Finding frequency

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Gisela F Ramirez 2H
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Joined: Fri Sep 28, 2018 12:27 am

Finding frequency

Postby Gisela F Ramirez 2H » Sun Dec 09, 2018 2:35 am

An electron was ejected from a sodium metal surface with light of a given frequency. If the wavelength of the ejected electron is 1.1 nm, what was the frequency of the incident light? The work function of sodium is 150.6 kJ/mol.

I always get stuck on finding the velocity in the Kinetic energy portion of E=threshold+KE. How do you find velocity with what we are given in the question?

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Joined: Fri Sep 28, 2018 12:25 am

Re: Finding frequency

Postby RandallNeeDis3K » Sun Dec 09, 2018 2:54 am

Since we are given the wavelength of an electron, you must use the de Broglie equation, and in this case we would use it to find the velocity of the electron. (wavelength of particle = plancks constant / momentum (mass x velocity)). Since we know all values except for velocity, we can find it. Once we have velocity, we can find velocity in the equation: plancks constant x frequency (Energy) - work function (Energy required to eject) = 1/2 x mass x velocity^2 (Kinetic energy). We have all values except frequency, which the question is asking to solve for. Hope this helps!

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Joined: Tue May 01, 2018 3:00 am

Re: Finding frequency

Postby 904837647 » Sun Dec 09, 2018 3:20 am

E=hv!! So substitute planck's constant for h and set that equation= to work function + Ek

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