Photoelectric Test Question
Here is a set of data from Millikan’s initial photoelectricexperiments:
Wavelength (nm) Stopping Potential (Volts)
254nm 2.57V
313nm 1.67V
365nm 1.09V
405nm 0.73V
434nm 0.55V
V0 is the stopping voltage for each of the incident wavelengthsof light. All light is shown upon the same metal surface. From thisdata we can determine an experimental value for Planck’s constant(h) and the work function of the metal (Φ).
1) Draw the circuit diagram for the photoelectric effect, withthe light incident upon one metal surface. Draw the potential withthe polarity that could stop the photocurrent. How does thestopping voltage stop the photocurrent?
2) Convert the wavelength to frequency (f), then plot thestopping potential energy (e*V0) (on the y-axis) vs. f (on thex-axis). Make your plot large. You can plot eV in eitherelectron-Volts of energy or Joules of energy. Draw a straight lineof best fit through the data. The slope of that line is theexperimental value for Planck’s constant. Explain why.
3) Extrapolate your straight line by through the y-axis. They-intercept of your straight line is the work function of the metal(Φ). Explain why this is the case. What is the value you obtain?What metal do you think this is?
