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In the photoelectric effect, metals eject electrons called photoelectrons when light shines on them. The alkali metals Li, Na, K, Rb, and Cs are particularly subject to the effect. Not just any frequency of light will cause the photoelectric effect. Red light, for example, will not cause the ejection of photoelectrons from potassium, no matter how intense the light. Yet even a very weak yellow light (v = 5.1 x 1014 s-1) shining on potassium begins the effect.
The red frequency has a lower number of photons per second which explains why it can’t push a photoelectron out of the alkali metal. The photons travel in sequence one after the other just like cars on a highway or bicyclists in a race. This explains why increasing the frequency causes the electrons to travel faster out of the alkali metal.
The weakest frequency provides the starting point in determination of an approximate mass of a photon. If 5.1 x 1014 photons per sec are shot at an alkali metal and it begins to release electrons, then it will be assumed to release one electron per 5.1 x 1014 photons per sec. Increasing the threshold frequency produces an increase in the number of electrons ejected, because the increasing the threshold frequency represents an increase in the light intensity. The starting point is important, since it provides a reference point. Increasing the frequency causes the electron to move faster which reinforces Newton’s third law.
If it takes 5.1 x 1014 photons to emit one photoelectron, then an electron can be divided up into 5.1 x1014 photons.
1 electron = 5.1 x 1014 photons
If the electron has a mass of 9.11 x 10-28 and 5.1 x 1014 photons can produce on electron, then the mass of a photon can be calculated to be 1.7867745 x 10-42 g.
Mass photon = Mass of electron / 5.1 x 1014 photons
Mass photon = 1.7867745 x 10-42 g |
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