Calculating Maximum Kinetic Energy of Ejected Electrons After Wavelength Doubles

AI Thread Summary
The discussion revolves around calculating the maximum kinetic energy of ejected electrons when the wavelength of incident photons is doubled. The initial photon energy is 12 eV, and a stopping potential of 8.0 V is applied. Participants express confusion about how to approach the problem without a given frequency, but it is clarified that the energy can be related to wavelength using the equation E = h(c/λ). The relevant equation for maximum kinetic energy is derived as Ekmax = (h×c/λ) - (e×Vs - E), allowing for the calculation using known values. Understanding the relationship between energy, wavelength, and stopping potential is key to solving the problem.
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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.
 
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Fair enough, did you look at the third link on Google? The Yahoo Answer one?
 


JameB said:
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?
 


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

Ekmax = (h×c/λ) - (e×Vs-E)

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

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