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Heat and Temperature


  • Heat is the form of energy which stimulates our sense organs so that we feel hot or cold.
  • Sum of kinetic energies present in each molecules of a body.
  • It flows from higher temperature to a body at lower temperature.
  • SI unit of Heat is Joule and measured by Calorimeter


  • Degree of hotness or coldness of a body.
  • Average kinetic energy present in each molecules.
  • It is the reason for transfer of heat.


  • The science of temperature and its measurement.
  • Instrument use in thermometry is Thermometer.
  • Different Thermometer use analysis of different properties of matter to analyze temperature.


  • Use to measure temperature.
  • Lower fixed point: Temperature at which pure ice melts at normal pressure
  • Upper fixed point: Temperature at which pure water boils at normal pressure

Types of thermometer

Liquid Thermometer:

Based on expansion of liquid on heating

Its types are:

Mercury Thermometer:

Mercury is used in thermometer due to

  • low specific heat capacity
  • high thermal conductivity
  • uniform expansion over wide range
  • can measure -39 C to 357C
  • does not stick on the wall of tube
  • shinning in nature

Alcohol Thermometer:

It is used in cold region and high mountain where it can measure -117C to 78C

Gas thermometer

  • based on change in pressure at constant volume which is directly proportional to change in temperature.
  • most sensitive thermometer
  • Can measure -268C to 1500C
  • 'He' gas is used
  • where = pressure at tC

Resistance thermometer

  • Based on variation of resistance of conductor with temperature by
  • Pure platinum is used due to it's high value of temperature coefficient
  • can measure 270 C to 700C.

Thermo-electric thermometer

  • based on the principle of thermo-electricity (i.e. production of thermo-emf in a thermocouple when the two junctions are at different temperature)
  • Temperature Range of -270C to 2300C

Radiation Thermometer

  • based on quantity of heat radiation emitted by a body
  • also called Pyrometer.
  • Measurement of high temperature

vapour pressure thermometer

  • Based on the principle of change of vapor pressure with change in temperature
  • Measure low temperature
  • eg. helium vapor pressure thermometer