Electromagnetism - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Electromagnetism

Magnetism and electromagnetism

Lesson 2 of 8

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Warm-up

Magnetism and electromagnetism

Lesson 2 of 8

Answer each one, then check.

1

What is an electric current?

2

What is a circuit?

3

What is a coil of wire called?

4

Name a magnetic material.

5

What does a battery do?

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up - Answers

Magnetism and electromagnetism

Lesson 2 of 8

1

What is an electric current?

A flow of charge

2

What is a circuit?

A complete loop for current to flow round

3

What is a coil of wire called?

A solenoid

4

Name a magnetic material.

Iron

5

What does a battery do?

Provides a potential difference

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Learning Objectives

Magnetism and electromagnetism

Lesson 2 of 8

1

Describe the magnetic field around a straight wire carrying a current.

2

Explain how the field changes with current and distance.

3

Describe the field of a solenoid and compare it with a bar magnet.

4

Explain how to increase the strength of a solenoid's field and how an iron core affects it.

5

Describe an electromagnet.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Magnetism and electromagnetism

Lesson 2 of 8

CURRENT AND MAGNETISM

When a current flows in a wire it produces a magnetic field around the wire. The field is stronger with a bigger current and closer to the wire.

The field lines around a straight wire are concentric circles. Reversing the current reverses the direction of the field.

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Fields Around a Wire and a Solenoid

Magnetism and electromagnetism

Lesson 2 of 8

A solenoid's field looks like a bar magnet's field.

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Changing the Strength

Magnetism and electromagnetism

Lesson 2 of 8

Learn what makes a stronger field.

Change

Effect

Bigger current

Stronger field

More turns of wire in the coil

Stronger field

Iron core inside the solenoid

Much stronger field

Reverse the current

Field direction reverses

Move further from the wire

Weaker field

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Making an Electromagnet

Magnetism and electromagnetism

Lesson 2 of 8

Describe how to make a strong electromagnet.

1

Wind a coil

Many turns of insulated wire round an iron core (nail)

2

Connect to a cell

Current in the coil magnetises the core

3

Increase the strength

More turns, larger current, or an iron core

ANSWER

Coil with an iron core and a large current.

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Why Use an Electromagnet?

Magnetism and electromagnetism

Lesson 2 of 8

Give two advantages of an electromagnet over a permanent magnet.

1

Switch on and off

The field disappears when the current is turned off

2

Change the strength

Change the current to change the field

ANSWER

It can be switched off and its strength controlled.

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Uses

Magnetism and electromagnetism

Lesson 2 of 8

Where are electromagnets used?

Scrapyards

Lift and drop scrap iron.

Electric bells

Current magnetises an iron core that attracts a hammer.

Relays

A small current switches a large current.

Maglev trains

Strong electromagnets lift and move the train.

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Key Terms

Magnetism and electromagnetism

Lesson 2 of 8

Electromagnet

A solenoid with an iron core that is magnetic only when a current flows.

Solenoid

A coil of wire.

Magnetic field

The region around a magnet or current where a force acts on magnetic materials.

Current

The rate of flow of charge.

Core

A piece of iron inside a solenoid.

Turns

Loops of wire in a coil.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Magnetism and electromagnetism

Lesson 2 of 8

YOUR TASK

Build One

15 minutes

Wrap insulated wire round a nail and connect it to a cell. Count how many paper clips it picks up with 10, 20 and 30 turns.

1

Keep the current the same.

2

Do not leave it connected: the wire gets hot.

WHAT A GOOD ANSWER SHOWS

More turns pick up more paper clips. Stop current flowing and the clips drop.

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Can I...?

Magnetism and electromagnetism

Lesson 2 of 8

Describe the field round a wire.

State that the field circles the wire.

Say what a solenoid is.

Compare with a bar magnet.

List ways to strengthen the field.

Say what an iron core does.

Describe an electromagnet.

Give uses.

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Summary & Exam Focus

Current produces a magnetic field.

More turns, more current or an iron core gives a stronger field.

A solenoid field is like a bar magnet's field.

Reversing the current reverses the field.

EXAM FOCUS

State two ways to increase the strength of an electromagnet. (2 marks)

Number of turns, current, iron core.

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Exam Practice: Electromagnetism

Magnetism and electromagnetism

Lesson 2 of 8

Answer all questions. Use the mark allocation as a guide to how much to write. · 14 minutes

Question 1 · 2 marks · State

State two ways of increasing the strength of the magnetic field of a solenoid.

Question 2 · 2 marks · Describe

Describe the magnetic field around a straight wire carrying a current.

Question 3 · 3 marks · Explain

Explain why a solenoid with an iron core is used in a scrapyard to lift cars and then drop them.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Electromagnetism (cont.)

Magnetism and electromagnetism

Lesson 2 of 8

Question 4 · 3 marks · Describe

Describe the magnetic field of a solenoid and explain how it is similar to the field of a bar magnet.

Question 5 · 3 marks · Explain

A student increases the current in a solenoid. Explain what happens to the field and to the number of paper clips the solenoid can lift.

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Question 1 · 2 marks · State

Magnetism and electromagnetism

Lesson 2 of 8

“

State two ways of increasing the strength of the magnetic field of a solenoid.

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 2 of 8

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

One way

1 mark

A second way

1 mark

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Question 2 · 2 marks · Describe

Magnetism and electromagnetism

Lesson 2 of 8

“

Describe the magnetic field around a straight wire carrying a current.

HOW TO ANSWER IT

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

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Question 2 · mark scheme

Magnetism and electromagnetism

Lesson 2 of 8

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

Circles around the wire

1 mark

Weaker with distance

1 mark

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Question 3 · 3 marks · Explain

Magnetism and electromagnetism

Lesson 2 of 8

“

Explain why a solenoid with an iron core is used in a scrapyard to lift cars and then drop them.

HOW TO ANSWER IT

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

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Question 3 · mark scheme

Magnetism and electromagnetism

Lesson 2 of 8

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

Iron core strengthens the field

1 mark

Electromagnet only works when a current flows

1 mark

Switching off releases the car

1 mark

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Question 4 · 3 marks · Describe

Magnetism and electromagnetism

Lesson 2 of 8

“

Describe the magnetic field of a solenoid and explain how it is similar to the field of a bar magnet.

HOW TO ANSWER IT

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

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Question 4 · mark scheme

Magnetism and electromagnetism

Lesson 2 of 8

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

Lines pass through and loop round outside

1 mark

Same shape as a bar magnet with two poles

1 mark

Strong and uniform inside the coil

1 mark

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Question 5 · 3 marks · Explain

Magnetism and electromagnetism

Lesson 2 of 8

“

A student increases the current in a solenoid. Explain what happens to the field and to the number of paper clips the solenoid can lift.

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 2 of 8

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

Field is stronger

1 mark

Greater force on the paper clips

1 mark

More clips lifted

1 mark

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