TEACHERSí NOTES FOR
THE PHOTOELECTRIC EFFECT
VIRTUAL LAB

 
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SAMPLE LESSON PLAN - THE PHENOMENON - PHYSICS APPROXIMATIONS - NOTES - TROUBLESHOOTING

SAMPLE LESSON PLAN
(a 90-minute lesson or two 45-minute periods)

Goals:



Part One: Explanation (5-10 minutes if "readme" file has been read beforehand)

Have your students read the "Studentsí readme file" that is available at this website. Alternately, you might print the text out for them and have them read about the virtual lab in advance. Share with them that they will explore the complexities of the photoelectric effect by choosing just one of four different relationships that are available in the software. Students (or teams of students) are welcome to choose any of the four; variety within the class is a benefit. They may also choose any one of four different test metals to explore.

Part Two: Demonstration(5-10 minutes)

Show your students how to create a graph by doing one sample trial. Carefully avoid any discussion of the physics of the situation; youíll want your students to suggest the physics based on their findings.

Part Three: Application (15-20 minutes)

Have your students choose a metal and a relationship that theyíd like to explore. Then have them pursue that exploration fully. You may want to ask your students to PREDICT the general shape of the graph beforehand, assuming a WAVE MODEL of light. As the activity proceeds, periodically ask your students if their prediction is holding or if theyíll have to adjust their model.

You may want to play "traffic cop" with the printing of graphs; encourage your students to print only when they have fully explored their chosen relationship. Clearly, within the time constraint that you give them, more data is always better than less data.

After exploring for some time, encourage your students to prepare a precise mathematical description of the relationship. If they have time, have them choose a second metal and repeat their tests. Are there any differences that can be gleaned from the graph? (Hint: the answer to this will depend upon the graph.)

Part Four: Evaluation (5-10 minutes depending upon time)

Have each team briefly describe their findings. If this is the end of the first day of a two-day exercise, repeat the findings at the beginning of day two for re-orientation. Summarize the findings on the board or overhead so that students can see the results of the variety of explorations. Be firm about the need for precise language when describing the relationships. The value of a variety of explorations should become apparent at this time.

Part Five: Extension (10-15 minutes)

In small groups, have the students discuss whether or not the wave model can explain the findings on the board. Draw their attention to the "Number of electrons vs. Frequency" graph or the "KE vs. Frequency" graph, if need be. Can a wave model be used to explain threshold frequencies? Why is it that some high intensity waves do NOT liberate any electrons? After some group discussion time, entertain suggestions from each group.

Part Five (optional): Explanation(10 minutes)

If students have not previously been exposed to Planckís quantized energy relation (E = hf), introduce this concept now. If they are already familiar with this idea and it has not come up in the previous discussion, remind students about this quantization and ask if it can be used to explain the data.

Part Six: Application(20-25 minutes)

With Planckís quantization idea now introduced, have ALL students go back to the software and explore the "KE vs. Frequency" graph. It is not necessary to proscribe which metal to use. Indeed, a greater understanding may come out of exploring different metals. Their goal is to produce a graph, find the slope and x-intercept, and interpret the results. The overall question: How does Planckís quantized energy concept fully explain the photoelectric effect? Additional questions: What is the physical significance of the slope? The x-intercept? Why is there a distribution of KE at any given frequency? These questions can be used for further conversation, for an at-home assignment, or as part of a written report about the lab.