- 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
Based on expansion of liquid on heating
Its types are:
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
It is used in cold region and high mountain where it can measure -117C to 78C
- 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
- 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.
- 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
- 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