Activity Description

This activity makes use of the Photoelectric Effect Simulation on the PhET wbsite. The linked multiple choice questions ask a series of comparisons between the classical and quantum predictions of the photoelectric effect. The simulation is used to demonstrate the experimentally observed behavior.

Target Conceptual Difficulty

Student difficulty in distinguishing between the classical and quantum preedictions of the photoelectric effect.

PowerPoint

LMC - Photoelectric Effect (TurningPoint)

LMC - Photoelectric Effect (iClicker)

Simulation

http://phet.colorado.edu/en/simulation/photoelectric

Click on the Play with Sims button. Click on the link in the Left Frame for Quantum Phenomena, then click on the icon for Photoelectric Effect. Click on the Run Now button to start the simulation.

Presentation Notes

I use sodium as the photocathode for all questions with the reatarding potential set to 0 V. I initially set up the simulation with infrared light with about 50% intensity. I increase the intensity to demonstrate the first two questions. I then move the light to the UV again at agout 50% intensity to demonstrate the next two questions. Sodium has a threshold wavelength in the simulation at about 540 nm. I use a little less than 540 nm initially for the last two questions and then increase the wavelength by about 10 nm.

Student Results

The distractors for the linked multiple choice questions on the photoelectric effect are listed below. Note for the iClicker version the distractor 6. Cannot be determined is not used.

1. photocurrent increases immediately
2. photocurrent increases gradually
3. photocurrent decreases immediately
4. photocurrent decreases gradually
5. No change in the photo current
6. Cannot be determined

Students showed definite difficulties in distinguishing between effects that were small but immediate and effects that were gradual.
1.) Infrared light shined on the photocathode initially emits no electrons. The intensity of the light is increased. The classical prediction is
Responses (percent) (count)
1 22.22% 4
2 72.22% 13
3 0% 0
4 0% 0
5 5.56% 1
6 0% 0
Totals 100% 18

2.) Infrared light shined on the photocathode initially emits no electrons. The intensity of the light is increased. The quantum prediction is
Responses (percent) (count)
1 50% 9
2 0% 0
3 0% 0
4 0% 0
5 50% 9
6 0% 0
Totals 100% 18

3.) Ultraviolet light shined on the photocathode initially emits electrons. The intensity of the light is increased. The classical prediction is
Responses (percent) (count)
1 11.11% 2
2 88.89% 16
3 0% 0
4 0% 0
5 0% 0
6 0% 0
Totals 100% 18

4.) Ultraviolet light shined on the photocathode initially emits electrons. The intensity of the light is increased. The quantum prediction is
Responses (percent) (count)
1 88.24% 15
2 0% 0
3 0% 0
4 0% 0
5 11.76% 2
6 0% 0
Totals 100% 17

5.) It is observed that light of 430 nm just begins to emit photoelectrons. The wavelength of the incident light is changed to 440 nm. The classical prediction is
Responses (percent) (count)
1 0% 0
2 27.78% 5
3 0% 0
4 5.56% 1
5 66.67% 12
6 0% 0
Totals 100% 18

6.) It is observed that light of 430 nm just begins to emit photoelectrons. The wavelength of the incident light is changed to 440 nm. The quantum prediction is
Responses (percent) (count)
1 44.44% 8
2 16.67% 3
3 22.22% 4
4 5.56% 1
5 5.56% 1
6 5.56% 1
Totals 100% 18

Pen and Paper Actvivities

Pen and Paper version of this activty

Follow up tipers from homework assignments, test reviews and test items