### Welcome to Lesson 3!

Alright, we are into lesson 3. Lesson 3 basically deals with energy efficiency. Upon completing this lesson, you will really get a quantitative feel for what energy efficiency is and also how to calculate energy efficiency with a conversion device. A conversion device can be anything – an automobile or a power plant or any device that converts one form of energy to another form.

And we will also understand the concept of entropy. Entropy is disorder. Because of entropy, our efficiencies are lower than what we normally expect. And we will look at the operating principle of a heat engine. A heat engine is a device that converts heat to work. Particularly, automobiles are all heat engines and they are notoriously inefficient. We will see 2 examples, and calculations of why these automobiles are notoriously inefficient.

We can also calculate the efficiency of a whole process from the step efficiencies. For example, if it involves 2 or 3 steps like in a relay race. You know you have 3 or 4 players taking the baton and one lap by each of the athletes. So, what is the overall or team efficiency if we know the efficiency of each of those steps or the efficiency of each of those players? That is a very important concept in this chapter.

While doing this, we will also learn about temperature scales; Kelvin scale, Fahrenheit, and also Celsius. So there will be a lot of numerical problems in this lesson.

Alright! Good luck!

#### Lesson 3 Objectives

Upon completing this lesson, you should be able to:

- define and calculate efficiency of an energy conversion device;
- articulate the concept of entropy;
- explain operating principles of a heat engine; and
- calculate overall efficiency from step efficiencies.

**See the calendar in Canvas for due dates/times.**

#### Questions?

If you have any questions, please post them to the **General Course Questions** forum in located in the Discussions tab in Canvas. I will check that discussion forum daily to respond. While you are visiting the discussion board, feel free to post your own responses to questions posted by others - this way, you might help a classmate!