The photoelectric effect is a phenomenon that occurs when light falls on a metal surface and electrons are emitted from it. This effect was first observed by Heinrich Hertz in 1887 and later explained by Albert Einstein in 1905. The photoelectric effect established that light behaves like particles.

Explanation:
• The photoelectric effect involves the emission of electrons from a metal surface when light falls on it.
• When a photon of light hits the metal surface, it transfers its energy to an electron in the metal atom.
• If the energy of the photon is greater than the work function of the metal, the electron is ejected from the metal surface.
• The ejected electron is called a photoelectron.
• According to classical physics, the energy of a wave is proportional to its amplitude, so increasing the intensity of the light should increase the energy of the ejected electrons.
• However, experiments showed that increasing the intensity of the light did not increase the energy of the ejected electrons, but only increased their number.
• Einstein explained this phenomenon by proposing that light consists of particles called photons.
• The energy of a photon is proportional to its frequency, not its amplitude, so increasing the frequency of the light increases the energy of the ejected electrons.
• This is why increasing the frequency of the light, by using light of a shorter wavelength, increases the energy of the photoelectrons.
• The energy of the photoelectrons is given by the equation E = hf - Φ, where E is the energy of the photoelectron, h is Planck's constant, f is the frequency of the light, and Φ is the work function of the metal.
• The photoelectric effect is used in photovoltaic cells, which convert light energy into electrical energy.