In: Physics
Photoelectric Test Question
Here is a set of data from Millikan’s initial photoelectric experiments:
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 wavelengths of light. All light is shown upon the same metal surface. From this data 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, with the light incident upon one metal surface. Draw the potential with the polarity that could stop the photocurrent. How does the stopping voltage stop the photocurrent?
2) Convert the wavelength to frequency (f), then plot the stopping potential energy (e*V0) (on the y-axis) vs. f (on the x-axis). Make your plot large. You can plot eV in either electron-Volts of energy or Joules of energy. Draw a straight line of best fit through the data. The slope of that line is the experimental value for Planck’s constant. Explain why.
3) Extrapolate your straight line by through the y-axis. The y-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?