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How does Einstein's photoelectric equation describe an ejected electron's energy?

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The photoelectric effect: Light interacting with matter — photoelectric effect Explanation of the photoelectric effect.

Albert Einstein's photoelectric equation describes the maximum kinetic energy of an electron ejected from a material surface when it absorbs a photon. The equation is expressed as:

$E_{k} = h ν - ϕ$

In this formula:

$E_{k}$ : The maximum kinetic energy of the ejected photoelectron.12
$h$ : Planck’s constant.13
$ν$ : The frequency of the incident radiation.14
$ϕ$ (or $ψ$ ): The work function, which represents the minimum energy required for an electron to escape the surface of the metal.124

Einstein’s model posits that light is absorbed in discrete quanta. When a photon strikes an electron, it transfers its energy ( $h ν$ ) to the particle. If this energy exceeds the work function of the material, the electron is ejected, and any remaining energy manifests as the electron's kinetic energy. This relationship demonstrates that the energy of the emitted electron depends on the frequency of the light rather than its intensity.243