Thermal Properties of Matter
Build a reliable understanding of temperature, heat, expansion, calorimetry, change of state and heat transfer for JEE Main Physics.
The central idea of this chapter
Heat is energy transferred due to a temperature difference. That heat can raise temperature, change state, or change dimensions. Keeping this chain clear makes most numerical questions easier.
What should you understand first?
Thermal Properties of Matter covers temperature and heat, thermal expansion, calorimetry, change of state and the three modes of heat transfer.
Core concepts
- Temperature and heat High
- Thermal expansion High
- Calorimetry High
- Change of state High
- Heat transfer Medium
Three transfer mechanisms
- Conduction kAΔT/L
- Convection Fluid motion
- Radiation εσAT⁴
- Newton's cooling dT/dt
- Thermal stress YαΔT
Thermal Properties of Matter formula sheet
Use kelvin or degree Celsius consistently for temperature differences. A temperature interval of 1 K equals an interval of 1°C.
| Topic | Formula / Relation | Meaning or use |
|---|---|---|
| Linear expansion | ΔL = αL₀ΔT | α is the coefficient of linear expansion |
| Area / volume expansion | ΔA = βA₀ΔT, ΔV = γV₀ΔT | For isotropic solids, β ≈ 2α and γ ≈ 3α |
| Heat capacity | Q = mcΔT | m is mass, c is specific heat capacity |
| Latent heat | Q = mL | Temperature stays constant during phase change |
| Calorimetry | Heat lost = Heat gained | Mixing and thermal equilibrium problems |
| Conduction | Q/t = kAΔT/L | Heat current through a slab or rod |
| Radiation | P = εσA(T⁴ − T₀⁴) | Net radiated power |
| Thermal stress | σ = YαΔT | Expansion prevented by a constraint |
Choosing the right relation
Most errors come from confusing heat with temperature, missing phase changes, or applying an expansion formula to the wrong dimension.
Key stages
- Sensible heating Q = mcΔT
- Latent heat plateau Constant T
- Steady conduction kAΔT/L
- Radiative loss εσAT⁴
- Thermal equilibrium No net flow
How to read a question
- Temperature changes? Use mcΔT
- Phase changes? Use mL
- Length/area/volume? α, β, γ
- Solid heat flow? Conduction
- No medium needed? Radiation
How to prepare this chapter
Revise temperature and expansion first, then move to calorimetry, change of state, and finally heat transfer.
What to do
- Start with temperature scales and thermal equilibrium
- Practise linear, area and volume expansion problems
- Master calorimetry and change-of-state numericals
- Compare conduction, convection and radiation
- Finish with chapter PYQs and a timed mock
Common mistakes
- Heat is not temperature; heat is transferred energy
- Latent heat has no ΔT during an ideal phase change
- Do not interchange α, β and γ across dimensions
- Use absolute temperature in radiation formulas
- Check which body loses and which body gains heat
Ready for thermal numericals?
Revise expansion, calorimetry and heat-transfer relations, then practise mixed JEE Main questions.
Thermal Properties of Matter FAQ
Short answers to common JEE Main preparation questions.
Thermal expansion is the change in dimensions of a body when its temperature changes. It may be linear, superficial or volumetric.
In an isolated system, heat lost by a hot body equals heat gained by a cold body until thermal equilibrium is reached.
The three modes are conduction, convection and radiation. Radiation can occur without a material medium.
Revise temperature and expansion first, practise calorimetry and change-of-state problems, then study heat transfer, Newton's law of cooling and radiation.