The threshold frequency is the minimum frequency a photon can be and still just overcome the work function (Φ) of a particular material. The threshold frequency is directly proportional to the work function and is given by f=E/h, where E is equal to Φ, f is the threshold frequency and h is Planck's constant.Providing the frequency of the photon is greater than the threshold frequency, the electron absorbing the photon will escape the material. However, if the frequency of the photon is greater than this the electron will have excess energy after escaping the surface of the material, which is present as kinetic energy, given by E_{k} = E - Φ (E is given by E=hf).