How is the thermal efficiency of a heat engine defined? how is the thermal efficiency of a heat engine defined? the efficiency is defined as the ratio between the work performed and the heat output at the lower temperature. the efficiency is defined as the ratio between the heat output at the lower temperature and the heat input at the higher temperature. the efficiency is defined as the ratio between the work performed and the heat input at the higher temperature. the efficiency is defined as the ratio between the heat input at the higher temperature and the heat output at the lower temperature.

The efficiency is  define as the ratio between the work performed and the heat input at the higher temperature

Explanation:

The efficiency of the heat engine work done using working substance at higher temperature relates to the wasted energy released to the environment through the derived formula below:

Qin = quantity of heat from a working substance such steam or water used to drive electric generator at higher temperature for example

Qout = quantity of heat remaining in the working substance after the work has been done

Qin = Wout + Qout where Wout is the significant work that the higher temperature working substance has been used to do

Wout = Qin - Qout

efficiency = Wout / Qin =  ( Qin - Qout) / Qin = Qin / Qin - Qout / Qin = 1 - (Qout / Qin) and

Carnot theorem relates the efficiency with the formula below:

eff( max) = 1 - ( Tc/Th) where Tc is the temperature of the cold reservoir where the working substance is poured and Th is the temperature of the working substance before it input into the thermal engine.