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Physics · 5. Thermal physics and gases

Particles, temperature, heat transfer and gases

Explain thermal phenomena with particles and investigate pressure–volume behaviour.

40 minutesContent version: 2.1
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Driving question

How does the particle model explain temperature, pressure and heat transfer?

Curriculum coverage

Vietnam 2018 thermal physics; IGCSE thermal physics.

Model scope and limitations

Boyle’s law is an approximation for fixed gas at constant temperature away from condensation.

Learning objectives

  • Distinguish temperature, internal energy and energy transferred by heating.
  • Explain conduction, convection and radiation.
  • Use pV = constant for a fixed gas at constant temperature.

Prerequisite knowledge

  • Particle model and °C–K conversion.
  • Inverse proportion.

Core knowledge

Temperature

For an ideal gas, absolute temperature is proportional to mean translational kinetic energy; more generally, temperature is not total internal energy.

Gas pressure

Particle collisions with container walls create force per unit area.

Boyle’s law

Slow isothermal compression increases collision frequency per area: p ∝ 1/V.

Worked example

Gas at p₁ = 100 kPa and V₁ = 60 cm³ is compressed isothermally to 40 cm³. p₂ = p₁V₁/V₂ = 150 kPa.

Misconceptions to avoid

  • Heat is not a stored substance; it is energy transfer caused by a temperature difference.
  • pV is not constant when temperature or gas amount changes.

Virtual experiment procedure: Boyle’s law

  1. Keep temperature and gas amount fixed.
  2. Use five V values, allow equilibrium, then record p.
  3. Calculate pV and plot p against 1/V.

Safety and cautions

  • In a real lab, never pressurise a sealed vessel beyond its rating.

Evidence to collect

  • A table of V, p, 1/V and pV with units.
  • A judgement on whether pV is constant within data limits.
Open the virtual experiment

Diagnostic check

1. Which unit measures absolute temperature?

  1. K
  2. °C
  3. J
Show answer and explanation

Correct answer: K

Kelvin is the SI unit of thermodynamic temperature.

2. What is the microscopic origin of gas pressure?

  1. Particle collisions with walls
  2. Mass disappearing
  3. Heat appearing
Show answer and explanation

Correct answer: Particle collisions with walls

Collisions transfer momentum and exert force on walls.

3. Which variable must stay constant in a Boyle investigation?

  1. Temperature
  2. Volume
  3. Pressure
Show answer and explanation

Correct answer: Temperature

The p–V relation is isolated only at constant temperature.

Application practice

1. At constant temperature, halving V makes ideal p do what?

  1. Double
  2. Halve
  3. Stay constant
Show answer and explanation

Correct answer: Double

Since pV is constant, p is inversely proportional to V.

2. 20°C is approximately how many kelvin?

  1. 293 K
  2. 253 K
  3. 20 K
Show answer and explanation

Correct answer: 293 K

T(K) = t(°C) + 273.15 ≈ 293 K.

3. Which heat-transfer mechanism works through a vacuum?

  1. Radiation
  2. Convection
  3. Particle conduction
Show answer and explanation

Correct answer: Radiation

Electromagnetic radiation needs no material medium.

Academic references

  1. OpenStax Physics — peer-reviewed high-school physics
  2. BIPM — SI Brochure, 9th edition

This lesson is maintained against the cited sources below. Simulations are learning models and do not replace supervised physical-laboratory safety procedures.

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WebLab STEM
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Đức Tiến — Control & Automation Engineer