Formulas & tables/Physics/Atomic and nuclear physics/Einstein's equation (photoelectric effect)

Einstein's equation (photoelectric effect)

hf=W+Ekhf=W+E_k

Result unit: J (often eV)

What it describes

The photon's energy is used for the electron's work function and for its kinetic energy.

Symbols

hh
Planck's constant
[J·s]
ff
frequency of light
[Hz]
WW
work function
[J]
EkE_k
kinetic energy of the electron
[J]

Where it comes from

A photon ejects an electron from a metal only when its energy exceeds the work function. The surplus becomes the electron's kinetic energy. Below the threshold there is no effect, regardless of the light intensity.

When to use it

Photoelectric effect, photocells, photovoltaic panels.

Example

A photon of energy 5 eV strikes a metal with a work function of 2 eV. Calculate the electron's kinetic energy.
Substitutionhf=5hf=5 eV, W=2W=2 eV.
ResultEk=5−2=3E_k=5-2=3 eV.

Related formulas

Photon energy Mass–energy equivalence

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