Increasing the pressure of a gas - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 1 · HIGHER TIER ONLY

Increasing the pressure of a gas

Particle model of matter

Lesson 6 of 6

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Warm-up

Particle model of matter

Lesson 6 of 6

Answer each one, then check.

1

What is work done?

2

What is internal energy?

3

What is the link between temperature and particle energy?

4

What happens to gas pressure when volume decreases?

5

What is a force?

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Warm-up - Answers

Particle model of matter

Lesson 6 of 6

1

What is work done?

Energy transferred by a force

2

What is internal energy?

Total kinetic and potential energy of the particles

3

What is the link between temperature and particle energy?

Higher temperature means more kinetic energy

4

What happens to gas pressure when volume decreases?

It increases

5

What is a force?

A push or a pull

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Learning Objectives

Particle model of matter

Lesson 6 of 6

1

Define work as the transfer of energy by a force.

2

Explain that doing work on a gas increases its internal energy.

3

Explain why the temperature of a gas rises when it is compressed, for example in a bicycle pump.

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Particle model of matter

Lesson 6 of 6

WORK ON A GAS (HIGHER TIER)

Work is the transfer of energy by a force. Doing work on a gas increases the internal energy of the gas and can cause its temperature to rise.

This is why a bicycle pump gets warm when used.

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A Bicycle Pump

Particle model of matter

Lesson 6 of 6

Work done becomes internal energy.

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Why the Gas Warms

Particle model of matter

Lesson 6 of 6

A chain of ideas.

1

Push the piston

You apply a force that moves the piston: work is done on the gas.

2

Energy transferred

The energy is transferred to the gas particles.

3

Kinetic energy increases

The particles move faster.

4

Temperature rises

The average kinetic energy of the gas increases.

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Bicycle Pump

Particle model of matter

Lesson 6 of 6

Explain why the barrel of a bicycle pump gets hot when the pump is used to inflate a tyre.

1

Work done

The force on the piston does work on the air inside

2

Internal energy

The internal energy of the air increases as the energy is transferred to its molecules

3

Temperature

The temperature of the air rises, and thermal energy is transferred to the barrel

ANSWER

Work is done on the air, increasing its internal energy and temperature, which warms the pump.

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Exam Points

Particle model of matter

Lesson 6 of 6

How to score the marks.

Say 'work is done'

Name the force and the energy transfer.

Link to internal energy

Increase in internal energy of the gas.

Link to temperature

Average kinetic energy of the molecules increases, so temperature rises.

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Key Terms

Particle model of matter

Lesson 6 of 6

Work

Energy transferred by a force.

Internal energy

Total kinetic and potential energy of particles.

Compression

Squashing a gas into a smaller volume.

Molecule

A group of atoms bonded together.

Enclosed gas

A gas trapped in a container.

Temperature

A measure of average kinetic energy.

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Particle model of matter

Lesson 6 of 6

YOUR TASK

Warm Pump

8 minutes

You pump up a tyre and the base of the pump gets warm. Explain why using the ideas of work and internal energy.

1

Say what is being done to the gas.

2

Link to temperature.

WHAT A GOOD ANSWER SHOWS

Work is done on the air by the force pushing the piston. This increases the internal energy of the air (kinetic energy of the molecules), so the temperature increases and the pump warms.

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Can I...?

Particle model of matter

Lesson 6 of 6

Define work.

Explain work on a gas.

Link work to internal energy.

Link internal energy to temperature.

Use the bicycle pump example.

Write a clear chain of reasoning.

Use the correct terms.

Explain warming.

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Summary & Exam Focus

Work is energy transferred by a force.

Work done on a gas increases its internal energy.

The temperature of the gas increases.

Example: a bicycle pump.

EXAM FOCUS

Explain why the air in a bicycle pump gets hotter when the pump is used. (3 marks)

Work is done; internal energy rises; temperature rises.

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Exam Practice: Increasing the pressure of a gas

Particle model of matter

Lesson 6 of 6

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

Question 1 · 3 marks · Explain

A student uses a bicycle pump to inflate a tyre and notices that the pump becomes warm. Explain why.

Question 2 · 2 marks · State

What is meant by work done?

Question 3 · 4 marks · Explain

A gas in a sealed syringe is compressed quickly by pushing in the plunger. Explain, using the particle model, why the temperature of the…

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Exam Practice: Increasing the pressure of a gas (cont.)

Particle model of matter

Lesson 6 of 6

Question 4 · 2 marks · Explain

Explain why a gas compressed slowly and allowed to cool would not stay hot.

Question 5 · 3 marks · Describe

Describe the energy changes when a gas is compressed by a piston and then allowed to expand pushing the piston out.

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Question 1 · 3 marks · Explain

Particle model of matter

Lesson 6 of 6

“

A student uses a bicycle pump to inflate a tyre and notices that the pump becomes warm. Explain why.

HOW TO ANSWER IT

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

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Question 1 · mark scheme

Particle model of matter

Lesson 6 of 6

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

Work is done on the gas

1 mark

Internal energy of the gas increases

1 mark

Temperature rises

1 mark

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Question 2 · 2 marks · State

Particle model of matter

Lesson 6 of 6

“

What is meant by work done?

HOW TO ANSWER IT

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

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Question 2 · mark scheme

Particle model of matter

Lesson 6 of 6

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

Transfer of energy

1 mark

By a force

1 mark

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Question 3 · 4 marks · Explain

Particle model of matter

Lesson 6 of 6

“

A gas in a sealed syringe is compressed quickly by pushing in the plunger. Explain, using the particle model, why the temperature of the gas rises.

HOW TO ANSWER IT

Command word: Explain. Worth 4 marks, so plan before writing.

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Question 3 · mark scheme

Particle model of matter

Lesson 6 of 6

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

Work is done on the gas

1 mark

Energy transferred to the particles

1 mark

Average kinetic energy increases

1 mark

So the temperature rises

1 mark

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Question 4 · 2 marks · Explain

Particle model of matter

Lesson 6 of 6

“

Explain why a gas compressed slowly and allowed to cool would not stay hot.

HOW TO ANSWER IT

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

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Question 4 · mark scheme

Particle model of matter

Lesson 6 of 6

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

Energy transferred to the surroundings

1 mark

Internal energy or temperature decreases

1 mark

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Question 5 · 3 marks · Describe

Particle model of matter

Lesson 6 of 6

“

Describe the energy changes when a gas is compressed by a piston and then allowed to expand pushing the piston out.

HOW TO ANSWER IT

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

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Question 5 · mark scheme

Particle model of matter

Lesson 6 of 6

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

Work done on the gas: internal energy increases

1 mark

Gas does work on the piston when expanding

1 mark

Internal energy decreases

1 mark

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