IGCSE Physics Thermal Physics Notes
Thermal physics explains temperature and heat transfer using the particle model. Learn the states of matter, heat transfer methods and specific heat capacity.
Key concepts
- Particle model
- Solids have fixed close particles, liquids have close but mobile particles, gases have far-apart fast particles.
- Heat transfer
- Energy moves by conduction (solids), convection (fluids) and radiation (electromagnetic waves).
- Specific heat capacity
- The energy needed to raise the temperature of 1 kg of a substance by 1 °C.
- Temperature measures average particle kinetic energy; heat is energy transferred.
- Convection occurs because warm fluid is less dense and rises.
- Dark, matt surfaces are the best emitters and absorbers of radiation.
Key formulas
Thermal energy
Q = m × c × ΔT
mass × specific heat capacity × temperature change.
Required practicals
- Determine the specific heat capacity of a metal block using an immersion heater.
- Investigate which surfaces are the best emitters of infrared radiation (Leslie's cube).
Worked example
How much energy raises 2 kg of water (c = 4200 J/kg°C) by 10 °C?
- 1Write the equation: Q = m × c × ΔT.
- 2Substitute: Q = 2 × 4200 × 10.
- 3Multiply: Q = 84 000.
- 4State the unit: Q = 84 000 J (84 kJ).
Answer: Q = 84 000 J
Common mistakes
✗ Confusing heat and temperature.
✓ Temperature is average particle energy; heat is energy transferred between objects.
✗ Using temperature instead of temperature change (ΔT).
✓ Q = mcΔT uses the change in temperature, not the final value.
✗ Mixing up conduction and convection.
✓ Conduction is through solids; convection needs a moving fluid.
Quick check
Try these, then reveal the answers.
State the equation linking energy, mass and temperature change.Reveal answer
Q = m × c × ΔT.
Why does warm air rise?Reveal answer
It is less dense than the cooler air around it.
Which surface is the best emitter of radiation?Reveal answer
A dark, matt surface.
Exam tips
- Use the temperature change, not the absolute temperature, in Q = mcΔT.
- Name the correct transfer method for the material involved.
- Explain density changes when describing convection currents.
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Frequently asked questions
What is specific heat capacity?+
The energy needed to raise the temperature of 1 kg of a substance by 1 °C.
How does convection work?+
Heated fluid expands, becomes less dense and rises, while cooler fluid sinks, setting up a convection current.
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