Lesson: Heat Engines Physics • 9th Grade

In this lesson, we will learn how to compare the work done by heat engines with different reservoir temperature ratios and how to calculate their efficiencies.

Lesson Plan

Students will be able to

recall that the work done by a heat engine is determined by subtracting the heating of its low-temperature reservoir from the cooling of its high-temperature reservoir,
qualitatively describe efficiencies of heat engines from graphs showing the changes of temperature of the reservoirs of a heat engine with time,
recall that the equation efficiency = applies to an ideal heat engine for which there is a negligible change of reservoir temperatures,
use the equation efficiency = in all combinations,
identify the work done and the heating and cooling occurring during the adiabatic changes and isothermal changes that occur over a Carnot cycle.

Lesson Worksheet

Q1:

What is the efficiency of a heat engine that has constant reservoir temperatures of and ? Give your answer to three decimal places.

Q2:

The graph shows the relationship between the loss of the internal energy of the high-temperature reservoir of a heat engine and the gain in internal energy of the heat engine’s low-temperature reservoir for different values of , the ratio of the temperatures of the reservoirs. Which is the greatest temperature ratio?

Q3:

A heat engine is represented in the diagram, showing the quantities associated with its operation. Which of the following formulas most correctly represents the relationship between , , and ?