Question

A constant volume gas thermometer works on:
A.The principle of Archimedes
B.Boyle’s Law
C.Pascal’s Law
D.Gay- Lussac’s Law

Answer 1

Hint:To answer this question, you must recall the ideal gas equation. Also you must recall the gas laws, Archimedes principle and Pascal's Law. The thermometer is based on the fact that at constant volume, pressure is directly proportional to temperature.

Formulae used: $PV = nRT$
Where, $P$ is the pressure exerted by the gas on the walls of the constant volume gas thermometer
$V$ is the total volume occupied by the gas or the volume of the constant volume gas thermometer
$n$ is the number of moles of the gas present in the constant volume gas thermometer
And, $T$ is the temperature at which the gas is present in the constant volume gas thermometer

Complete answer:
A constant volume gas thermometer is composed of a bulb which is filled with a certain amount of a gas, which remains constant throughout. The bulb is further attached to a manometer which is an instrument used to measure the variation in pressure.
We know from the Gay- Lussac’s Law that when volume of a gas is constant, the pressure of the gas is directly proportional to its temperature. As the temperature changes, the pressure changes accordingly and this is how a constant volume gas thermometer measures the increase in temperature.

Thus, the correct answer is D.

Note:
 A gas is defined by four states namely volume, pressure, temperature and the number of moles. The individual relations between these four states are given by the four gas laws as follows:
Boyle’s Law: $P \propto \dfrac{1}{V}$
Charles’ Law: $V \propto \dfrac{1}{T}$
Gay- Lussac’s Law: $P \propto T$
Avogadro’s Law:$V \propto n$
Combining all these individual relations, we obtain a relation as $PV \propto {\text{nT}}$ which holds true for all the gas laws. Adding an equality constant $R$, to remove the proportionality constant, we get the Ideal gas equation.
$PV = nRT$