Thermal Properties of Matter – Complete Formula Sheet (JEE Main Only)
1. Temperature & Heat
- Temperature: Measure of degree of hotness
- Heat: Energy transferred due to temperature difference
- Heat always flows: Higher T → Lower T
SI unit of heat: Joule (J)
2. Temperature Scales
K = °C + 273
°C = (5/9)(°F − 32)
Zero points:
- 0 K → Absolute zero
- Triple point of water = 273.16 K
3. Thermal Expansion
(a) Linear Expansion
ΔL = α L ΔT
(b) Areal Expansion
ΔA = β A ΔT (β = 2α)
(c) Volume Expansion
ΔV = γ V ΔT (γ = 3α)
4. Expansion of Solids – PYQ Traps
- Hole expands as if material absent
- α is same in all directions (isotropic solid)
- If expansion prevented → thermal stress develops
Thermal stress: σ = Y α ΔT
5. Calorimetry
Heat absorbed/released:
Q = m c ΔT
- c → specific heat capacity
- Water has maximum specific heat
Principle: Heat lost = Heat gained
6. Latent Heat
Q = m L
- L → latent heat
- Temperature remains constant during phase change
Lfusion < Lvaporisation
7. Heat Transfer – Conduction
Q / t = k A (T₁ − T₂) / L
- k → thermal conductivity
- Metals → high k
- Wood, glass → low k
8. Heat Transfer – Convection
- Occurs in fluids only
- Due to density difference
- Land breeze & sea breeze based on convection
9. Heat Transfer – Radiation
Stefan–Boltzmann Law:
P = σ A T⁴
Wien’s Displacement Law:
λmax T = constant
- Perfect black body → maximum absorption
- Radiation does not require medium
10. Newton’s Law of Cooling
dT/dt ∝ (T − Tsurrounding)
Valid for small temperature differences
11. JEE Main Question Profiling
| Question Type | JEE Tests | Common Trap |
|---|---|---|
| Thermal expansion | α, β, γ relation | Forgetting β = 2α, γ = 3α |
| Calorimetry | Energy balance | Sign convention mistake |
| Latent heat | Phase change logic | Changing temperature incorrectly |
| Conduction numericals | Formula substitution | Wrong area or length usage |
| Radiation | T⁴ dependence | Using °C instead of K |
| Newton cooling | Conceptual MCQ | Applying for large ΔT |
12. JEE Main Weightage Insight
- 1–2 direct MCQs almost every year
- Mostly formula + concept blend
- Very high scoring chapter
StudyBeacon • JEE Main Physics • Exam-Profiled Thermal Notes
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