Photoelectric Effect Post-Module Assessment (28B)  [ENDORSED]

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Isabella Zizolfi 2F
Posts: 21
Joined: Fri Sep 29, 2017 7:05 am

Photoelectric Effect Post-Module Assessment (28B)

Postby Isabella Zizolfi 2F » Tue Oct 10, 2017 11:19 am

28. 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.
How much energy is required to remove an electron from one sodium atom?
What is the frequency of the incident light on the sodium metal surface?

Could you help me solving these two problems, please?

Michaela Capps 1l
Posts: 50
Joined: Thu Jul 27, 2017 3:00 am

Re: Photoelectric Effect Post-Module Assessment (28B)  [ENDORSED]

Postby Michaela Capps 1l » Tue Oct 10, 2017 12:43 pm

The work function is given to us in kJ/mol but we want it per electron so we use Avogadro's constant. First I converted kJ to J by multiplying my 10^3 because that's what's easiest for me in terms of conversions. (150*10^3 J/mol) x (1 mol/6.02*10^23)...moles cancel out so we are left with 2.50*10^-19J
For the next part, we find the energy of the photon and then use a form of E=freq/h. So E(photon)=threshold energy+E(k). E=(1.99*10^-19J)+(2.50*10^-19J)=4.49*10^-19 J. then we use frequency=E/h to solve. frequency= (4.49*10^-19 J)/(6.626*10^-34 Js). Jules cancel out and the answer left is 6.78*10^14/sec or Hz.

Hopefully that all made sense not being able to type normal fractions or greek letters!

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