Temperature (Copy)

A2 Level Physics – Section 14: Thermal Physics (Detailed Notes)

14.1 Thermal Equilibrium

1. Energy Transfer Due to Temperature Difference

• Thermal energy always flows from a region of higher temperature to a region of lower temperature.
• Transfer continues until both objects reach the same temperature.

2. Thermal Equilibrium

• Thermal equilibrium occurs when no net transfer of thermal energy occurs between objects in contact.
• This happens when all regions are at the same temperature.
• Important principle in thermodynamics and thermometer calibration.

14.2 Temperature Scales

1. Temperature Measurement Using Physical Properties

• A thermometric property is a measurable physical quantity that changes with temperature.
• Examples:
  • Density of a liquid (e.g. mercury)
  • Volume of a gas at constant pressure
  • Electrical resistance of a metal wire (e.g. platinum resistance thermometer)
  • e.m.f. of a thermocouple (voltage generated between two metals)
• These properties are used to construct empirical temperature scales (e.g. Celsius).

2. Thermodynamic Temperature Scale

• Based on laws of thermodynamics, independent of any material.
• Defined using absolute zero and the triple point of water (273.16 K).
• Used in scientific equations (e.g. ideal gas law).

3. Conversion Between Celsius and Kelvin

• Relationship:
  T (K) = θ (°C) + 273.15
  • e.g. 0 °C = 273.15 K
  • e.g. 100 °C = 373.15 K

4. Absolute Zero

• Absolute zero (0 K): lowest possible temperature
• At this point:
  • Particles have minimum possible internal energy
  • Gas pressure and volume theoretically reach zero
• No energy can be removed from a system at 0 K

14.3 Specific Heat Capacity and Specific Latent Heat

1. Specific Heat Capacity (c)

• Definition: The amount of energy required to raise the temperature of 1 kg of a substance by 1 K.
• Equation:
  Q = mcΔT
  • Q = heat energy (J)
  • m = mass (kg)
  • c = specific heat capacity (J/kg·K)
  • ΔT = change in temperature (K or °C)

Key Notes:

• Large c → heats slowly, stores more energy (e.g. water)
• Small c → heats quickly, stores less energy (e.g. metals)

2. Specific Latent Heat (L)

• Definition: Energy required to change the state of 1 kg of a substance without changing its temperature.

Equation:
Q = mL

• Q = energy (J)
• m = mass (kg)
• L = specific latent heat (J/kg)

3. Types of Specific Latent Heat

• During phase changes, temperature remains constant even as energy is added or removed.

Example:
Boiling water at 100 °C → temperature stays constant until all water becomes steam.