The photoelectric effect occurs when matter emits electrons when it is exposed to electromagnetic radiation like photons of light. This effect is studied because it is the introduction to quantum mechanics and wave/particle duality.
When surfaces are exposed to a sufficient amount of energetic electromagnetic energy, light is absorbed and electrons are emitted. The frequency differs depending on the material. The frequency photoelectric effect is within the spectrum of visible light for alkali metals, a near ultraviolet light for various other metals and extremely high-frequency radiation for non metals. This effect occurs when a photon has energy of just a few electron volts.