Thermal Physics gets a bit of a bad rap with teachers and students alike. I'm a bit sick of hearing "Thermodynamics… uggghhhh!" Thermodynamics is the science of how heat moves, and it can explain so much of the universe, not to mention being incredibly useful. Without the study of thermodynamics there would never have been steam engines, nor motor cars, and forget keeping your beer cold in the fridge... what a sad world it would be indeed. Thermodynamics may be the reason for the Universe being here at all or it may be the reason life exists at all... fascinating!
The best bit about Thermal Physics though is the experiments that you can do. The three gas laws combine into the ideal gas equation, and two of them are proportional relationships with temperature. As you'll know proportional relationships imply that the trend starts from the origin… so you can reconstruct Kelvin's experiment and extrapolate back to the point where a gas would occupy zero volume, or be at zero pressure. That point would be absolute zero; zero degrees kelvin or -273 degrees Celsius. The coldest anything can theoretically be.
If you can't get excited about that then you may have picked the wrong A Level!