iSES - Internet School Experimental System

Photoelectric effect

Assignment

1. Run the remote experiment ‘Photoelectric Effect’.
2. Try to predict whether you will observe any photocurrent with the shielded phototube. You may appreciate to see the scheme of the circuit (in the fig. 1 or 5). For the verification, in the left panel: Switch the mercury lamp ON and switch the LED 940 nm OFF. In the right panel: Select the filter position F6. When ready, press the ‘AUTO’ button to start the automatized scan.
3. Keep the filter position F6, switch the LED 940 nm ON and press the ‘AUTO’ button again, and perhaps the ‘Clear graph’ button. Try to predict whether some photocurrent appears when the photocathode is lit.
4. Measure more volt-ampere characteristics for the other wavelengths – filter positions F1–F5 (without clearing the graph and with the use of the ‘AUTO’ button as recommended for smoother curves). Describe the differences and the kind of dependence on the wavelength.
5. Explain the stopping voltage method and how we can read the stopping voltage from the V-A characteristics?
6. Record your measurements of V-A characteristics for selected wavelengths for further process to determine the stopping voltage values U₀(λ).
7. Calculate the corresponding frequencies f and plot the dependences U₀(λ) and U₀(f).
8. Determine your experimental values of the Planck constant and the work function, with errors of the results.
9. Discuss your results and compare them to the literature value.

1. Study the theory and run the remote experiment ‘Photoelectric Effect’.
2. Measure the leakage current and determine the offset of the y-axis. (Switch the mercury lamp ON, switch the LED 940 nm OFF, select the highest amplification and select the filter position F6. We recommend to uncheck ‘Keep exp. ID’. You should use the ‘AUTO’ button and the ‘START/STOP Recording’ buttons.)
3. You may keep the filter position F6 and switch the LED 940 nm ON to verify whether some photocurrent appears for the wavelength 940 nm incident onto the photocathode.
4. Measure the volt-ampere characteristics for all wavelengths – filter positions F1–F5 (with the use of the ‘AUTO’ button as recommended for smoother curves). Describe the differences and the kind of dependence on the wavelength.
5. Record your measurements of V-A characteristics (with the noise) for the further process to determine the stopping voltage values U₀(λ). Try to use more advanced methods of graphical data processing and perhaps consider corrections of the offset and the leakage current.
6. Plot the dependence U₀(f) with the model function (theoretical fit).
7. Determine your experimental values of the Planck constant and the work function, with errors of the results.
8. Discuss your results and compare them to the literature value.

For more details please read User's Manual.