# Photo electric effect problem

## Homework Statement

A magnesium surface has a work.func of 3.68eV. El.mag. waves with wavelenght of 215nm strike the surface and eject electrons. Find the max Ek of the ejected electrons in eV.

## Homework Equations

E=Ek-W <=> Ek=(hc/lambda) - W

## The Attempt at a Solution

I convert eV to J and nm to m but i get -3.68*10^10eV, but the answer is suppoused to be 2.10eV.
I even re did it but got the same answer, where em I going wrong?

Thanks

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TSny
Homework Helper
Gold Member
Hello.
In order to see where you are going wrong, we need to see your entire calculation.

Ek=(hc/lambda)-W

((6.63*10^-34)*(3*10^8))/(2.15*10^-7) - (5.888*10^-9)

(9.25*10^-19) - ( (5.888*10^-9) = -5.887*10^-9 J / (1.6*10^-19) = -3.68*10^10eV

TSny
Homework Helper
Gold Member
Ek=(hc/lambda)-W

((6.63*10^-34)*(3*10^8))/(2.15*10^-7) - (5.888*10^-9)

(9.25*10^-19) - ( (5.888*10^-9) = -5.887*10^-9 J / (1.6*10^-19) = -3.68*10^10eV
Check the power of 10 for the work function expressed in Joules.

ah ye, there we go. thanks :)