## Example 1.5 c

Isabel Jabara 1C
Posts: 34
Joined: Fri Apr 06, 2018 11:03 am

### Example 1.5 c

In example 1.5 in the textbook part c, we are told to set Ek to 0 to find the longest wavelength or radiation that is able to eject an electron, so hv=phi. They then concluded that lambda=ch/phi. How did they get to this conclusion?

Eduardo R 1L
Posts: 8
Joined: Mon Apr 09, 2018 1:38 pm

### Re: Example 1.5 c

So we know the equation relating wavelength and frequency (lambda,v) to speed of light c. lambda*v=c this can also be rearranged to
v=c/lambda dividing each side by lambda.
Because h*v=phi, we can substitute v with c/lambda giving us ... (h)(c/lambda)=phi, then you can multiply each side by lambda obtaining
h*c=lambda*phi, then divide each side by phi to isolate lambda!

Chem_Mod
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### Re: Example 1.5 c

Please post full details of the question for everyone else.

Eduardo R 1L
Posts: 8
Joined: Mon Apr 09, 2018 1:38 pm

### Re: Example 1.5 c

Isabel Jabara 1C wrote:In example 1.5 in the textbook part c, we are told to set Ek to 0 to find the longest wavelength or radiation that is able to eject an electron, so hv=phi. They then concluded that lambda=ch/phi. How did they get to this conclusion?

Here is the question for everyone else! :)
What is the longest wavelength of electromagnetic radiation that could eject electrons from potassium? The work function of potassium is 2.29 eV.