Which ideal gas law does a constant volume thermometer work on? I searches online for my question and found mixed answers. I think the Ans. Should be Gay Lussac's Law as we are dealing with a case of constant volume but variable pressure and temperature. In many books the answer is given to be Charles Law. Would appreciate if someone gave me the ans. Thanks.
Gay-Lussac's Pressure Temperature Law.

The law simply states


  The pressure of a gas of fixed mass and fixed volume, is directly proportional to the gas's absolute temperature.


As telling temperature rises, the gas in the thermometer has its pressure increased in accordance with the law. Measuring this pressure gives us the temperature as per the ideal gas equation, or by using Gay-Lussac's law directly, taking the pressure ratio against a set base temperature and pressure.