Temperature

Temperature is a measure of hotness and can be related to the kinetic energy of molecules of a substance. A number of physical phenomena can be used for measuring the temperature of an object. An instrument used for measuring temperature is called a thermometer and is constructed by using one of the following principles:

the change of length, such as length of a mercury column,
the change of volume, such as volume of a fixed mass of gas at constant pressure,
the change of pressure, such as pressure of a fixed mass of gas at constant volume,
the change in electric resistance, as in a thermistor,
the flow of electricity due to Seebeck effect, as in a thermocouple,
the radiation, as in radiation pyrometers.
All thermometers require a scale. This scale should be defined by easily repeatable circumstances or fundamental properties. For instance the Centigrade scale has been defined from the melting (0 C) and boiling (100 C) points of pure water at atmospheric pressure. For temperature the following units can be used:

	C, K, F.

where symbol C is for Centigrade (or Celsius), K for kelvin and F for Fahrenheit. If the temperature is c on the Centigrade (or Celsius) scale, then the absolute temperature on the kelvin scale will be:

	c+273.15

the Fahrenheit scale will show:

	1.8 c+32

There is also another temperature scale, called Rankine (symbol R). If the temperature is f on the Fahrenheit scale, the Rankine scale will show:

	 f+459.69

Absolute temperature or thermodynamic temperature (degree kelvin, K) is a fundamental dimension. It can be related to the energy possessed by matter and is an SI base unit.