## Photo electric effect

Anaranjo
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Joined: Wed Nov 18, 2015 3:00 am

### Photo electric effect

How does assuming that light energy consists of quanta help to explain the plot of kinetic energy against frequency in the study of the photoelectric effect?

Chem_Mod
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### Re: Photo electric effect

We can think of a case where one photoejects only a single electron from the metal surface. Since the photoejection of an electron depends on the frequency, rather than the intensity, it implies that an electromagnetic radiation of a particular frequency must have provided sufficient energy to knock out 1 electron. This in fact is the smallest energy a light source can provide to knock out a single electron, so we can assume light has "quanta" of energy which depends on the frequency or E=hv.

Manpreet Singh 1N
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### Photo electric effect

I am stuck on this question from the post assessment.
Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1.
A. What is the kinetic energy of the ejected electron?

I think I would use the Ek = 1/2 mv^2 equation, but what would I use at the mass of the electron? Is that information provided?

Julia Nakamura 2D
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Joined: Wed Sep 21, 2016 2:57 pm

### Re: Photo electric effect

Yes, the mass of the electron will be given to you (with the correct number of sig figs that you should use). The mass that I used for that problem was 9.11 x 10^-31. So, multiplying the mass of the electron times the velocity (6.61 x 10^5)^2 and dividing by two should give you 1.99 x 10^-19 J as the kinetic energy of the ejected electron.