# Photons of energy 12 eV are incident on a metal. It is found that current flows from

1. Apr 20, 2012

### stacker

1. The problem statement, all variables and given/known data

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?

2. Relevant 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.

3. The attempt at a solution

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

2. Apr 20, 2012

### JameB

3. Apr 20, 2012

### stacker

4. Apr 20, 2012

### JameB

Re: Photons of energy 12 eV are incident on a metal. It is found that current flows f

5. Apr 20, 2012

### stacker

Re: Photons of energy 12 eV are incident on a metal. It is found that current flows f

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?

6. Apr 20, 2012

### JameB

Re: Photons of energy 12 eV are incident on a metal. It is found that current flows f

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.