## Online Modules #28A

$c=\lambda v$

Ashley R 1A
Posts: 41
Joined: Sat Aug 24, 2019 12:16 am

### Online Modules #28A

I was going over the online modules for the "Photoelectric Effect" section on the 14A website and came across this problem in the post-module assessment:

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61x10^5m/s. The work function for sodium is 150.6 kJ/mol.
What is the kinetic energy of the ejected electron?

I'm getting stuck on how to solve this. When given the velocity I assumed you would use E = 1/2mv^2 to solve for energy but I"m not sure where you're supposed to get the mass of the electron? If someone could walk me through this problem that'd be great! :)
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AlyshaP_2B
Posts: 112
Joined: Wed Sep 18, 2019 12:19 am

### Re: Online Modules #28A

I was confused about the same thing when I came across this question! I think the mass of an electron is a constant, it's about 9.11 × 10^(-31) kilograms.
Last edited by AlyshaP_2B on Thu Oct 10, 2019 5:03 pm, edited 2 times in total.

Zaynab Hashm 2I
Posts: 110
Joined: Wed Sep 11, 2019 12:15 am
Been upvoted: 1 time

### Re: Online Modules #28A

You use the formula E (kinetic energy) = 1/2mv^2. The velocity is already given, but the mass you should use is the mass of an electron (a constant) which is 9.11 × 10^-31 kilograms.