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 (115 V, 50/60 Hz), 8000699 [UE5010200-115], Fundamentals of Atomic Physics](/imagelibrary/UE5010200-115/UE5010200-115_01_Experiment-Planck-s-constant-115-V-5060-Hz.jpg)
![Experiment: Planck’s constant (115 V, 50/60 Hz), 8000699 [UE5010200-115], Fundamentals of Atomic Physics](/thumblibrary/UE5010200-115/UE5010200-115_01_1200_1200_Experiment-Planck-s-constant-115-V-5060-Hz.jpg)
