Photoelectric Effect Lab Activity 2: Photocircuit Experiment 8. Switch the metal to zinc. O Online Instructions 9. Find the threshold frequency for zinc using the same method in steps 4 and 5. OBJECTIVE Question 7: What is the threshold frequency for zinc? Show your calculations. To investigate the nature of the photoelectric effect and determine the work function of an unknown metal. Question 8: What is the work function for zinc? Show your calculations. OVERVIEW 10. From the "threshold frequency arrangement," set the wavelength to a smaller value by no fewer than 20 nm and no more than 40 nm. Looking back at the two models for light that have been discussed so far, the wave model and the ray model, or particle model. Both have been valuable in explaining certain light phenomenon from diffraction to image forming. However, Question 9: What is this new wavelength? there lies the question whether light was a particle or a wave. This was finally resolved by the development of the 11. Adjust the stopping potential of the battery so that it just barely stops the current. Notice the there are two photon model; light is a small wave packet. This model helped Einstein's explanation of the photoelectric effect. When methods for adjusting the potential. Use the method that allows for greater precision. When the condition is light shines on a metal surface, electrons can be ejected from the metal. This could not be fully explained by the wave or met, electrons are ejected from the zinc and almost make it to the opposite electrode. But they return to the the particle but can be explained with this new model. Photons travel at the speed of light, the speed of the photon is zinc, and the current remains zero. related by the wavelength and frequency. Question 10: Record the minimum stopping potential for this wavelength in volts. c = fx 12. Repeat the process of reducing the wavelength by 20-40 nm and changing the stopping potential. Repeat the The energy of the traveling photon is given as process until you have 4 data sets of wavelengths and stopping potential. E = hf Question 11: Make a table of your data. Which h is the Planck's constant, h = 6.62607004 x 10-34 m kg/s. Question 12: Make a graph of your table using a spreadsheet program like Excel or Google Spreadsheets or something else. Include the wavelength 1, stopping potential , incident photon energy E, and ejected photoelectron energy KE. Activity 1: Exploration Open the simulation "Photoelectric Effect" (Website: https://phet.colorado.edu/en/simulation/photoelectric]. Question 13: What is the equation for photon energy? Set the metal to Sodium and the wavelength to 400 nm. In the simulation window's Options menu, select "Show Question 14: What is the equation for the kinetic energy of the photoelectron? photons"- m Slowly move the intensity slider from 0% to 100% and observe the photoelectric effect. The electrons emitted Question 15: Make a graph of photoelectron energy vs. incident light frequency. from the metal are called "photoelectrons". They have the same mass and charge as any other electron. 4. Move the wavelength selector back and forth and observe the results. Try changing the intensity at various Question 16: How can the graph be used to determine the value of the work function? wavelengths to see what effect that has. Question 17: What is the slope of the plotted data? What is the value (including units), and what does it represent? 5. By sliding the wavelength selector back and forth find the threshold wavelength for sodium. Activity 3: A new material Question 1: What is the wavelength of the lowest energy light at which electrons are emitted? This is your threshold 13. Change the material to the unknown metal labeled "??????". wavelength. Question 18: Describe how you could determine the unknown metal using the simulation. Question 2: Use the threshold wavelength to calculate the threshold frequency using equation 1. Show all your work. Question 19: Record your data and determine the unknown metal. Show all calculations. Question 3: Use your textbook to define the work function. What is the definition of the work function? Question 4: Use the threshold frequency to calculate the work function of Sodium using equation 2. Show all your work. 6. Set the wavelength to 400 nm and intensity to 100%. Notice the value of the current in the circuit. Adjust the setting on the battery to cut off the current. That is, when the voltage of the battery causes the current to just barely be brought to zero. Question 5: What is the cut-off potential at 400 nm in volts? 7. Change the wavelength by 100 nm in such a way that current again flows. Question 6: What is the wavelength that allowed current to flow again
