PhET Simulation: Photoelectric EffectName: ______

Determination of how different variables affect the current generated by the photoelectric effect.

Instructions:

  • Google “Phet Photoelectric Effect” and click on the link to the simulation. It’s a Java simulation that you’ll need to be able to run in order to complete this activity
  • Get the simulation ready by clicking the following settings:
  • Set the Target to “?????”
  • Check on “show only highest energy electrons”
  • Make sure voltage and intensity are both starting at 0 (you’ll modify these later)
  • Note: You may manually change the wavelength and the intensity by dragging the slider bars, or you can click in the number box and type in a specific value.
  • Type your answers into this document, and insert an image of your graph when requested in the questions.

Turning this work in:

  • Save your document as a pdf when you are completely done with all the parts.
  • upload the pdf to in order to earn credit for this activity. You will earn up to 20 points, depending on the completion and quality of your answers.
  • Complete the post-lab WebAssign, which is able to earn you up to 10 points.
  • Please have all parts done and submitted no later than Wednesday, May 30, 2018.

Part 1: Intensity’s effect on the current

  1. Set the wavelength to exactly 400 nm and leave the external voltage at 0.00 V. Record the current for at least 10 different intensities greater than 11%. Use the entire range of intensities from 11 – 100%.

Light Intensity / ± 1% / Current / ±0.001 A
Trial 1 / Trial 2 / Trial 3 / Trial 4 / Trial 5
  1. Calculate the average current for each measured intensity

Light Intensity / ± 1% / Average Current / A / Current Uncertainty / A
  1. Using LoggerPro, create a graph of the effect of intensity on the resulting current, including error bars. Copy and paste a copy of your graph here:
  1. What does your graph tell you about the relationship between light intensity and current for a wavelength of 400 nm?
  1. What would explain this relationship?

Part 2: Wavelength and its effect on current produced

  1. Set the light intensity to 100%, and leave the external voltage at 0.00 V, keeping both constant for the duration of this section. Record the current for at least 10 different wavelengthsthroughout the range of the EM spectrum, but at least 7 of your data points must generate a measureable current.

Wavelength / ± 1 nm / Current / ±0.001 A
Trial 1 / Trial 2 / Trial 3 / Trial 4 / Trial 5
  1. Calculate the average current for each measured wavelength

Wavelength / ± 1 nm / Average Current / A / Current Uncertainty / A
  1. Create a graph of the effect of wavelength on the resulting current. If anything generated 0.000A of current, do not include the data for the best-fit line. Copy and paste a copy of your graph here:
  1. According to your graph, what is the first wavelength that would generate a current?
  1. According to the simulation, at what incident wavelength will electrons first be ejected from the surface? At what wavelength will there first be a measurable current?
  1. How does your graph result compare to the simulation result?

Part 3: Effect of frequency on the energy of the ejected electrons

Your data collected for this part will begin with the wavelength for which you first get a measurable current. To determine the energy of the electron, we need to adjust the battery until its voltage first stops the electrons from generating a current. In other words, as you watch the electrons move toward the plate on the right, we want to “charge” that plate with the battery so that the electrons JUST reach it before being pushed back to their original plate. Once you get that set up correctly (and remember you should be looking at only the highest energy electrons), you’ll record the voltage from the battery. The voltage from the battery is equivalent to the energy of the electrons in eV (because it’s work done to the electron to bring it briefly to a stop).

  1. Starting with the wavelength for which you first get a measurable current, record the energy of the electrons ejected from the surface. Use at least 8 completely different wavelengths over a suitable range of values

Wavelength / nm / Electron Energy / eV
  1. Calculate the frequency of the light:

Frequency / Hz / Electron Energy / eV
  1. Create a graph showing the effect frequency has on the energy of the electron. Insert the graph here:
  1. What is the slope of your line (including units)? What is your slope supposed to be?
  1. What is the y-intercept of your line? What is the x-intercept of your line? What might be the importance of either of these values?