Physics · Simulation and virtual lab Free
Gas laws: Boyle’s law, Charles’s law and the pressure law
Squeeze, heat and cool trapped air, read the gauge and the ruler, and discover the three gas laws and absolute zero.
- You will learn to
- Verify Boyle’s law: pV is constant at constant temperature.
- Verify Charles’s law and the pressure law using kelvin temperatures.
- Estimate absolute zero from a graph.
- You will measure
- Pressure (kPa), volume (cm³) and temperature (°C and K).
- Time needed
- About 35–45 min
- Equipment
- Nothing extra. Real version: syringe and Bourdon gauge, capillary tube with acid index, ruler, flask, water bath, thermometer.
- Price
- Free: no payment, no account.
Virtual lab
Follow the steps with the simulation above (go back to the simulation ↑). Each time you tap Record, a row is added to the table and a point to the graph.
Aim
To investigate how the pressure, volume and temperature of a fixed mass of gas are related, to verify Boyle’s law, Charles’s law and the pressure law, and to estimate absolute zero.
What to do
- Choose Boyle’s law. Set the volume to 50 cm³, wait for the gauge to settle and tap Record.
- Push the plunger (or use the slider) to 40, 30, 25, 20 and 15 cm³. Record each time. Look at the graph of p against 1/V.
- Choose Charles’s law. Tap Fill the bath with ice water, wait until the length of the air column stops changing, and record.
- Heat the bath to 20, 40, 60, 80 and 100 °C. Stir and wait each time before you record. Extend the graph line to find absolute zero.
- Choose the pressure law and repeat from 0 °C to 100 °C. Compare the temperature where the line meets zero pressure.
- Convert each temperature to kelvin (T = θ + 273) and check that pV, V ÷ T and p ÷ T are constant.
Results
📏 Read the instruments carefully
| Instrument | Smallest reading | Uncertainty |
|---|
| Bourdon pressure gauge (0–500 kPa) | 10 kPa | ± 5 kPa |
| Bourdon pressure gauge (0–200 kPa) | 5 kPa | ± 2.5 kPa |
| Syringe scale | 1 cm³ | ± 0.5 cm³ |
| Ruler beside the capillary tube | 1 mm | ± 0.5 mm |
| Thermometer | 1 °C | ± 0.5 °C |
Write every reading with its unit, and with the same number of decimal places as the instrument. Use the 🔍 Magnifier on the picture to read small scales at eye level.
⚠️ Avoid these mistakes
- Reading the gauge or the ruler before the readings are steady: wait for the gas to reach the temperature of the water.
- Using °C instead of kelvin in pV ÷ T: always use T = θ + 273.
- Leaving part of the air column above the water: the whole gas must be at the bath temperature.
✍️ Conclusion
Write your own conclusion first: what do your results and graph show, and which law or principle do they support?
Check your conclusion
For a fixed mass of gas, pV is constant at constant temperature (Boyle’s law), V ÷ T is constant at constant pressure (Charles’s law) and p ÷ T is constant at constant volume (pressure law), where T is in kelvin. Extending the graphs to zero volume or pressure gives absolute zero, about −273 °C.
Questions
State Boyle’s law.
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume: pV = constant.
Why must you wait after pushing the plunger before reading the gauge?
Squeezing the gas quickly warms it a little; the reading is correct only when the gas is back at room temperature and the needle is steady.
State Charles’s law.
For a fixed mass of gas at constant pressure, the volume is directly proportional to the absolute (kelvin) temperature: V ÷ T = constant.
Convert 27 °C and −73 °C to kelvin.
27 + 273 = 300 K; −73 + 273 = 200 K.
What is absolute zero and how does the experiment estimate it?
Absolute zero (−273 °C, 0 K) is the lowest possible temperature. Extending the straight line of V (or p) against θ back to V = 0 (or p = 0) meets the temperature axis at about −273 °C.
Explain with particles why the pressure of a gas rises when it is heated at constant volume.
The particles move faster, so they hit the walls more often and with more force each time; the force per unit area (pressure) increases.
For teachers: expected results and how the model works
Boyle: pV = 4040 kPa·cm³ (101 kPa at 40 cm³, 20 °C), with small random reading errors. Charles: tube area 1.00 cm², V = 10.00 cm³ at 0 °C, so V = 13.66 cm³ at 100 °C; the gas takes a few seconds to reach the bath temperature, and Record is refused until readings are steady. Pressure law: 101 kPa at 20 °C, 250 cm³ flask. Both lines extrapolate to −273 °C.
Quick check 3 questions · scored
Choose one answer for each question. You see at once if it is right, why, and your score at the end.
1. A gas has p = 100 kPa and V = 60 cm³. At the same temperature V becomes 30 cm³. New pressure?
pV is constant: 100 × 60 = p × 30, so p = 200 kPa.
2. What is 50 °C in kelvin?
T = 50 + 273 = 323 K.
3. Where does the V against θ line meet V = 0?
Extrapolation gives absolute zero, about −273 °C (0 K).
Your score:
Exam practice Exam set
National-exam style questions on this simulation (20 marks). Try each one on paper first, then open the marking scheme.
A gas occupies 300 cm³ at a pressure of 100 kPa. Calculate its volume when the pressure becomes 150 kPa at the same temperature. (3 marks)
Marking scheme: p₁V₁ = p₂V₂ (1); 100 × 300 = 150 × V₂ (1); V₂ = 200 cm³ (1).
A balloon has a volume of 2.0 dm³ at 17 °C. Find its volume at 47 °C at the same pressure. (4 marks)
Marking scheme: T₁ = 290 K, T₂ = 320 K (1); V₁ ÷ T₁ = V₂ ÷ T₂ (1); V₂ = 2.0 × 320 ÷ 290 (1) = 2.2 dm³ (1).
A car tyre is at 200 kPa at 20 °C. After a long journey its temperature is 50 °C. Calculate the new pressure (volume constant) and give one safety reason for checking tyres when cold. (4 marks)
Marking scheme: p₂ = p₁ T₂ ÷ T₁ (1) = 200 × 323 ÷ 293 (1) = 220 kPa (1). Pressure measured hot is higher than the true cold value, so tyres could be wrongly under-inflated / over-pressure risk (1).
Using the equation pV ÷ T = constant, find the volume at 300 K and 100 kPa of a gas that occupies 50 cm³ at 400 K and 160 kPa. (4 marks)
Marking scheme: p₁V₁ ÷ T₁ = p₂V₂ ÷ T₂ (1); 160 × 50 ÷ 400 = 100 × V₂ ÷ 300 (1); 20 = V₂ ÷ 3 (1); V₂ = 60 cm³ (1).
Describe how you would verify Charles’s law in the laboratory, naming the apparatus and the precautions. (5 marks)
Marking scheme: Capillary tube with air trapped by a sulfuric acid index, fixed to a ruler (1), in a water bath with a thermometer and stirrer (1). Heat in steps; stir and wait for a steady length before reading (1). Plot length (volume) against temperature and extend to 0 (1). Precautions: read at eye level / keep the whole air column under water (1).
Donat Sciences and MathsPhysics · Virtual lab worksheet
School: ........................................ Name: ................................ Class: ........ Date: ............
Gas laws: Boyle’s law, Charles’s law and the pressure law
Aim: To investigate how the pressure, volume and temperature of a fixed mass of gas are related, to verify Boyle’s law, Charles’s law and the pressure law, and to estimate absolute zero.
Apparatus (real laboratory): syringe and Bourdon gauge, capillary tube with acid index, ruler, flask, water bath, thermometer.
What to do (with the simulation on www.donatstem.co.rw)
- Choose Boyle’s law. Set the volume to 50 cm³, wait for the gauge to settle and tap Record.
- Push the plunger (or use the slider) to 40, 30, 25, 20 and 15 cm³. Record each time. Look at the graph of p against 1/V.
- Choose Charles’s law. Tap Fill the bath with ice water, wait until the length of the air column stops changing, and record.
- Heat the bath to 20, 40, 60, 80 and 100 °C. Stir and wait each time before you record. Extend the graph line to find absolute zero.
- Choose the pressure law and repeat from 0 °C to 100 °C. Compare the temperature where the line meets zero pressure.
- Convert each temperature to kelvin (T = θ + 273) and check that pV, V ÷ T and p ÷ T are constant.
Results
| # | Experiment | θ (°C) | T (K) | V (cm³) | p (kPa) | pV or V/T or p/T |
|---|
| 1 | | | | | | |
| 2 | | | | | | |
| 3 | | | | | | |
| 4 | | | | | | |
| 5 | | | | | | |
| 6 | | | | | | |
| 7 | | | | | | |
| 8 | | | | | | |
| 9 | | | | | | |
| 10 | | | | | | |
| 11 | | | | | | |
| 12 | | | | | | |
Graph
Boyle: plot p against 1/V. Charles: plot V against θ (°C) from −300 °C to 100 °C. Pressure law: plot p against θ. Extend the straight lines.
Questions
- State Boyle’s law. [2]
- Why must you wait after pushing the plunger before reading the gauge? [2]
- State Charles’s law. [2]
- Convert 27 °C and −73 °C to kelvin. [2]
- What is absolute zero and how does the experiment estimate it? [2]
- Explain with particles why the pressure of a gas rises when it is heated at constant volume. [2]
- A gas occupies 300 cm³ at a pressure of 100 kPa. Calculate its volume when the pressure becomes 150 kPa at the same temperature. [3]
- A balloon has a volume of 2.0 dm³ at 17 °C. Find its volume at 47 °C at the same pressure. [4]
- A car tyre is at 200 kPa at 20 °C. After a long journey its temperature is 50 °C. Calculate the new pressure (volume constant) and give one safety reason for checking tyres when cold. [4]
- Using the equation pV ÷ T = constant, find the volume at 300 K and 100 kPa of a gas that occupies 50 cm³ at 400 K and 160 kPa. [4]
- Describe how you would verify Charles’s law in the laboratory, naming the apparatus and the precautions. [5]
Donat Sciences and MathsPhysics · Virtual lab worksheet
School: ........................................ Name: ................................ Class: ........ Date: ............
Marking scheme: Gas laws: Boyle’s law, Charles’s law and the pressure law
Expected results
Boyle: pV = 4040 kPa·cm³ (101 kPa at 40 cm³, 20 °C), with small random reading errors. Charles: tube area 1.00 cm², V = 10.00 cm³ at 0 °C, so V = 13.66 cm³ at 100 °C; the gas takes a few seconds to reach the bath temperature, and Record is refused until readings are steady. Pressure law: 101 kPa at 20 °C, 250 cm³ flask. Both lines extrapolate to −273 °C.
Answers
- State Boyle’s law. [2]
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume: pV = constant.
- Why must you wait after pushing the plunger before reading the gauge? [2]
Squeezing the gas quickly warms it a little; the reading is correct only when the gas is back at room temperature and the needle is steady.
- State Charles’s law. [2]
For a fixed mass of gas at constant pressure, the volume is directly proportional to the absolute (kelvin) temperature: V ÷ T = constant.
- Convert 27 °C and −73 °C to kelvin. [2]
27 + 273 = 300 K; −73 + 273 = 200 K.
- What is absolute zero and how does the experiment estimate it? [2]
Absolute zero (−273 °C, 0 K) is the lowest possible temperature. Extending the straight line of V (or p) against θ back to V = 0 (or p = 0) meets the temperature axis at about −273 °C.
- Explain with particles why the pressure of a gas rises when it is heated at constant volume. [2]
The particles move faster, so they hit the walls more often and with more force each time; the force per unit area (pressure) increases.
- A gas occupies 300 cm³ at a pressure of 100 kPa. Calculate its volume when the pressure becomes 150 kPa at the same temperature. [3]
p₁V₁ = p₂V₂ (1); 100 × 300 = 150 × V₂ (1); V₂ = 200 cm³ (1).
- A balloon has a volume of 2.0 dm³ at 17 °C. Find its volume at 47 °C at the same pressure. [4]
T₁ = 290 K, T₂ = 320 K (1); V₁ ÷ T₁ = V₂ ÷ T₂ (1); V₂ = 2.0 × 320 ÷ 290 (1) = 2.2 dm³ (1).
- A car tyre is at 200 kPa at 20 °C. After a long journey its temperature is 50 °C. Calculate the new pressure (volume constant) and give one safety reason for checking tyres when cold. [4]
p₂ = p₁ T₂ ÷ T₁ (1) = 200 × 323 ÷ 293 (1) = 220 kPa (1). Pressure measured hot is higher than the true cold value, so tyres could be wrongly under-inflated / over-pressure risk (1).
- Using the equation pV ÷ T = constant, find the volume at 300 K and 100 kPa of a gas that occupies 50 cm³ at 400 K and 160 kPa. [4]
p₁V₁ ÷ T₁ = p₂V₂ ÷ T₂ (1); 160 × 50 ÷ 400 = 100 × V₂ ÷ 300 (1); 20 = V₂ ÷ 3 (1); V₂ = 60 cm³ (1).
- Describe how you would verify Charles’s law in the laboratory, naming the apparatus and the precautions. [5]
Capillary tube with air trapped by a sulfuric acid index, fixed to a ruler (1), in a water bath with a thermometer and stirrer (1). Heat in steps; stir and wait for a steady length before reading (1). Plot length (volume) against temperature and extend to 0 (1). Precautions: read at eye level / keep the whole air column under water (1).