# Homework Help: Modern Physics question

1. Feb 7, 2010

### Wardlaw

Modern Physics question!!

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

When radiation of wavelength 350nm is incident on a surface, the maximum kinetic energy of the photoelectrons is 1.2ev. What is the stopping potential for a wavelength of 230nm?

2. Relevant equations
$$\phi$$=hc/$$\lambda$$-eV0( V0= V 'nought')
I am unsure as to what other equations can be used.

3. The attempt at a solution
My attempt was to calculate $$\phi$$ for the 350nm wavelength, and then do the same for the 230nm wavelength.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 7, 2010

### thebigstar25

Re: Modern Physics question!!

in this problem you can make use of two equations:
(1) : Kmax = hc/lamda - workfunction (Kmax is the max. kinetic energy , lamda is the wavelength)

(2) : Kmax = eVs (Vs is the stopping potential)

your start is good .. when you get the work function for the 350 nm wavelength , use that workfunction again with equation (1) along with the 230 nm wavelength to get Kmax and then use equation (2) to get the stopping potential ..

note : you just need to calculate the workfunction just once since that value is fixed for a certain material .. :)