Photo electric effect problem.

[btbam91]

In a photoelectric-effect experiment, the stopping potential at a wavelength of 400 nm
is 25.7% of the stopping potential at a wavelength of 300 nm. Of what metal is the
cathode made?

So I need to find the stopping potential of the metal with a wave length of 400 nm, but first I need to find the stopping potential of the metal with a wave length of 300 nm.


Using:

V(stop)=Kmax/e

Kmax=hf-Eo(work function)

How do I find the work function for the 300 nm?


Thanks.

 

[gneill]

I believe that the problem states that it is the same metal for both cases. That is, the same cathode has 400 nm light, then 300 nm light shone on it, and the result was that the stopping potential was less for the longer wavelength light (which is expected), and in fact was only 25.7% of the stopping potential for the shorter wavelength light.

Sounds like a case of setting up two equations in two unknowns and solving. Write expressions for both stopping potentials, then use the given information about their numerical relationship.