The photoelectric effect is the phenomenon where electrons are emitted from the surface of a material, typically a metal, when it is exposed to electromagnetic radiation such as ultraviolet light. These emitted electrons are called photoelectrons

. Key points about the photoelectric effect:

• Electrons are ejected only if the incident light has a frequency above a certain threshold frequency specific to the material. Light below this frequency, regardless of its intensity, will not cause electron emission

• The kinetic energy of the emitted photoelectrons depends on the frequency of the incident light, not its intensity. Increasing the light intensity increases the number of emitted electrons but does not increase their kinetic energy

• The minimum energy required to release an electron from the material's surface is called the work function (denoted WWW or Φ\Phi Φ) of the material

• Albert Einstein explained the photoelectric effect by proposing that light consists of discrete packets of energy called photons. Each photon has energy proportional to its frequency ν\nu ν, given by E=hνE=h\nu E=hν, where hhh is Planck's constant

• The maximum kinetic energy Kmax⁡K_{\max}Kmax​ of the emitted electrons is given by Einstein’s photoelectric equation:

Kmax⁡=hν−WK_{\max}=h\nu -WKmax​=hν−W

This means electrons are emitted only if ν\nu ν (the frequency of light) is greater than the threshold frequency ν0\nu_0 ν0​ (where W=hν0W=h\nu_0 W=hν0​)

The photoelectric effect provided crucial evidence for the quantum nature of light and helped establish the foundation of quantum mechanics

. In summary, the photoelectric effect is the emission of electrons from a material's surface when illuminated by light of sufficiently high frequency, explained by the particle nature of light photons transferring energy to electrons