Thermal Properties of Matter Revision Notes for NEET Physics PDF Download
🔥 THERMAL PROPERTIES OF MATTER · TPM
Temperature scales • Thermal expansion • Calorimetry • Heat transfer • Newton's law • NEET problems
🌡️ TEMPERATURE SCALES
Celsius (°C), Fahrenheit (°F), Kelvin (K) – absolute scale.
Relation: (C/100) = (F–32)/180 = (K–273)/100
K = C + 273.15, C = (5/9)(F–32)
📏 THERMAL EXPANSION
Linear expansion: ΔL = α L₀ ΔT (α = coefficient of linear expansion)
Area expansion: ΔA = β A₀ ΔT (β ≈ 2α)
Volume expansion: ΔV = γ V₀ ΔT (γ ≈ 3α)
Anomalous expansion of water: Water has maximum density at 4°C. Between 0–4°C, it expands on cooling (contracts on heating).
📈 Linear expansion of a rod
⚖️ CALORIMETRY & HEAT CAPACITY
Heat capacity: C = Q/ΔT (J/K)
Specific heat capacity (c): Q = m c ΔT (J/kg·K)
Water equivalent: W = mcal ccal (mass of water having same heat capacity).
Principle of calorimetry: Heat lost = Heat gained (in a closed system).
💧 LATENT HEAT (L)
Heat required to change phase without temperature change.
Latent heat of fusion (Lf): solid → liquid. For ice: 3.36 × 10⁵ J/kg (80 cal/g).
Latent heat of vaporization (Lv): liquid → gas. For water: 22.6 × 10⁵ J/kg (540 cal/g).
🔥 HEAT TRANSFER MECHANISMS
Conduction
Q = (k A ΔT t)/L (Fourier's law)
k = thermal conductivity (W/m·K)
Thermal resistance: Rth = L/(kA)
Convection
Heat transfer by bulk motion of fluid. Natural & forced.
Newton's law of cooling: dQ/dt = h A (T–T₀)
Radiation
Stefan‑Boltzmann law: P = σ A e T⁴
σ = 5.67×10⁻⁸ W/m²K⁴, e = emissivity.
Wien's displacement: λmax T = b (2.9×10⁻³ m·K).
🖍️ Conduction through a composite slab
📉 NEWTON'S LAW OF COOLING
Rate of cooling ∝ temperature difference: dθ/dt = –k (θ – θ₀)
For small differences, cooling curve is exponential.
📉 Cooling curve (temperature vs time)
💡 NEET TIPS & SHORTCUTS
- In calorimetry, always convert temperatures to Kelvin or Celsius consistently.
- For expansion, γ for liquids is given directly (not 3α).
- Radiation: power emitted ∝ T⁴, so even small temperature rise increases radiation significantly.
- In steady state conduction through composite slab, heat current (dQ/dt) is same through each layer.
⚠️ COMMON MISTAKES
- Using linear expansion formula for volume changes without multiplying by 3.
- Forgetting to include latent heat in calorimetry problems.
- Assuming Newton's law of cooling holds for large temperature differences.
- Confusing thermal conductivity with thermal resistance.
📌 QUICK REVISION CARD
Linear expansion: ΔL = α L₀ ΔT
Area expansion: ΔA = β A₀ ΔT, β = 2α
Volume expansion: ΔV = γ V₀ ΔT, γ = 3α
Heat capacity: Q = mcΔT (no phase change)
Latent heat: Q = mL (phase change)
Conduction rate: dQ/dt = kA (ΔT/L)
Stefan-Boltzmann: P = σ A e T⁴