# What was Einstein's explanation for the photoelectric effect?

Mar 5, 2016

It was observed experimentally that various metals ejected electrons when light of specific or higher frequency was shown on their surface. The wave theory of light could not explain this phenomenon.

#### Explanation:

In 1900 Max Planck made an ad hoc mathematical assumption of quantized energy to explain Black body radiation.

He proposed the famous expression $E = h \nu$.

$E$ being energy, $\nu$, the frequency of radiated energy and $h$ is Planck's Constant. Subsequently in 1905 Albert Einstein extended Planck's black body model to propose his solution to explain the photoelectric effect and all other associated observations.

He described light as composed of discrete quanta, now called as photons, as opposed to continuous waves. Einstein extended Planck's assumption to light and proposed that the energy in each quantum of light was equal to the frequency multiplied by a constant. A single photon, whose frequency was above the threshold frequency for a specific metal, has the required energy to eject one electron thus creating the observed photoelectric effect

To explain other experimental results of photoelectric effect, Einstein theorized the following equation:

$h \nu = \phi + K {E}_{\max}$

where $h$ is Planck's constant, $\nu$ frequency of incident light, $\phi$ work function of the metal and $K {E}_{\max}$ the maximum kinetic energy of the ejected electron(s). For photoelectric effect to occur, the energy of the photon must be greater than the work function. 