# Thermometers in Physics | Definition, Types – Thermometry and Calorimetry

Thermometers in Physics:
The thermometers work on the thermometric property, i.e., the property which changes with temperature like any physical quantity such as length, volume, pressure and resistance, etc., which varies linearly with a certain range of temperature.

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## Thermometers in Physics | Definition, Types – Thermometry and Calorimetry

Different Types of Thermometers:
Some different types of thermometers are given below

• Mercury thermometer
• Constant volume gas thermometer
• Platinum resistance thermometer
• Pyrometer thermometer

(i) Mercury thermometer:
In this thermometer, the length of a mercury column from some fixed point is taken as thermometric property.

If length of mercury column at 0° and 100° are l0 and l100 respectively and at t° the length of mercury is lt. Then

t = $$\left(\frac{l_{t}-l_{0}}{l_{100}-l_{0}}\right)$$ x 100°C

(ii) Constant volume gas thermometer:
Constant volume gas thermometer works on the principle of change in pressure with temperature when the volume is kept constant. If p0, P100 and pt are the pressures of gas at temperatures 0° C, 100°C, and unknown temperature (t°C) respectively keeping the volume constant, then

t = $$\left(\frac{p_{t}-p_{0}}{p_{100}-p_{0}} \times 100\right)$$°C

Note:
For constant pressure gas thermometers, t = $$\frac{V_{t}-V_{0}}{V_{100}-V_{0}}$$ x 100°C

(iii) Platinum resistance thermometer:
It works on the principle of variation of resistance of metals with temperature.

If R0, R100 and Rt are the resistances of a platinum wire at temperature 0°C, 100°C and unknown temperature (t°C) respectively.
Then,

t = $$\left(\frac{R_{t}-R_{0}}{R_{100}-R_{0}} \times 100\right)$$°C = $$\left(\frac{R_{t}}{R_{t r}} \times 273.16\right)$$K

Here, temperature coefficient of resistance (α) is given by

α = $$\frac{R_{100}-R_{0}}{R_{0} \times 100}$$

(iv) Pyrometers thermometer:
Pyrometers are the instruments which measure the temperature by measuring the intensity of radiations received from the body.

Thermometry and Calorimetry:
The thermometer is a device used to check the temperature of an object. This branch of measurement of the temperature of a substance is called thermometry. It is measured in degrees or Fahrenheit, usually.

Calorimetry also means the measurement of heat but in joules. It states the amount of heat lost by the body is the amount of heat gained by its surrounding.