AQA GCSE PHYSICS · PAPER 1 · HIGHER TIER ONLY
Increasing the pressure of a gas
Particle model of matter · Lesson 6 of 6
Teacher copy - includes the notes for whoever is teaching from it.
Warm-up
Answer each one, then check.
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
Learning Objectives
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.
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.
A Bicycle Pump
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Work done becomes internal energy. |
A bicycle pump with the handle pushed in, doing work on the air and warming it.
Why the Gas Warms
A chain of ideas.
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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. |
Bicycle Pump
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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.
Exam Points
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.
Key Terms
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Work Energy transferred by a force. |
Internal energy Total kinetic and potential energy of particles. |
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Compression Squashing a gas into a smaller volume. |
Molecule A group of atoms bonded together. |
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Enclosed gas A gas trapped in a container. |
Temperature A measure of average kinetic energy. |
Your Task: Warm Pump
8 minutes
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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. |
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.
Note: Ask what would happen if the pump were used very slowly.
Can I...?
☐ 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.
Summary
✓ 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.
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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. |
Exam Practice: Increasing the pressure of a gas
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…
▸ 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.
Question 1 · 3 marks · Explain
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“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.
Question 1 · mark scheme
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
▸ Model answer. Work is done on the air by the force on the piston. This transfers energy to the air, so the internal energy of the air increases and the temperature rises, warming the pump.
Question 2 · 2 marks · State
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“What is meant by work done?” |
HOW TO ANSWER IT Command word: State. Worth 2 marks, so plan before writing.
Question 2 · mark scheme
2 marks available. Award a mark for each point made.
▸ Transfer of energy. 1 mark
▸ By a force. 1 mark
▸ Model answer. The transfer of energy by a force.
Question 3 · 4 marks · Explain
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“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.
Question 3 · mark scheme
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
▸ Model answer. The force on the plunger does work on the gas. Energy is transferred to the gas particles, so the average kinetic energy of the particles increases. The temperature of the gas depends on the average kinetic energy, so the temperature rises.
Question 4 · 2 marks · Explain
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“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.
Question 4 · mark scheme
2 marks available. Award a mark for each point made.
▸ Energy transferred to the surroundings. 1 mark
▸ Internal energy or temperature decreases. 1 mark
▸ Model answer. The energy is transferred by heating to the surroundings, so the internal energy and temperature of the gas decrease.
Question 5 · 3 marks · Describe
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“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.
Question 5 · mark scheme
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
▸ Model answer. When compressed, work is done on the gas so its internal energy increases. When it expands and does work on the piston, its internal energy decreases and it cools.