Photoelectric effect and maximum kinetic energy

1. Aug 18, 2010

Hey guys, assume that i performed and experiment to measure the maximum kinetic energy of electrons released due to the photoelectric effect due to light falling on a metal target (i.e. Sodium).

KE = hf - W (where W = work function, f = frequency and h = Planck constant)

since KE = 1/2 mv^2

i need to find the work function of this metal due to the photoelectric effect, do i assume the the velocity of the electron (or photon confused :S) is traveling at 3x10^8 (c) ??

p.s. i have all other known variables excluding W

thanks.

2. Aug 18, 2010

ZapperZ

Staff Emeritus
Er.. why do you even need to make any assumption about the velocity? You have KE, and presumably, you can determine the photon energy. What's left is simply plug and chug into the photoelectric effect equation to get the work function!

Or am I missing something here?

Zz.

3. Aug 18, 2010

Oh very sorry i was not given the kinetic energy, however i knew the mass of the particle.
can't remember whether it was a photon or electron. In terms of calculating the work function for this particular experiment, is it the absorbed photons we need to consider in determining the work function?

very sorry for this silly question

4. Aug 18, 2010

ZapperZ

Staff Emeritus
So what exactly is this "experiment"?

You said that the experiment is to measure the max. KE. In most experiment, this is measured "directly", i.e. independent of the values of the work function, etc. In a standard photoelectric effect experiment, the max. KE is related to the stopping potential. So you get the value of the max. KE directly. This gives you ALL you need to find the work function of the metal.

Zz.

5. Aug 18, 2010

so then just say the stopping potential was 1.6 volts, how would you go on calculating W.

6. Aug 18, 2010

ZapperZ

Staff Emeritus
This is a description of a typical Photoelectric effect experiment in an undergraduate physics lab. Read it.

http://mypages.iit.edu/~segre/phys223/08F/lab10_223.pdf

BTW, this better not be part of a school-type work, because you should know better by now where such a question should go into.

Zz.

7. Aug 18, 2010