Please watch the 5:30 Lesson 3 Review below:
Review Sheet Lesson 3 – Energy Efficiency
- Energy Conversion
- All the energy that we put in may not come out in the desired form
- Efficiency = Useful Energy Output / Total Energy Input
- Both energies must in the same units
- The temperature of a substance is not a measure of its heat content, but rather, the average kinetic energy of its molecules resulting from their motions
- Heat Engine
- Device that converts Thermal energy into Mechanical energy
- Carnot Efficiency
- All temperatures must be in Kelvin
- As Tlow decreases, efficiency increases. As Tlow increases, efficiency decreases
- As Thot decreases, efficiency decreases. As Thot increases, efficiency increases
- Workings of a Power plant
- Overall Efficiency = product of step efficiencies
The questions below are your chance to test and practice your understanding of the content covered in this lesson. In other words, you should be able to answer the following questions if you know the material that was just covered! If you have problems with any of the items, feel free to post your question on the unit message board so your classmates, and/or your instructor, can help you out!
- A heat engine has Carnot efficiency of 30%. Useful output from the engine is 1000J. How much heat is wasted?
- How can we improve the Carnot efficiency of a heat engine by changing the hot and cold reservoir temperatures?
- Most of the energy conversion devices that we use in our day-to-day life can be classified as Heat Engines. Give two examples.
- The following diagram shows the energy flow to and from a furnace. Calculate the efficiency of the furnace. Show your work very clearly.
For more information on topics discussed in Lesson 3, see these selected References:
- Hinrichs, R. A., “Energy,” Saunders College Publishers, Philadelphia, PA, 1992.
- Aubrecht, G. L., “Energy,” Prentice Hall, Inc., Englewood Cliffs, NJ, 1995.
- Fay, J.A. and Golomb, D. S., “Energy and the Environment,” Oxford University Press, New York, NY, 2002.
- Christensen, J. W., “Global Science: Energy Resources Environment."