The photoelectric effect refers to the phenomenon when electrons from the surface of a metal are released in the presence of light (ultraviolet in most cases).
The following is a flow-on paragraph of all the important concepts:
The threshold frequency is the minimum frequency a photon must have in order for the photoelectric effect to occur.
This frequency is related to energy by E=hf. So a higher frequency photon will provide a higher energy to the electrons on the surface of the metal. Higher frequencies mean short wavelengths. UV has a wavelength range of 10 - 400nm, which is why the photoelectric effect will occur with UV light.
Closely related to the threshold frequency is the work function.
The work function is the minimum amount of energy required for the photoelectric effect to occur. The energy of the photon is used up overcoming the work function. Any remaining energy is given to the KE of the ejected electron. This "left over" energy determines the KE of the electron.
The KE of the electron is thus determined by 1.) the work function of the metal and 2.) the frequency (and hence energy) of the photon. More reactive metals have lower work functions, so less energy is required to dislodge an electron.
When the electrons move off the metal, a potential difference can be applied in the opposite direction. There will be a voltage when the electrons do not move, which means there is no current. This is the stopping voltage.
The stopping voltage will change according to the KE of the electrons, which in turn depend on the 2 points above...work function of metal and frequency of photon.
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