What is thermometry?
Thermometry
The branch of heat relating to the measurement of the temperature of a body is called thermometry. The thermometer is an instrument used to measure the temperature of a body.
The essential requisites of a thermometer are given as under:
1) Construction,
2) Calibration, and
3) Sensitiveness.
For the construction of a thermometer, the proper choice of a substance, whose physical property varies uniformly with rising in temperature, is essential.
1) Construction
The physical property of a substance plays an important role in the construction of a thermometer. In a mercury thermometer, the principle of expansion of mercury with rising temperature is used. The platinum resistance thermometer is based on the principle of the change in resistance with a change in temperature. The gas thermometer is based on the principle of change in volume or pressure with a change in temperature.
2) Calibration
When a thermometer is constructed, it should be properly calibrated. The standard fixed points are selected for calibrating a thermometer. The melting point of ice, boiling point of water, melting point of silver, and the melting point of gold are taken as fixed points. The scales are built by dividing the interval between the two fixed points into equal parts. Centigrade scale is built by dividing the interval between the melting point of ice and the boiling point of water (under normal pressure) into 100 equal parts and each part represents 1 degree celsius. Similarly, the Fahrenheit scale is built by dividing this interval into 180 equal parts.
3) Sensitiveness
The instrument, once constructed and calibrated, should also be sensitive. The thermometer will be sensitive if:
- it can detect even small changes in temperature
- it shows the temperature of a body in a short time and
- it does not take a large quantity of heat for its own heating from the body whose temperature is being measured.
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