Photoelectric effect threshold

1. Oct 13, 2014

Nairabhi

When a cm thick surface is illuminated with light of wavelength lambda,the stopping potential is V. When the same surface is illuminated by light of wavelength 2lambda , the stopping potential is V/3.The threshold wavelength for the surface is ?

2. Relevant equations

3. The attempt at a solution

2. Oct 13, 2014

Matterwave

Did you try to do this problem yourself?

3. Oct 14, 2014

Nairabhi

Yes i tried but i am unable to solve it.

4. Oct 14, 2014

Staff: Mentor

Hi Nairabhi. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

What equations do you have that you'll use here?

Last edited by a moderator: May 7, 2017
5. Oct 14, 2014

Nairabhi

See according to Einstein equation KE(Max)= Energy of photons - work function of surface, but since work function is not given i have assumed it
to be 0. And energy of photons is equal to hc/lamda and this energy is equal to KE(Max) or the stopping potential so using these equations and i am trying to find a relation between them and find the threshold wavelength .However i don't understand what role does the thickness of surface plays which is 1cm ?

Last edited by a moderator: May 7, 2017
6. Oct 14, 2014

Staff: Mentor

You should assume work function is non-zero, and is fixed at some value.

That material thickness may simply mean "of suitable thickness" for our purposes.

Does the textbook give the correct answer?