## Practice Midterm 8b

$c=\lambda v$

Dominique S 4E
Posts: 11
Joined: Fri Sep 28, 2018 12:27 am

### Practice Midterm 8b

A newly designed laser pointed with a certain frequency is pointed at a sodium metal surface. An electron is ejected from the metal surface with wavelength 1.10nm. What is the frequency of the light from the laser pointer? The work function of sodium is 150.6kJmol-1.

I'm not too sure which equations to use to set this problem up. Thanks!

Louis Zhao 4C
Posts: 30
Joined: Sun Oct 07, 2018 12:17 am

### Re: Practice Midterm 8b

In the midterm review today, Lyndon used the work function equation : E(photon) - Threshold energy = E(kinetic energy)
E(photon) = Plank constant(h)*frequency(v), threshold energy/work function is given, and E(kinetic energy) = 1/2(MV^2) where M is the mass of the electron and V is the velocity of the electron
So therefore the equation in variables is hv - threshold energy = 1/2(MV^2) and we solve for v(frequency)

SydBenedict2H
Posts: 60
Joined: Wed Nov 08, 2017 3:00 am

### Re: Practice Midterm 8b

On the same question, based on the reply, what is the V we use to solve for v? Its the velocity of the electron right? I feel like im just missing something super obvious here...

Anand Narayan 1G
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

### Re: Practice Midterm 8b

Make sure to use wavelength = h/p in order to find the velocity of the electron. Once you find the velocity, you then plug the values into KE = E - work function in order to solve for E. Once you find E, you use E = hV, in order to solve for frequency.