## Conceptual Physics (12th Edition)

As discussed on page 345, Carnot's equation states that the ideal efficiency of a heat engine is $\frac{T_{hot} – T_{cold}}{T_{hot}}$. Mathematically speaking, lowering the temperature of the cold reservoir allows the engine to be more efficient. This is easier to see when Carnot's equation is re-written as $efficiency_{ideal} = 1 - \frac{T_{cold}}{T_{hot}}$.