Planck’s Constant Apparatus — The Photoelectric Effect
Give a Reasonable Order of Magnitude for Planck’s ConstantDemonstrate the photoelectric effect and the principle of applying a “backing p.d.” to reduce anode current to zero with this precision instrument. A newly designed photoelectric unit comes equipped with a photoemissive Caesium Antimony cathode with a special response of 185-650 nm. When light frequency strikes the cathode, electrons are released and would normally reach the anode producing a current which can be registered on a very sensitive instrument, such as an electrometer. The p.d. from an internal PP3 type cell can be adjusted to a value V where the anode current is just reduced to zero. This apparatus enables values of V to be found for various frequencies of light by placing each of the six color filters in turn over the cell. Includes the main unit with screened lead, six color filters, three narrow band filters, and a picoammeter.
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