Carnot Efficiency: The Ceiling on a Heat Engine

Heat leaves a hot reservoir, an engine takes a share of it as work, and the rest is dumped into a cold one. The share it can take is fixed by the two temperatures alone: eta = 1 - Tc ÷ Th. Drag the sliders and watch the gold work band widen and narrow.

Carnot efficiency eta = 1 - Tc ÷ Th

50.0%

1 - 300 ÷ 600

Work out W (J)

1,200

Waste heat Qc (J)

1,200

At max power (%)

29.3

Heat-pump COP

2.00

Hot reservoir Th600 K

Cold reservoir Tc300 K

Heat in Qh2,400 J

Reversible engine · one cycle · an upper bound, not a prediction · the cold reservoir can never come within 10 K of the hot one.

Tip: drop Tc by 50 K, hit Reset, then raise Th by 50 K instead. The gold band widens more the first time. The cold side has the greater leverage, which is the thing most people get backwards.