Homework Help: How to calculate the work function of a metal?

1. Jul 14, 2013

HI im doing this equation : 14. When a certain metal is illuminated at 3.50x10^2nm the maximum kinetic energy of the ejected electrons is 1.20 eV. Calculate the work function of the metal.
I did this:
E=Ek+W
W=E+Ek
W=hc/Lambda -Ek
=(6.63E-34J.s)(3.00E8m/s)/3.50E2m)-1.20eV
=-1.2

That answer is wrong the correct one is 2.35 eV. what did i do wrong, PLS help me ty and show me what I should of done so i Dont repeat this mistake again.

2. Jul 14, 2013

ap123

Look again at the figure you've used for the wavelength - you forgot the nm.
Also, the first part of the calculation is in J, but you've subtracted a value in eV from it.

3. Jul 14, 2013

darkxponent

Did you convert the units, Joule to eV?

4. Jul 14, 2013

barryj

The result of 'W=hc/Lambda " is in joules is it not? You cannot subtract ev from joules wiothout a unit conversion.

Also, you have ente3red your wavelength incorrectly.

5. Jul 14, 2013

srry it should be W=( (6.63E-34J.s)(3.00E8m/s) / (3.50E2nm) ) - 1.9E-19J = -1.9E-19

6. Jul 14, 2013

ap123

You've written the nm part for the wavelength, but did you include it in the calculation?

7. Jul 14, 2013

barryj

Check your math. The answer is not negative. Also, what units are reque3sted?

8. Jul 14, 2013