Photoelectric Effect Online Assessment Q34

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Varsha Sivaganesh 1A
Posts: 51
Joined: Thu Jul 13, 2017 3:00 am

Photoelectric Effect Online Assessment Q34

Postby Varsha Sivaganesh 1A » Wed Oct 11, 2017 8:46 pm

The question is:
B. If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the emitted electrons?

So from part A, I got 7.22 x 10^-19 J as the threshold energy. For this question, I tried using the equation E = hv and then substituting v = c/wavelength and when I did all that I got 1.02 x 10^-18 J, which I thought was the energy of the photon. So then I subtracted both those numbers, and ended up getting an answer that didn't fit any of the choices (and sadly, the answer is not none of the above lol). What am I doing wrong?

Nehal Banik
Posts: 64
Joined: Thu Jul 13, 2017 3:00 am

Re: Photoelectric Effect Online Assessment Q34

Postby Nehal Banik » Wed Oct 11, 2017 8:59 pm

This problem is discussing the photoelectric effect meaning that the energy per photon of energy reaches the minimum energy requirement to free and electron from the piece of metal. Once it reaches this minimum energy requirement or the threshold energy level, if the energy per photon exceeds the threshold energy then there will be excess energy which is called the kinetic energy of the electron that is freed. This kinetic energy is equal to the Ephoton- threshold energy= Eexcess (Kinetic energy)


Alright so when you find out the threshold energy in Joules, you need to find the Energy per Photon where you use the equation E/photon= (h)(c)/(wavelength) once you find this answer in joules it should be (6.626x10^-34) x (3.0x10^8) / (1.09x10^15m) which should equal 1.0246x10^-18, so now you take the threshold energy and the energy per photon and subtract them.
Ephoton- threshold energy= Eexcess (Kinetic energy) = (1.0246x10^-18) - ((7.22x10^-19) which should equal roughly 3.026 x 10 ^-19 kg x m^2, which should be one of the answer choices.

Hope this helps, if you have any questions please post a reply, I can help elaborate more.


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