- #1
fluidistic
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Homework Statement
A monochromatic light beam with wavelength [tex]\lambda =405 nm[/tex] and intensity [tex]3 \times 10 ^{-9}\frac{W}{m^2}[/tex] points to one of the plates of a plane metallic capacitor (photocathode). We apply a difference of potential of 1.15V between the 2 plates in such a way that we slow down the photoelectrons. A pico-ammeter shows a null current.
1)What's the maximum kinetic energy of the electrons?
2)What's the work function of the metal?
3)How many photoelectrons are emited by unit of area over unit of time?
4)What's the maximum wavelength of the radiation that can detach electrons from the metal?
2. The attempt at a solution
Not sure, but I believe that the maximum kinetic energy is [tex]E_K=hf-\phi[/tex] where [tex]\phi[/tex] is the work function and is worth [tex]hf_0[/tex]. That is, according to http://en.wikipedia.org/wiki/Photoelectric_effect.
What confuses me is the difference of potential of 1.15V.
Anyway, if the pico-ammeter shows [tex]0 \times 10 ^{-12}A[/tex], it means that the smallest current it can measure is [tex]1 \times 10 ^{-12}A[/tex]. I'm sure I need this data in order to solve part 1). I also think I'd solve part 2) before part 1)...
I really don't know how to solve the problem.