What is the formula for calculating the efficiency of a heat engine?

The correct answer is .

Explanation:

Heat engine: It is a device which converts the heat energy in to the mechanical work. In heat engine, the heat is transferred from high temperature reservoir to the low temperature reservoir.

It is just opposite of the refrigeration.

The expression of the work done is as follows;

Here, is the heat added to the system and is the heat rejected to the cold reservoir.

The formula for calculating the efficiency of a heat engine is as follows;

Here, W is the work done and is the heat added from the reservoir which is at high temperature and is the heat rejected to the reservoir which is at low temperature.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.