Temperature

• Temperature is related to the average kinetic energy of atoms and molecules in a system
• Thermal energy - energy possessed by an object due to its temperature
• Thermal energy is transferred from a region of higher temperature to a region of lower temperature.
• Thermal equilibrium - a stable state in which there is no thermal energy transfer between two regions
• Zeroth Law of thermodynamics - if two thermodynamic systems are both in thermal equilibrium with a third system, then the two systems are in thermal equilibrium
• A physical property that varies with the temperature may be used for the measurement of the temperature

  • change in volume
  • change in pressure of a gas
  • change in electrical resistance
  • change in emf of a thermocouple
• Thermodynamic (Kelvin) scale - theoretical scale that is independent of properties of any particular substance
• Absolute zero - temperature at which a system has minimum internal energy ( not zero) at 0K, impossible to remove any more energy from the system
• Triple point of pure water - temperature at which water exists as vapour, liquid and solid at 273.16 K (0.01c)
• Thermocouple advantages

  • readings can be taken remotely
  • faster response
  • wider range
  • small thermal capacity
  • physically small- so quicker acting and readings taken at a point
  • power supply not needed
• Thermocouple disadvantages

  • non-linear variation with the temperature
  • for accurate reading a higher resistance voltmeter required
• Thermistor advantages

  • readings can be taken remotely
  • very robust
  • fast response
  • accurate
  • sensitive at low temperatures
• Thermistor disadvantages

  • non-linear variation with temperature
  • narrower range
  • slower response time than thermocouple
  • larger thermal capacity
  • not suitable to measure varying temperatures