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jimmypoopins

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## Homework Statement

In an advanced laboratory class a student performs the photoelectric experiment. Ultraviolet light is shone on a particular metal and the stopping potential is measured at the same time. It is found that 2.61 V is needed to stop all the electrons when the wavelength of the light is 285 nm, and 4.53 V for a wavelength of 207 nm. What is the work function of the metal?

## Homework Equations

[tex]hf=eV+\phi[/tex]

Find [tex]\phi[/tex]

## The Attempt at a Solution

(1)[tex]hf_{1}=eV_{1}+\phi[/tex]

(2)[tex]hf_{2}=eV_{2}+\phi[/tex]

divide 1 by 2 to get rid of h, and we get

[tex]\frac{f_{1}}{f_{2}}=\frac{eV_{1}+\phi}{eV_{2}+\phi}[/tex]

i can't seem to solve for [tex]\phi[/tex] and get the correct answer. I've tried doing it both algebraically(sp, sry) and with a calculator. possibly I'm putting the numbers in wrong? i have:

[tex]e=1.6022*10^-19 C[/tex]

[tex]f_{1}=285*10^-9 m[/tex]

[tex]f_{2}=207*10^-9 m[/tex]

[tex]V_{1}=2.61V[/tex]

[tex]V_{2}=4.53V[/tex]

where am i going wrong? please help

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