🌡️ Thermal Properties of Matter

1. Temperature and Heat

Heat is the form of energy transferred between systems due to a temperature difference. Temperature is the degree of hotness or coldness. Scales: Celsius, Fahrenheit, Kelvin. Relation: (C/5) = (F-32)/9 = (K-273.15)/5.

2. Thermal Expansion

Most substances expand on heating.

• Linear Expansion: ΔL = α L ΔT
• Area Expansion: ΔA = β A ΔT
• Volume Expansion: ΔV = γ V ΔT

Relation for isotropic solids: γ = 3α and β = 2α. (Note: Water shows anomalous expansion between 0°C and 4°C, where its volume decreases).

3. Specific Heat Capacity and Calorimetry

Principle of Calorimetry: Heat Lost by hot body = Heat Gained by cold body (assuming no heat loss to surroundings).

Latent Heat (L): Heat required to change the state without changing temperature. Q = mL.

4. Heat Transfer

• Conduction: Transfer through physical contact. Fourier's Law: Heat current H = -KA(ΔT/Δx).
• Convection: Transfer by actual movement of fluid matter.
• Radiation: Transfer via electromagnetic waves (no medium required).

The total energy radiated per second by a black body is proportional to the fourth power of its absolute temperature.

Newton's Law of Cooling: Rate of cooling is directly proportional to the temperature difference between the body and surroundings.