The mathematical representation of the **photoelectric effect** is:

Since the energy of a photon (E_{photon}) is also equal to (h∙v) where h is Planck’s constant (6.626x10^{-34} J∙s) and v is the frequency (in Hz or s^{-1}), and work function can be denoted as ϕ, the photoelectric equation can be written as:

Therefore, the equation for work function, ϕ is:

In order to comply with the requirement that energy be conserved, Einstein showed in the photoelectric effect that the energy of a photon (hν) absorbed by a metal is the sum of the work function (ϕ), which is the minimum energy needed to dislodge an electron from the metal’s surface, and the kinetic energy (E_{k}) of the electron: hν = ϕ + E _{k}. When light of wavelength 358.1 nm falls on the surface of potassium metal, the speed (u) of the dislodged electron is 6.40 x 10^{5} m/s. What is ϕ (in J) of potassium?