## Wavelength and KE

$E=hv$

605379296
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### Wavelength and KE

How do we find wavelength when we're given the kinetic energy in Joules?

Posts: 48
Joined: Sat Aug 17, 2019 12:16 am

### Re: Wavelength and KE

By using the DeBroglie and Kinetic Energy Equations, wavelength comes out equaling λ = h/√(2mE)

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Joined: Fri Aug 09, 2019 12:16 am

### Re: Wavelength and KE

If you add the kinetic energy to the threshold energy, you get the energy per photon that's being used in this photoelectric experiment. From there you use E=hv and c=v(wavelength) to find the wavelength.

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### Re: Wavelength and KE

From the Kinetic Energy equation, you can isolate velocity and then substitute it into De Broglie's equation. This will give you: λ = h/√(2mKE). To solve for the wavelength, you can then plug in the value that you’re given for kinetic energy along with Planck’s constant and the mass of an electron which is 9.11x10^-31 kg.

Kamille Kibria 2A
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### Re: Wavelength and KE

there are two ways to solve this. i would use the equation KE+threshold energy=energy of the photon. the threshold energy can also be called the work function of a certain metal, which has to be given to you. from there you get the energy of the photon, which is when you can use the equation Ephoton=hv where you will get the frequency, and then plug the frequency into the equation wavelength=c/v and you will get the wavelength.

the other way you could find the wavelength from the KE is by using the equation KE=(1/2)mv^2 and solving for v. (the m is mass of electron which is 9.11E-31kg which is given to you). after you get v you can plug that into De Broglie's equation which is wavelength = h/mv where h is planck's constant. hope that helps :)

RitaThomas_3G
Posts: 85
Joined: Wed Sep 30, 2020 9:40 pm

### Re: Wavelength and KE

Hey! So when I would be solving a problem like this, I would initially start out with what I am solving for, which is wavelength. So, I would start with this equation: $\lambda = \frac{h}{mv}$.
Then, after looking at the equation, I see what values I already have. I know that h is Planck's constant, and m can be solved for given whatever molecule/particle the question is referring to. The only issue now is v. However, since we know that we are given Kinetic Energy, we can use that equation to solve for v.
Then, you can just plug this equation into the first equation to get this final equation for wavelength: $\lambda = \frac{h}{\sqrt{2mKE}}$