Induced potential - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Induced potential

Magnetism and electromagnetism

Lesson 6 of 8

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up

Magnetism and electromagnetism

Lesson 6 of 8

Answer each one, then check.

1

What does a voltmeter measure?

2

What is a magnetic field?

3

What is a current?

4

What is a coil?

5

What is a conductor?

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up - Answers

Magnetism and electromagnetism

Lesson 6 of 8

1

What does a voltmeter measure?

Potential difference

2

What is a magnetic field?

Region where a force acts on a magnet

3

What is a current?

A flow of charge

4

What is a coil?

Loops of wire

5

What is a conductor?

Allows current to flow

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Learning Objectives

Magnetism and electromagnetism

Lesson 6 of 8

1

Describe the generator effect.

2

Describe how a potential difference is induced in a wire or coil by moving a magnet.

3

Explain the direction of the induced current and its effect (Higher).

4

Describe the factors that increase the size of the induced potential difference.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Magnetism and electromagnetism

Lesson 6 of 8

THE GENERATOR EFFECT

The generator effect is when a potential difference is induced across a conductor that moves relative to a magnetic field, or when the magnetic field through a conductor changes. If the conductor is part of a complete circuit, a current is induced.

Nothing is induced if there is no change: a stationary magnet in a stationary coil produces no potential difference.

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Inducing a Potential Difference

Magnetism and electromagnetism

Lesson 6 of 8

No change, no induced potential difference.

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What Changes the Induced p.d.

Magnetism and electromagnetism

Lesson 6 of 8

Learn the factors.

Change

Effect on the induced potential difference

Faster movement of the magnet

Larger

Stronger magnet

Larger

More turns on the coil

Larger

Reverse the movement

Direction of p.d. reverses

Reverse the magnet

Direction of p.d. reverses

Magnet stationary

No induced p.d.

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Why Does a Current Flow?

Magnetism and electromagnetism

Lesson 6 of 8

Explain why a current is produced when a magnet is moved into a coil connected in a circuit.

1

Magnetic field changes

As the magnet moves in, the field through the coil changes

2

p.d. induced

A potential difference is induced across the coil

3

Complete circuit

The induced p.d. makes a current flow

ANSWER

A changing field induces a p.d., and a current in a complete circuit.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Direction of the Induced Current

Magnetism and electromagnetism

Lesson 6 of 8

Higher tier.

Its own field

The induced current produces a magnetic field of its own.

Opposes the change

This field opposes the change that produced it.

Energy

You have to do work to push the magnet in.

Conservation

That work is what gets transferred to electrical energy.

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Key Terms

Magnetism and electromagnetism

Lesson 6 of 8

Generator effect

The induction of a potential difference across a conductor when the magnetic field changes or the conductor moves in a magnetic field.

Induced potential difference

A p.d. produced by the generator effect.

Induced current

A current produced in a complete circuit by an induced p.d.

Coil

Loops of wire.

Flux

The magnetic field passing through a coil.

Galvanometer

A sensitive meter that shows small currents.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Magnetism and electromagnetism

Lesson 6 of 8

YOUR TASK

Magnet in a Coil

12 minutes

Push a bar magnet into a coil connected to a galvanometer. Record the deflection: slowly, quickly, out, stationary. What do you notice?

1

Keep the coil the same.

WHAT A GOOD ANSWER SHOWS

Faster gives a bigger deflection; out reverses it; stationary gives zero.

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Can I...?

Magnetism and electromagnetism

Lesson 6 of 8

State the generator effect.

Say what induces a p.d.

Say when a current flows.

List ways to increase it.

Reverse the direction.

Explain no movement, no p.d.

Explain the opposing field.

Link to energy.

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Summary & Exam Focus

A changing magnetic field induces a potential difference.

Bigger with faster movement, stronger magnet, more turns.

No movement gives no p.d.

Reversing the movement reverses the p.d.

EXAM FOCUS

State two ways of increasing the potential difference induced in a coil. (2 marks)

Faster movement, stronger magnet, more turns.

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Exam Practice: Induced potential

Magnetism and electromagnetism

Lesson 6 of 8

Answer all questions. Use the mark allocation as a guide to how much to write. · 15 minutes

Question 1 · 2 marks · State

A magnet is pushed into a coil of wire connected to a voltmeter. State two ways of increasing the reading on the voltmeter.

Question 2 · 3 marks · Explain

A student holds a bar magnet still inside a coil of wire connected to a voltmeter. The voltmeter reads zero. Explain why and what they…

Question 3 · 3 marks · Describe

Describe what happens to the reading on the voltmeter when the magnet is pulled out of the coil at the same speed as it was pushed in.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Induced potential (cont.)

Magnetism and electromagnetism

Lesson 6 of 8

Question 4 · 3 marks · Explain

Explain why a current flows when a magnet is moved into a coil that is part of a complete circuit.

Question 5 · 3 marks · Explain

Explain why it is harder to push a magnet into a coil connected in a complete circuit than into a coil that is not connected.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · 2 marks · State

Magnetism and electromagnetism

Lesson 6 of 8

“

A magnet is pushed into a coil of wire connected to a voltmeter. State two ways of increasing the reading on the voltmeter.

HOW TO ANSWER IT

Command word: State. Worth 2 marks, so plan before writing.

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Question 1 · mark scheme

Magnetism and electromagnetism

Lesson 6 of 8

2 marks available. Award a mark for each point made.

One way

1 mark

Another way

1 mark

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Question 2 · 3 marks · Explain

Magnetism and electromagnetism

Lesson 6 of 8

“

A student holds a bar magnet still inside a coil of wire connected to a voltmeter. The voltmeter reads zero. Explain why and what they should do to get a reading.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 2 · mark scheme

Magnetism and electromagnetism

Lesson 6 of 8

3 marks available. Award a mark for each point made.

No change in field

1 mark

No p.d. induced

1 mark

Move the magnet

1 mark

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Question 3 · 3 marks · Describe

Magnetism and electromagnetism

Lesson 6 of 8

“

Describe what happens to the reading on the voltmeter when the magnet is pulled out of the coil at the same speed as it was pushed in.

HOW TO ANSWER IT

Command word: Describe. Worth 3 marks, so plan before writing.

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Question 3 · mark scheme

Magnetism and electromagnetism

Lesson 6 of 8

3 marks available. Award a mark for each point made.

A reading is shown

1 mark

Same size

1 mark

Opposite direction

1 mark

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Question 4 · 3 marks · Explain

Magnetism and electromagnetism

Lesson 6 of 8

“

Explain why a current flows when a magnet is moved into a coil that is part of a complete circuit.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 4 · mark scheme

Magnetism and electromagnetism

Lesson 6 of 8

3 marks available. Award a mark for each point made.

Changing field through the coil

1 mark

p.d. induced

1 mark

Complete circuit so current flows

1 mark

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Question 5 · 3 marks · Explain

Magnetism and electromagnetism

Lesson 6 of 8

“

Explain why it is harder to push a magnet into a coil connected in a complete circuit than into a coil that is not connected.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 5 · mark scheme

Magnetism and electromagnetism

Lesson 6 of 8

3 marks available. Award a mark for each point made.

Induced current produces its own field

1 mark

Opposes the motion

1 mark

Work done is transferred to electrical energy

1 mark

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