PART I - The Work Function
• Launch the Photoelectric Effect simulation.
• Increase the intensity to 50%.
At this point, you should notice the ejection of elections from the surface.
• Check the box "electron energy vs. light frequency."
• Use the slider to increase the intensity.
In what way is the current meter an indicator of the number of electrons making it to the positive plate? Does this increase in the intensity of the light beam also increase the number of ejected electrons, or the kinetic energy (speed) of the ejected electrons? Which result is consistent with the photon model of "quantized energy packets"?
• Increase the wavelength of the light until electrons are no longer ejected.
Recall that increasing the wavelength decreases the frequency of the light. Record your observations in your laboratory notebook. Answer the following questions in your notebook: What is the relationship between the energy of a photon and its frequency? Sketch a graph of photonic energy versus frequency. Does wavelength or intensity determine whether electrons are ejected from the surface?
In your laboratory notebook record the wavelength (λ) in the table below and complete the calculations. The frequency ƒ can be
calculated as ƒ = c/λ, where c is the speed of light, approximately 3 x 1017 nm/s.
The energy of the photon can be calculated from the formula E = hƒ, where
Planck's constant (h) = 6.6 x 10-32 J s
Your energies will initially be given in units of joules, so in order to compare to published lists of work function values-that are in electron volts-your final value will require conversion into this unit. The conversion between electron volts and joules is
1 eV = 1.6 x 10-19 J
• Repeat the above step for each of the metals under the pull down menu.
Metal Wavelength
(λ) (nm) Frequency
(Hz) Work Function
(J) Work Function
(eV)
Sodium
Zinc
Copper
Platinum
Calcium
Unknown
Part II - The Number of Ejected Electrons
• Check the box "current vs light intensity."
• Select the metal platinum.
• Adjust the frequency of the incident light slightly above the threshold frequency.
• Vary the intensity of the light, and observe any changes in the number of ejected electrons.
• Increase the frequency of the incident light until it is well above the threshold frequency.
• Vary the intensity of the light, and observe any changes in the number of ejected electrons.
Record your observations and answer the following questions in your laboratory notebook:
1. What's the relationship between the frequency of the incident light, the threshold frequency, and the number and energy of the ejected of electrons?
2. What's the relationship between the intensity of the incident light, the threshold frequency, and the number and energy of the ejected of electrons?