When we talk about how well a refrigerator works, we often use a special term called the Coefficient of Performance (COP).

You can think of it like this:

$COP = \frac{Q_c}{W}$

Here’s what that means:

• $Q_c$ is the amount of heat the refrigerator takes away from inside (the cold part).
• $W$ is the energy (or work) that goes into making the refrigerator run.

Now, for heat engines, which are different from refrigerators, we look at how efficient they are using another term called efficiency, or η.

It can be shown like this:

$\eta = \frac{W}{Q_h}$

In this case:

• $W$ is the work done by the engine.
• $Q_h$ is the heat that the engine gets from outside.

One of the tricky parts about measuring how well refrigerators and engines work is that there are challenges in getting accurate numbers.

In the real world, calculating the exact values and understanding energy lost during the process can be complicated.

To make sure we get the right answers, it's really important to set up good experiments and take accurate measurements.