## Finding frequency

Gisela F Ramirez 2H
Posts: 61
Joined: Fri Sep 28, 2018 12:27 am

### Finding frequency

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?

RandallNeeDis3K
Posts: 34
Joined: Fri Sep 28, 2018 12:25 am

### Re: Finding frequency

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!

904837647
Posts: 67
Joined: Tue May 01, 2018 3:00 am

### Re: Finding frequency

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