Photoelectric effect

The photoelectric effect occurs when light shines on a metal surface and causes that material to emit electrons. These ejected electrons are called photoelectrons, and their behavior proved that light possesses properties of both waves and particles.

According to classical wave theory, higher intensity should mean more energy, but in the photoelectric effect, intensity only affects the total number of ejected electrons. The energy of the individual electrons depends entirely on the frequency, or color, of the light because light delivers energy in discrete packets called photons.

Albert Einstein explained the photoelectric effect in 1905, proposing that light consists of discrete energy quanta, which we now call photons. This groundbreaking discovery earned him the Nobel Prize in Physics in 1921, as it was a foundational pillar of quantum mechanics.

The threshold frequency is the minimum frequency of incoming light required to eject an electron from a specific material's surface. If the light's frequency is below this specific limit, no electrons will be emitted, regardless of how bright or intense the light is.