Lesson 10, Topic 2
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The Photoelectric Effect

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The photoelectric effect is a phenomenon in which electrons are ejected from a metal when light is shone on the metal surface.

Electrons emitted in the photoelectric effect are known as photoelectrons.


Inconsistencies with Wave Model

The classical (wave) model of light stipulated that the energy of light depended on its intensity. Therefore, it predicted that ANY frequency of light could induce the emission of photoelectrons given that it was of a substantial frequency.

This was proven to be incorrect through experimentation, which revealed that:

  1. No photoelectric effect is observed for a particular metal until the incident light is above a threshold frequency, no matter the intensity of the light.
  2. Above that threshold frequency, electrons are immediately released from the metal.
  3. The kinetic energy of the released electrons is depended upon the type of metal surface and the frequency of light incident on the surface.

These phenomena were unexplainable with the classical model of light.

Maximum Kinetic Energy vs. Frequency

  • The lines are parallel as their gradients are equal to h
  • The x-intercepts, or threshold frequencies, are different for each type of metal
  • The y-intercepts, or the work functions, are different for each type of metal