Thermal equilibrium
Thermal Physics - OCR A-Level Physics
Key Definition
Thermal equilibrium
Two objects are in thermal equilibrium when there is no net transfer of thermal energy between them. They are at the same temperature.
Two objects are in thermal equilibrium when there is no net transfer of thermal energy between them. They are at the same temperature.
Key Definition
Absolute zero
The lowest possible temperature (0 K or -273.15 \degree C) at which molecules have minimum internal energy and zero random kinetic energy.
The lowest possible temperature (0 K or -273.15 \degree C) at which molecules have minimum internal energy and zero random kinetic energy.
- TemperatureA measure of the average kinetic energy of the particles in a substance. An SI base quantity measured in kelvin (K). is a measure of the average random kinetic energyThe capacity to do work. Measured in joules (J).The energyThe capacity to do work. Measured in joules (J). an object possesses due to its motion. of molecules in a substance.
- The Kelvin scaleThe absolute temperature scale starting at absolute zero (0 K = −273.15 °C). ΔT in K = ΔT in °C. is the thermodynamic temperature scale with absolute zeroThe lowest possible temperature (0 K = -273.15 °C), at which particles have minimum possible kinetic energyThe capacity to do work. Measured in joules (J).. as its zero point.
- To convert: $T(K) = T(\degree C) + 273.$
- At absolute zeroThe lowest possible temperature (0 K = -273.15 °C), at which particles have minimum possible kinetic energy., particles have zero kinetic energyThe energy an object possesses due to its motion. but may still have some residual zero-point energyThe minimum kinetic energy particles have at absolute zero (0 K); particles cannot be completely stationary. (quantum effect, not required for A-level).
- Two objects at different temperatures placed in contact will exchange thermal energy until they reach thermal equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹..The state in which two objects in thermal contact have no net heat transfer between them because they are at the same temperature..
Common Mistake
MEDIUM
Wrong: Writing temperatures in Kelvin with a degree symbol (e.g. 300 \degree K).
Right: Kelvin has no degree symbol. Write 300 K, not 300 \degree K. Only Celsius uses the degree symbol.
Right: Kelvin has no degree symbol. Write 300 K, not 300 \degree K. Only Celsius uses the degree symbol.
Examiner Tips and Tricks
- Always convert temperatures to Kelvin before substituting into gas law or kinetic theory equations.
- This is the most common source of errors in thermal physics calculations.