Photoelectric effect

Photoelectric effect

Procedures

Measuring Planck's constant

Initial configuration

1. Cover the window of the Mercury Light Source Enclosure with the Mercury Lamp Cap. Cover the window of the Photodiode enclosure with the Photodiode Cap.
2. Adjust the distance between the Mercury Light Source enclosure and Photodiode enclosure so that the general spacing is between 30.0 cm to 40.0 cm. NOTE: The recommended distance is 35.0 cm.
3. On the Mercury Lamp Power Supply, press the button to turn on MERCURY LAMP. On the Tunable DC (Constant Voltage) Power Supply and DC Current Amplifier, push in the POWER button to the ON position.
4. Allow the light source and the apparatus to warm up for 10 minutes.
5. On the Tunable DC (Constant Voltage) Power Supply, set the Voltage Range switch to

$-4.5\,\mathrm{V}$ – $0\,\mathrm{V}$. On the DC Current Amplifier, turn the CURRENT RANGES switch to $10$-$13\,\mathrm{A}$.

1. On the DC Current Amplifier, push in the SIGNAL button to the “in” position for CALIBRATION.
2. Adjust the CURRENT RANGES knob until the ammeter shows that the current is zero.
3. Press the SIGNAL button so it moves to the “out” position for MEASURE.

Measurements

1. Gently pull the aperture dial away from the case of the Photodiode Enclosure and rotate the dial so that the 4 mm diameter aperture is aligned with the white line. Then rotate the filter wheel until the 365 nm filter is aligned with the white line. Finally, remove the cover cap.
2. Uncover the window of the Mercury Light Source. Spectral lines of 365 nm wavelength

will shine on the cathode in the phototube.

1. Start previewing in Capstone and click the first row in the table display
2. Adjust the VOLTAGE ADJUST knob on the DC Power Supply until the digital meter on the DC Current Amplifier shows that the current is zero.
3. Press “Keep Sample” on the Sample Control bar to record the magnitude of the stopping potential for the 365 nm wavelength in the table display.
4. Rotate the filter wheel until the 405 nm filter is aligned with the white line. Spectral lines of 405 nm wavelength will shine on the cathode in the phototube.
5. Adjust the VOLTAGE ADJUST knob on the DC Power Supply until the digital meter on the DC Current Amplifier shows that the current.
6. Click the second row of the table display and press “Keep Sample” to record the magnitude of the stopping potential for the 405 nm wavelength in table display.
7. Repeat the measurement procedure for the other three filters. Record the magnitude of the stopping potential for each wavelength in the table, and then press “Stop” in the software.
8. Repeat all the measurements for the 2 mm and 8 mm apertures.
9. Turn off the MERCURY LAMP power switch and the POWER switch on the other pieces of equipment. Rotate the filter wheel until the 0 nm filter is aligned with the white line. Cover the windows of the Mercury Light Source Enclosure and Photodiode Enclosure.