# Won't gas thermometers break on using fixed volume of gas?

From the ideal gas equation, PV is proportional to T. Now if V is kept constant, we'll get Gay-Lussac's law.

Now my question is:

According to observations, we know that substances undergo a change in dimensions or they expand on exposure to heat. So wouldn't that mean the fixed volume of gas must expand on exposure to heat? But if this happens the pressure must also increase, and wouldn't that break the glass thermometer?

• There is no "must". The gas will want to expand, that's right. But whether we let that happen or not is another question. – Ivan Neretin Jan 10 '18 at 6:21
• When a basketball is inflated, pressure increases and it must be accompanied by volume decrease right?. The volume is the space occupied by the molecules of the gas and it's increasing as the no.of molecules of gas pumped into the body increases? – susan J Jan 10 '18 at 6:43