Photoelectric Effect Activity
Name:
Period:
AP Physics
The ability of some materials to absorb light energy and use it to free electrons that then create a
current is called the photoelectric effect. The details of the photoelectric effect were important in
motivating Einstein to accept and expand Planck’s idea that light is quantized. In this activity we will
look at a simulation of the photoelectric effect and see how the material responds to different light
conditions.
We will use the photoelectric simulation applet found at:
http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm
One note, in this simulation the maximum intensity of the lamp is the same for every lamp.
Procedure
Part A – Intensity vs Current for Different Colors of Light.
1. Make sure that the radio button for cesium is chosen. Set the stopping voltage in the circuit sot that it
is 0.0 V.
2. Set the intensity at the lowest possible value (0%)
3. a. Set the light wavelength for 400 nm.
b. Increase the intensity of the light by 15% and record the amount of current produced.
c. Repeat step b until you reach maximum intensity (100%).
4. a. Reset the intensity at the lowest possible value.
b. Set the light wavelength for 500 nm.
c. Increase the intensity of the light by 15% and record the amount of current produced.
d. Repeat step b until you reach maximum intensity (100%).
5. a. Reset the intensity at the lowest possible value.
b. Set the light wavelength for 600 nm.
c. Increase the intensity of the light by 15% and record the amount of current produced.
d. Repeat step b until you reach maximum intensity (100%).
Wavelength:
Intensity
(%)
Intensity
(W)
Wavelength:
Current
(A)
Intensity
(%)
Intensity
(W)
Wavelength:
Current
(A)
Intensity
(%)
6. Plot all three sets of data on one complete graph and label each by wavelength.
7. How can you explain the difference between the different wavelengths?
Intensity
(W)
Current
(A)
Extension:
1. Set intensity to 50% and set the wavelength to 800 nm. Measure and record the photocurrent
produced
2. Decrease the wavelength by 50 nm. Record the photocurrent produced.
3. Repeat step 2 until you are at the smallest wavelength possible
4. Graph your results
Wavelength (nm)
Intensity (W)
Photocurrent (A)
Part B – Incoming Photons Frequency vs. Kinetic Energy of Ejected Electrons
1. Set the intensity to 50% and leave it there. Move the wavelength to 600 nm
2. a) Set the stopping voltage, V0, to zero.
b) Decrease the wavelength until a small current appears.
c) Increase the stopping voltage, V0, until the current becomes zero. Record the wavelength of the
light and the stopping voltage.
3. a) Reset the stopping voltage to zero then decrease the wavelength still further
b) Increase the stopping voltage, V0, until the current becomes zero. Record the wavelength of the
light and the stopping voltage.
c) Repeat steps a and b for 4 more wavelengths.
Light
Wavelength Frequency Photon
(m)
(Hz)
Energy
(J)
Photon
Energy
(eV)
Photoelectron
Stopping
Maximum
Voltage (V)
Kinetic
Energy (eV)
Work
Function
(eV)
Average 0:
Questions for Part B
1. Graph the maximum kinetic energy of the photoelectron as a function of light frequency and find the
equation for the graph.
2. Calculate the work function for the data in each trial. Then calculate the average value of all your
trials.
3. Compare the equation for your graph to the photoelectric energy conservation equation:
(hf = Kmax + 0). What should the slope of your graph be equal to? Determine the value and
convert it into typical units.
4. Compare the equation for your graph to the photoelectric energy conservation equation:
(hf = Kmax + 0). What should the y-intercept of your graph be equal to? Determine the value
and convert it into typical units.