Carnot's Cycle FIGURE 20-5 The Carnot cycle Heat In a cyo the cycle for the Carnot engine begins at point expansion diagram (1)The gas is first panded isothermally, with addition of heat QH, along the path ab at temperature TH. (2)Next d→ the gas expands adiabatically Adiabatic Adiabatic from b to c-no heat is exchanged, compression lexpansion but the temperature drops to TL (3) B)The gas is then compressed at co stant temperature Ti, path c to d 0=0 and heat e. flows out. (4)Finally the gas is compressed adiabatically. path da, back to its original state. No Carnot engine actually exists, but as a theoretical engine it played c→d Isothermal Important role in the development of thermodynamics compressionCarnot’s Cycle