1B.15a DeBroglie or KE equation

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Charlene D 3H
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Joined: Wed Sep 30, 2020 9:54 pm

1B.15a DeBroglie or KE equation

Postby Charlene D 3H » Fri Oct 16, 2020 6:10 pm

The velocity of an electron emitted from a metallic surface by a photon is 3.6x10^3 km/s.
What is the wavelength of the ejected electron?

For this problem I used KE=(1/2)(mv^2) after converting km/s to m/s and using the mass of an electron. I then used lambda=(hc)/KE to find wavelength. However I didn't get the correct answer. The textbook key says to use the DeBroglie relationship to solve for wavelength but I am wondering if the KE equation should have worked for this problem as well.
If you used the KE equation can you state the values and steps you used so I can see where I made a calculation error?
Thank you so much.

IsaacLaw1E
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Re: 1B.15a DeBroglie or KE equation

Postby IsaacLaw1E » Fri Oct 16, 2020 6:50 pm

E = hv is for photons and electromagentic radiation, not electrons, so I don't think you can't really use that equation with the kinetic energy of an electron. DeBroglie's equation was developed to adapt wave properties to particles, so you would use that equation for wavelengths of electrons.

Charlene D 3H
Posts: 95
Joined: Wed Sep 30, 2020 9:54 pm

Re: 1B.15a DeBroglie or KE equation

Postby Charlene D 3H » Sun Oct 18, 2020 12:55 pm

Okay that makes sense thank you!

rhettfarmer-3H
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Re: 1B.15a DeBroglie or KE equation

Postby rhettfarmer-3H » Sun Oct 18, 2020 4:46 pm

i actually had the same question in my discussion this week. And yeah you don't use it for the sake of it being a good representation of wave.

I showed the work to incase you need directionality. you just need to find the electron mass which is a constant and rearrange the equation of lamada= h/p ;)
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