How to calculate the work function of a metal?

[madayag1]

HI I am 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.

 

[ap123]

W=hc/Lambda -Ek
=(6.63E-34J.s)(3.00E8m/s)/3.50E2m)-1.20eV

Hello madayag1
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.

 

[darkxponent]

Did you convert the units, Joule to eV?

 

[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.

 

[madayag1]

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

 

[ap123]

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

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

 

[barryj]

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

 

[madayag1]

book doesn't say what units is requested

 

[barryj]

I think work function is normally in ev. Check your math however.