weirdguy99
Member
Hey, there is an answer to the following question that I dont understand.
Question: During an experiment, a beam of ultraviolet light, of wavelength 200nm, is incident on a target metal sheet. The UV light release photoelectrons from the metal. The maximum kinetic energy of the photoelectrons was measured.
If a second beam of ultraviolet light, of equal intensity to the original ultraviolet beam, but of a shorter wavelength, was used in the experiment, compare the photoelectrons released by the original beam with those produced when the second ultraviolet light is used.
Answer: Frequency of the light has increased so the energy of each photon is larger. The new beam will liberate photoelectrons with a greater maximum kinetic energy (I GET THIS) but, because the intensity of the beam is equal to that of the original, the total energy per unit area is unchanged (WTF?) and, because each photon has a higher individual energy, there will be less photoelectrons being liberated from the surface than was the case with the original UV source.
Now, I understand that and increase in the frequence = increase in energy which means the photoelectrons will have a greater kinetic energy (move faster).
But why is there a change in the amount of photoelectrons being liberated? What is this total energy per unit area is unchanged thing??
The same amount of photons are hitting the metal but the only change is the energy in each photon which is larger than the first UV Ray. Shouldn't this mean that the amount of photoelectrons being liberated is the same as before, just the speed at which they travel is increased?
Thanks.
Question: During an experiment, a beam of ultraviolet light, of wavelength 200nm, is incident on a target metal sheet. The UV light release photoelectrons from the metal. The maximum kinetic energy of the photoelectrons was measured.
If a second beam of ultraviolet light, of equal intensity to the original ultraviolet beam, but of a shorter wavelength, was used in the experiment, compare the photoelectrons released by the original beam with those produced when the second ultraviolet light is used.
Answer: Frequency of the light has increased so the energy of each photon is larger. The new beam will liberate photoelectrons with a greater maximum kinetic energy (I GET THIS) but, because the intensity of the beam is equal to that of the original, the total energy per unit area is unchanged (WTF?) and, because each photon has a higher individual energy, there will be less photoelectrons being liberated from the surface than was the case with the original UV source.
Now, I understand that and increase in the frequence = increase in energy which means the photoelectrons will have a greater kinetic energy (move faster).
But why is there a change in the amount of photoelectrons being liberated? What is this total energy per unit area is unchanged thing??
The same amount of photons are hitting the metal but the only change is the energy in each photon which is larger than the first UV Ray. Shouldn't this mean that the amount of photoelectrons being liberated is the same as before, just the speed at which they travel is increased?
Thanks.
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