Light can act as a wave or it can act as a particle. The photoelectric effect gives evidence of light acting as a particle. In the photoelectric effect, when light with a high enough energy strikes a metal, electrons are ejected from the metal. The binding energy for a metal is the energy keeping an electron in the metal. This energy must be overcome to eject an electron. When an experiment is run with the photoelectric effect, there's a particular frequency below which no electrons are ejected. This frequency is called the threshold frequency. Above the threshold frequency, electrons are ejected from the metal. If light only acts as a wave, we could increase the amount of energy by increasing the amplitude of the wave, which corresponds to increasing the intensity of the light. However, when the experiment is run with a higher intensity light, the threshold frequency doesn't change. The only thing to change is the rate at which electrons are ejected from the metal. This result only makes sense if light is acting not as a wave, but as a particle. We call a particle or packet of light energy a photon or quantum of light. The energy of a photon depends on the frequency according to the equation: Energy equals Planck's constant times Frequency. Since frequency and wavelength are inversely proportional, we can also say: Energy equals Planck's constant times Frequency divided by the Wavelength. So with our photoelectric effect, an electron is absorbing the energy of a photon. The energy of the photon is equal to h c over lambda or h nu. The energy keeping our electron in the metal is the binding energy. The energy of the photon must overcome this binding energy to eject the electron. Our binding energy is equal to Planck's constant times the threshold frequency, which is the frequency when we just begin to eject electrons. Looking at our photoelectric effect, our binding energy is keeping the electron in the metal. If the energy of our photon is greater than the binding energy, then we'll eject the electron. According to the Law of Conservation of Energy, we cannot create or destroy energy. If the energy of the photon is greater than the binding energy, the excess energy absorbed by the electron is converted into kinetic energy according to the equation: kinetic energy of the electron equals Planck's constant times the frequency of our photon subtract the binding energy of the electron. So with our photoelectric effect, the electron has absorbed a photon with an energy greater than the binding energy. The extra energy is converted into kinetic energy for the electron. To calculate the kinetic energy, we take the energy of the photon absorbed by the electron minus the binding energy of the electron, which was the energy keeping the electron in the metal.