Physics (AS & A Level) · Oct / Nov 2016 · Paper 13 · Question 18

An engine transforms thermal energy into mechanical work. The engine takes in thermal energy Q_in from a heat source and gives out thermal energy Q_out to a heat sink, producing useful work W. What is the efficiency of this engine?

1. A\frac{W}{Q_{in} + Q_{out}}
2. B\frac{W}{Q_{in} - Q_{out}}
3. C\frac{W}{Q_{in}}
4. D\frac{W}{Q_{out}}

As printed in the paper