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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.