generators do?

Answer 8

They rotate a coil in a magnetic field which produces a current

Question 9

What is there construction similar to?

Answer 9

A motor

Question 10

What happens as the coil spins?

Answer 10

A current is induced in the coil. The current changes direction every half turn

Question 11

What do generators have instead of a split-ring commutator?

Answer 11

Slip rings and brushes to the contact doesn’t swap every half turn

Question 12

What do CRO displays show?

Answer 12

An ac voltage - the faster the revolutions produce more peaks and higher overall voltage

Question 13

How do power stations use ac generators?

Answer 13

They produce electricity - they get the energy needed to turn the coils or magnetic field in different ways

Question 14

A magnet is held above a coil. The coil is connected to a voltmeter. The magnet is released and falls into the coil

Explain why the voltmeter records a reading

Answer 14

As the magnet falls through the coil, there is a changing magnetic field acting on the coil. This inducers a voltage across the coil and a current through it

Question 15

The magnet is released from a greater height. How does this affect the voltmeter. Explain your answer

Answer 15

The magnet will be moving faster so the induced voltage will be greater

Question 16

State how the voltmeter reading changes when the same magnet?

(i) moves more slowly into the coil
(ii) moves into a coil with more turns
(iii) is reversed so that the S pole enters the coil first

Answer 16

(i) Reading decreases - less voltage
(ii) Reading increases - more voltage
(iii) Reading will be negative

Question 17

A student investigates how to produce a voltage. He hangs a magnet from the spring, above a coil that is connected to a data logger. The student pulls the magnet through the coil then releases it

Explain why the data is varied?
How do you know it is an alternating current?

Answer 17

1) The magnetic field is being cut forcing the amplitude to decrease as the spring with the magnet attached, slows down gradually
2) It goes from positive to negative

Question 18

Why does the voltage change on a graph?

Answer 18

• Direction of magnet changes
• Amount of field lines cut changes
• Speed of magnet changes

(Any one of these answers)