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Homework 13 Question 4

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The question reads: 

Two light sources are used in a photoelectric experiment to determine the work function for a particular metal surface. When green light from a mercury lamp (λ = 546.1 nm) is used, a stopping potential of 0.710 V reduces the photocurrent to zero.

I understood part A but can't seem to figure out part B:

(b) What stopping potential would be observed when using light from a red lamp (λ = 690.0 nm)? 

I've tried using the equation Kmax = e*V and solving for V. When first solving for Kmax, using Kmax = E - W, I found E by diving 1240/690nm to get 1.797 and have been using 0.734 as my W as that is the max kinetic energy of electrons. Once I have Kmax, I've tried a lot of different operation with 0.710 V and can't seem to get the right answer. Where am I going wrong?

asked Dec 2, 2014 in Intro College Physics by anonymous

1 Answer

0 votes
Based on your calculation in part (a), the work function should be 1.56 ev.  ||eV_s=hf-W||.

Using this work function, you can find the new stopping voltage with a different wavelength. ||eV_s=hf-W=1.797-1.56||.
answered Dec 2, 2014 by PhysicsDude (21,750 points)
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