The Photoelectric Effect
The photoelectric effect occurs when light is shined at a sheet of metal. Remember that photons have energy. When the light is shined, the photons collide with the metal atoms. The metal atoms then absorb energy from the photons. Because metals tend to form cations (by losing electrons), if the electrons absorb enough energy, they are ejected from the substance.
Electrons that are ejected are called photoelectrons.
The light shined at the metal is called the incident light.
However, not all light will cause the photoelectric effect. Keep in mind that electrons are attracted to the nucleus. The incident light must have enough energy to overcome these forces of attraction.
Threshold Frequency: the minimum frequency of light needed to eject an electron from a substance. Different substances have different threshold frequencies.
In order to eject photoelectrons, the incident light must have a frequency that is greater than or equal to the threshold frequency.
If the light has a lower frequency, it is impossible to eject electrons. Even if you hit the metal with one trillion photons, no electrons will be emitted. This is because of binding energy.
Binding Energy: The energy required to remove an electron from an atom (also known as ionization energy).
Recall that the frequency of a photon is directly proportional to its energy. A photon’s frequency must be high enough, so that its energy is greater than the binding energy.
If the incident light has enough energy, meaning that its frequency is above the threshold frequency, then it only takes a singular photon to eject an electron. If it does not have enough energy, it is impossible to eject an electron, regardless of how many photons collide with the metal.
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