Thermometer And Its Types - Practice Questions & MCQ

Thermometry: A branch of science that deals with the measurement of the temperature of a substance is known as thermometry.

An instrument used to measure the temperature of a body is called a Thermometer. The principle on which it works is by absorbing heat from the body.

There are various kinds of thermometers which are briefly classified in three types - 

• Liquid thermometers - In liquid thermometers, mercury is usually preferred over other liquids. The reason behind this is its expansion is large and uniform. And the main reason behind all these is that it has high thermal conductivity and low specific heat.

Range of temperature :(freezing point of mercury) - ( boiling point of mercury) which is $-50^{\circ} \mathrm{C}$ to $350^{\circ} \mathrm{C}$

The formula for calculation of temperature at any length I:

$
t=\frac{l-l_0}{l_{100}-l_0} \times 100^0 \mathrm{C}
$

Here $-l=$ length of the mercury column at the given temperature $t$.
$l_{0=}=$ length of the mercury column at the $0^{\circ} \mathrm{C}$ temperature
$l_{100}=$ length of the mercury column at the $100^{\circ} \mathrm{C}$ temperature
- Gas thermometers : In this gases are used as thermometric material. Gas thermometers are more sensitive and accurate than liquid thermometers as the expansion of gases is more than that of liquids. In this gas are used as a thermoelectric substances are called ideal gas thermometers.
These are basically of two types
(i) Constant pressure gas thermometers - If pressure is constant, then for ideal gas, volume is directly proportional to temperature. So, $V \alpha T$

The formula for calculation of temperature at any volume V : $t=\frac{V-V_0}{V_{100}-V_0} \times 100^0 \mathrm{C}$

Here, $V=$ volume of the gas column at the given temperature $t$.
$V_0=$ volume of the gas column at the $0^{\circ} \mathrm{C}$ temperature.
$V_{100}=$ volume of the gas column at the $100^{\circ} \mathrm{C}$ temperature.
(i) Constant volume gas thermometers - If the volume is constant, then for an ideal gas, pressure is directly proportional to temperature. So, P $\alpha$

The formula for calculation of temperature at any pressure $\mathrm{P}: t=\frac{P-P_0}{P_{100}-P_0} \times 100^0 \mathrm{C}$
Here, $P=$ pressure of the gas column at the given temperature $t$.
$P_0=$ pressure of the gas column at the $0^{\circ} \mathrm{C}$ temperature.
$P_{100}=$ pressure of the gas column at the $100^{\circ} \mathrm{C}$ temperature.
- Resistance thermometers: Usually Platinum, Germanium is used in resistance thermometers due to high melting point and large value of temperature coefficient of resistance. This type of thermometer can be used for high temperatures.

The formula for calculation of temperature at any resistance R :

$
t=\frac{R-R_0}{R_{100}-R_0} \times 100^0 \mathrm{C}
$

Here, $R=$ Resistance of the material at the given temperature $t$.
$R_{0=\text { Resistance of the material column at the } 0^{\circ} \mathrm{C} \text { temperature. }}$.
$R_{100}=$ Resistance of the material column at the $100^{\circ} \mathrm{C}$ temperature.