Objective: Determine Planck’s constant using the decelerating voltage method
In a modified version of a classic set-up, light of known frequency passes through a ring-shaped anode to collide with a cathode, where it causes electrons to be released due to the photo-electric effect. The energy of the electrons can be determined by applying a decelerating voltage, which compensates for the flow of electrons towards the anode until no electrons are flowing. This demonstrates that the cut-off value of the decelerating voltage which corresponds to a current of zero is not dependent on the intensity of the light. The energy of the electrons is therefore similarly independent of intensity. By obtaining the cut-off voltages for light of varying frequency, it is possible to calculate Planck’s constant.
![Experiment: Planck’s constant (230 V, 50/60 Hz), 8000700 [UE5010200-230], Fundamentals of Atomic Physics](/imagelibrary/UE5010200-230/UE5010200-230_01_Experiment-Planck-s-constant-230-V-5060-Hz.jpg)
![Experiment: Planck’s constant (230 V, 50/60 Hz), 8000700 [UE5010200-230], Fundamentals of Atomic Physics](/thumblibrary/UE5010200-230/UE5010200-230_01_1200_1200_Experiment-Planck-s-constant-230-V-5060-Hz.jpg)
![Planck’s Constant Apparatus (230 V, 50/60 Hz), 1000537 [U10700-230], Fundamentals of Atomic Physics](/thumblibrary/U10700-230/U10700-230_01_140_140_Planck-s-Constant-Apparatus-230-V-5060-Hz.jpg)
![Set of 15 Safety Experiment Leads, 75 cm, 1002843 [U138021], Circuits](/thumblibrary/U138021/U138021_01_140_140_Set-of-15-Safety-Experiment-Leads-75-cm.jpg)
![Barrel Foot, 1 kg, 1002834 [U13265], Bases](/thumblibrary/U13265/U13265_01_140_140_Barrel-Foot-1-kg.jpg)
![High Voltage Power Supply 5 kV (230 V, 50/60 Hz), 1003310 [U33010-230], Power Supplies](/thumblibrary/U33010-230/U33010-230_01_140_140_High-Voltage-Power-Supply-5-kV-230-V-5060-Hz.jpg)
![Tube Holder S, 1014525 [U185002], Electron Tubes S](/thumblibrary/U185002/U185002_01_140_140_Tube-Holder-S.jpg)
![DC Power Supply 0-500 V (230 V, 50/60 Hz), 1003308 [U33000-230], Power Supplies](/thumblibrary/U33000-230/U33000-230_01_140_140_DC-Power-Supply-0-500-V-230-V-5060-Hz.jpg)
![Function Generator FG 100 (230 V, 50/60 Hz), 1009957 [U8533600-230], Function Generators](/thumblibrary/U8533600-230/U8533600-230_01_140_140_Function-Generator-FG-100-230-V-5060-Hz.jpg)
![PC Oscilloscope 2x25 MHz, 1020857 [U11830], Oscilloscopes](/thumblibrary/U11830/U11830_01_140_140_PC-Oscilloscope-2x25-MHz.jpg)
![Electron Diffraction Tube S, 1013889 [U185711], Electron Tubes S](/thumblibrary/U185711/U185711_01_140_140_Electron-Diffraction-Tube-S.jpg)
![HF Patch Cord, BNC/4 mm Plug, 1002748 [U11257], Experiment Leads and Cables](/thumblibrary/U11257/U11257_01_140_140_HF-Patch-Cord-BNC4-mm-Plug.jpg)
![Helmholtz Coils, 300 mm, 1000906 [U8481500], Induction](/thumblibrary/U8481500/U8481500_01_140_140_Helmholtz-Coils-300-mm.jpg)
![Experiment: Electron Diffraction (230 V, 50/60 Hz), 8000704 [UE5010500-230], Fundamentals of Atomic Physics](/thumblibrary/UE5010500-230/UE5010500-230_01_140_140_Experiment-Electron-Diffraction-230-V-5060-Hz.jpg)
![Pocket Measuring Tape, 2 m, 1002603 [U10073], Accessory - Measurement of Length](/thumblibrary/U10073/U10073_01_140_140_Pocket-Measuring-Tape-2-m.jpg)
![Interferometer, 1002651 [U10350], Interferometer](/thumblibrary/U10350/U10350_01_140_140_Interferometer.jpg)
![Thomson Tube S, 1000617 [U18555], Electron Tubes S](/thumblibrary/U18555/U18555_01_140_140_Thomson-Tube-S.jpg)
![Digital Spectrometer LD, 1018103 [U22028], Spectrophotometer](/thumblibrary/U22028/U22028_01_140_140_Digital-Spectrometer-LD.jpg)
![Spectrum Tube Power Supply (230V, 50/60 Hz), 1000684 [U418001-230], Spectrum Tubes and Spectrum Lamps](/thumblibrary/U418001-230/U418001-230_01_140_140_Spectrum-Tube-Power-Supply-230V-5060-Hz.jpg)
![Spectrum Tube Helium, 1003408 [U41816], Spectrum Tubes and Spectrum Lamps](/thumblibrary/U41816/U41816_01_140_140_Spectrum-Tube-Helium.jpg)
![Spectrum Tube Hydrogen, 1003409 [U41817], Spectrum Tubes and Spectrum Lamps](/thumblibrary/U41817/U41817_01_140_140_Spectrum-Tube-Hydrogen.jpg)