Principle

A photocell is illuminated with monochromatic light of different wavelengths from a filament lamp with interference filters. The maximum energy of the ejected electrons in the photo-cell depends only on the frequency of the incident light, and is independent of its intensity. The stopping voltage Uo at different light frequencies is determined by the U/I caracteristics of the photocell and plotted over the corresponding light frequency f. Planck's quantum of action or Planck's constant (h) is determined from this graph .

Benefits

• Experience the essence of the Nobel Prize: Planck (1918)
• Planck's "quantum of action" the most important proof in quantum physics measured directly within few hours with the photocell
• Modular setup with the photocell and interference filters
• Easy determination of h
• No darkroom required

Tasks

To determine Planck's quantum of action from the photoelectric voltages measured at different wave lengths

Learning objectives

• External photoelectric effect
• Work function
• Absorption
• Photon energy
• Anode
• Cathode