Overview of The Experiment of Photoelectric Effect and Determination of a Value for h, Planck's Constant

When light is incident on certain metallic surfaces, electrons are emitted from the surface–This is called the photoelectric effect–The emitted electrons are called photoelectrons. The successful explanation which enabled the first convincing experimental verification of quantum theory  had been provided by Einstein. In this article, light of a known frequency is assumed to shine upon the alkali metallic surface (potassium) acting as the photocathode in an evacuated tube. The photocathode is irradiated by light of approximately only one wavelength or colour (quasi-monochromatic light), and a voltage is applied between the anode (where the current is measured) and cathode so that it opposes the energy of the emitted photoelectrons. The potential energy gained (or kinetic energy lost) is eV where e is the charge of the electron and V is the potential difference or voltage between the anode and cathode. The voltage required to “just” stop the current flow V_s will thus be proportional to the maximum kinetic energy of the emitted. Indeed, the purpose of this article is to overview Einstein’s theory of the photoelectric effect, and determine a value for h, Planck’s constant by overview of the essential part of the experiment that served to establish the quantum theory of radiation.