Temperature & Thermometers — A/L Physics

Temperature A measure of the average kinetic energy of the particles in a substance. It determines the direction of net thermal energy flow (from higher to lower temperature). Intuition: A hot cup of tea has a higher temperature than ice water because its molecules move faster on average.

Thermal Equilibrium The state where two or more bodies in thermal contact have no net heat flow between them, meaning they share the same temperature. This is the basis for all thermometry — a thermometer must reach thermal equilibrium with the object to read its temperature correctly.

Zeroth Law of Thermodynamics If body A is in thermal equilibrium with body B, and body B is in thermal equilibrium with body C, then A and C are also in thermal equilibrium. This law justifies the use of a single thermometer to measure the temperature of any object by comparing it to a standard.