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Transcript
Physics Unit 7: Quantum Physics T4. Photoelectric Effect
TEACHER PAGE
Photoelectric Effect Lab
TEKS
(8) Science concepts. The student knows simple examples of atomic, nuclear, and quantum phenomena. The student
is expected to:
(A) describe the photoelectric effect and the dual nature of light
Purpose & Student Outcomes
Students will explore the photoelectric effect.
Students will hypothesize about the presence of the threshold frequency.
Materials
1 strip of poster board
Masking tape
3 marbles
1 styrofoam cup
1 popsicle stick
1 ruler
Instructions for teacher
Pre-lab
1. Distribute Photoelectric Effect Lab Student Page to each student at least one day in advance.
2. Instruct students to complete Pre-lab in the lab notebook prior to the date of the lab. Pre-lab includes:
 Background questions
 Safety
 Purpose
 Procedure
 Hypothesis
 Data and observations table
Lab Set-up
1. Cut strips of poster board with an approximate 4” width.
2. You could build an example setup at the teacher station prior to them starting the lab.
Background info:
The photoelectric effect is the emission of electrons when electromagnetic radiation falls on
an object. It was first theorized by a German physicist named Max Planck and later
expanded upon by Albert Einstein. Light consists of discrete bundles of energy called photons. The amount of energy
in a photon varies depending on the wavelength/frequency of the light. Thus different colors of light provide
different amounts of energy. When there is a sufficient amount of energy to break the bonds, an electron is ejected.
If the energy transferred by the photon is not high enough to eject the electron, we say that is has not reached the
threshold. The threshold is different for different materials. Thus, yellow light may be able to cause a photoelectric
effect in cesium, but unable to cause it in zinc.
Post-lab
1. Write and answer any post lab questions that pertain to the lab.
2. Have students write a conclusion showing mastery of the subject matter. You may choose to take out the
instructions for the conclusion if you already have a standard set up.
Things that they should include in their conclusions:
a. Definitions of photoelectric effect and threshold frequency.
b. Correlate energy to color
c. Color(s) which caused the emission of the electron
d. Some materials hold their valence electrons tighter than
others. Describe how the model could be modified to show
this.
e. Photographers often have red lights in their darkrooms.
Explain why they use red light but not blue light.
Physics Unit 7: Quantum Physics T4. Photoelectric Effect
STUDENT PAGE
Photoelectric Effect Model and Simulation
Background questions:
What is the photoelectric effect?
Who first theorized the photoelectric effect?
What are photons?
To which wave property does the energy in a photon relate?
When is an electron ejected?
What is the threshold frequency?
Is the threshold frequency constant or does it vary with different materials?
Materials:
1 Strip of posterboard
1 styrofoam cup
Masking tape
1 popsicle stick
3 marbles
1 ruler
Procedure:
Part I: setup
1. fold the posterboard in half lengthwise
2. make a cut 3.5 cm from the end that does NOT completely cut through
3. make a second cut 3.0 cm above the first cut that does NOT completely cut through
4. 13 cm above the second cut, draw a line and label it red
5. 5 cm above that mark, draw a second line and label it orange.
6. repeat step 5 four more times labeling them yellow, green, blue, and violet in that order
7. Next, poke the Popsicle stick through the base of the cup.
8. Set the cup on the desk and slide the Popsicle stick up so that the top is at a height of 15 cm. Tape the
Popsicle stick in this position.
9. Tape the “violet” end of the posterboard to the top of the Popsicle stick.
10. Bend the posterboard at the second cut so that the rest sits level on the desk. Tape into this position
11. Bend the posterboard at the first cut so that the end of the posterboard is 1.5 cm off the desk. Tape
the cut into this position.
Part II:
1. Place two marbles in the lowest point of the slide so that they are touching. These two marbles
represent two valence electrons in the atom.
2. Place the third marble at the position labeled red and release the marble. This represents a photon of
red light.
3. Repeat steps 1-2 for each colors’ mark on the slide.
4. Observe the effect on the marbles and record your results.
RISD Curriculum & Instruction
Physics Unit 7: Quantum Physics T4. Photoelectric Effect
STUDENT PAGE
Diagram: Draw a diagram of the setup in your lab notebook.
Hypothesis:
Data Collection: Create a table to record your observations.
Conclusion:
 Definitions of photoelectric effect and threshold frequency.
 Correlate energy to color
 Color(s) which caused the emission of the electron
 Some materials hold their valence electrons tighter than others. Describe how the model could be
modified to show this.
 Photographers often have red lights in their darkrooms. Explain why they use red light but not blue
light.
RISD Curriculum & Instruction