Thermal Efficiency of a heat engine

Ø    It is very obvious that higher the conversion of heat energy to mechanical energy by an engine, the higher its efficiency.

Ø   Let Q₁ = heat absorbed by an engine

          Q₂ = unutilized heat, i.e rejected heat

Then efficiency of heat engine is defined as,

η =        heat supplied – heat rejected

                               heat supplied

   =         converted heat

             heat supplied

  

   =       Q₁ – Q₂

                 Q₁

                 

   =          1 – Q₂

Q₁