E.2 Thermal Energy & Heat Transfer
Exploring thermal equilibrium, specific heat capacity, and the three methods of heat transfer: conduction, convection, and radiation.
Questions to explore
- ? Why do some materials feel cold even when everything is at the same temperature?
- ? How does thermal energy travel through solids, liquids, gases — and empty space?
💡 Key ideas, explained simply
🌡️ Heat vs temperature
Temperature measures the *average* kinetic energy of particles (how hot something is), in °C or K.
Heat is the *total* thermal energy that flows from hot to cold. A bathtub of warm water holds far more heat than a boiling cup of tea, even though the tea is at a higher temperature.
🔥 Three ways heat travels
Conduction — through solids, as vibrating particles and free electrons pass energy along.
Convection — in fluids, as warm, less-dense fluid rises and cool fluid sinks, forming a current.
Radiation — as infrared waves that need no medium, which is how the Sun's heat crosses empty space.
Comparing heat transfer
| Method | Where | How it works | Needs a medium? |
|---|---|---|---|
| Conduction | Solids (esp. metals) | Particle vibrations & free electrons | Yes |
| Convection | Liquids & gases | Warm fluid rises, cool fluid sinks | Yes |
| Radiation | Any space, incl. vacuum | Infrared electromagnetic waves | No |
📖 Key terms
- Temperature
- Average kinetic energy of particles, in °C or kelvin (K).
- Heat (thermal energy)
- Total energy transferred from hot to cold.
- Specific heat capacity
- Energy to raise 1 kg by 1 °C, used in .
- Conduction
- Heat transfer through solids by particle collisions.
- Convection
- Heat transfer in fluids by bulk movement (density changes).
- Radiation
- Heat transfer by infrared waves; no medium needed.
1 Key Formulas
✏️ Worked example
Specific heat capacity
How much energy heats of water from to ? ()
- 1
Write the formula
- 2
Find the temperature change
- 3
Substitute
Q = 252 000 J (252 kJ). Water's high c is why it takes so long to boil.
Interactive Lab
Phase Change Lab
Heat a substance and watch particles gain energy, melt and boil at constant temperature.
🧥 Physics around you
A vacuum flask beats all three: the vacuum stops conduction and convection, silvered walls reflect radiation back, and the stopper blocks convection at the top. That is why your drink stays hot for hours.
🎯 Nail it in the exam
Specific Heat Capacity – Core Calculations
Specific heat capacity () is the energy needed to raise the temperature of 1 kg of a substance by 1 °C (or 1 K). The formula appears in nearly every thermal physics paper.
Typical exam question: “A 2 kg aluminium block is heated from 20 °C to 50 °C. If of aluminium is 900 J/(kg·°C), calculate the energy transferred.”
Steps: 1) Identify mass, , and temperature change. 2) Multiply: .
Key concept: Water has a high specific heat capacity, which is why it is used in cooling systems and why coastal climates are milder.
-
ΔT can be in °C or K because the size of one degree is the same.
-
Always include units for – J/(kg·°C).
-
If a question asks ‘Explain why …’, link the high/low specific heat capacity to the time taken to heat/cool.
Comparing Conduction, Convection, and Radiation
MYP frequently asks you to compare these three heat transfer methods (Criteria A: Knowing and understanding).
Conduction: transfer through solids (and to a small extent in fluids) by particle vibrations and free electrons. No overall movement of material.
Convection: transfer in fluids by bulk movement of the fluid itself (density changes).
Radiation: transfer by infrared electromagnetic waves; no medium needed.
Common application questions: vacuum flasks, solar water heaters, insulation in houses. For a vacuum flask, explain how each feature minimises heat transfer (silvered walls reduce radiation, vacuum stops conduction/convection, stopper reduces conduction/convection).
-
Never say heat ‘rises’ – it is the hot fluid that rises.
-
Dark, matt surfaces are good absorbers and emitters of radiation; shiny, light surfaces are poor absorbers and poor emitters (good reflectors).
-
Draw labelled diagrams when asked to explain a convection current – arrows must show the cycle of hot rising and cold sinking.
🧠 Check your understanding
Tap an answer to see if you're right — and why.
Q1. Through which process does heat travel from the Sun to the Earth?
Q2. Which material is generally the best thermal conductor?
📝 Exam-style questions
Try each one, then reveal the model answer.