Calculating Maximum Kinetic Energy of Ejected Electrons After Wavelength Doubles

[stacker]

Homework Statement

Photons of energy 12 eV are incident on a metal. It is found that current flows from the metal until a stopping potential of 8.0 V is applied.
If the wavelength of the incident photons is doubled, what is the maximum kinetic energy of the ejected electrons?

Homework Equations

I am absolutely clueless. I feel like I'm supposed to use KE = hf - W but how am I supposed to know the frequency if it isn't given? So I don't think I'm supposed to use this one.
Please just lead me towards the right direction. I don't have a clue as to which equation to use.

The Attempt at a Solution

This question is gibberish to me and I don't know how to even approach it. Please help.

 

[JameB]

http://lmgtfy.com/?q=Photons+of+ene...imum+kinetic+energy+of+the+ejected+electrons?

 

[stacker]

http://lmgtfy.com/?q=Photons+of+ene...imum+kinetic+energy+of+the+ejected+electrons?

You actually think I went through all this trouble of logging onto this forum, copying down the question, and explaining why I don't know how to solve it before googling the equation...

 

[JameB]

Fair enough, did you look at the third link on Google? The Yahoo Answer one?

 

[stacker]

Fair enough, did you look at the third link on Google? The Yahoo Answer one?

Yes but it doesn't say how you get wavelength. Although E = hf and f = c/wavelength.
E = h(c/wavelength). In which case what is E?

 

[JameB]

It does. What that person did was used the relevant equations and formulated an equation that related the wavelength to the maximum energy.

E_kmax = (h×c/λ) - (e×V_s-E)

Now plug in the data you know, and use two variables for the wavelength and solve for the ratio.