3.16 Electromagnetic Induction

Question 1

What is electromagnetic induction?

Answer 1

The induction of a potential difference (and current if there’s a complete circuit) across a conductor which is experiencing a change in magnetic field.

Question 2

Electromagnetic Induction (2)

Answer 2

• Electromagnetic induction creates a potential difference (p.d.) across the ends of a conductor when there is a change in the magnetic field around the conductor. You can think of a p.d. being induced whenever a magnetic field is ‘cut’ or crossed by the conductor.
• If the coil is part of a complete circuit, it also induces a current.

Question 3

What are the two different situations where you get electromagnetic induction?

Answer 3

• The first is if the magnetic field through an electrical conductor changes (changes size or reverses). This is how transformers work.
• The second is if an electrical conductor (e.g. a coil of wire) and a magnetic field move relative to each other. You can do this by moving a magnet in a conductor or moving a conductor in a magnetic field.

Question 4

Describe how electromagnetic induction works when an electrical conductor and a magnetic field move relative to each other (3)

Answer 4

• If you move a magnet into a coil, it induces a potential difference across the ends of the coil.
• If you move the magnet (or coil) in the opposite direction, then the potential difference/current will be reversed. Likewise, if you flip the magnet so the other pole enters the coil, the potential difference/coil will be reversed too.
• If you keep the magnet (or coil) moving backwards and forwards, you produce a potential difference that keeps swapping directions.

Question 5

Describe how electromagnetic induction works by turning a magnet end to end in a coil (or turning a coil inside a field) (3)

Answer 5

• As you turn the magnet, the magnetic field through the coil changes. This change in the magnetic field induces a potential difference, which can make a current flow in the wire.
• When you’ve turned the magnet through half a turn, the direction of the magnetic field through the coil reverses. When this happens, the potential difference reverses, so the current flows in the opposite direction around the coil of wire.
• If you keep turning the magnet in the same direction - always clockwise, say - then the potential difference will keep on reversing every half turn and you’ll get an alternating current.

Question 6

What was discovered after electromagnetic induction was?

Answer 6

Power generators

Question 7

What is the consequence of using electromagnetic induction?

Answer 7

There is some debate over the use of pylons and overhead cables to transmit electricity across the country. The debate is whether living near to a pylon can lead to an increased risk of getting cancer

Question 8

How could we change the size of the induced potential difference? (3)

Answer 8

• Change the strength of the magnetic field: by using stronger magnets, that produce a stronger magnetic field, a larger potential difference would be induced.
• Move the wire, or magnets, more quickly: the faster they move, the faster the magnetic field will change and so the bigger the potential difference will be.
• Shape the wire into a coil: the more turns it has, the bigger the potential difference will be

Question 9

A potential difference is generated when a wire experiences a _______ in magnetic field.

Answer 9

change

Question 10

A wire moving up and down repeatedly perpendicular to a magnetic field will:

Answer 10

Generate an alternating potential difference

Question 11

A wire moving parallel to a magnetic field will:

Answer 11

Not generate a potential difference