# The Photoelectric Effect.

1. Sep 17, 2007

### Marghk

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

Having some problem with this question:

The threshold fequency for a material is 5.0*10^14 Hz. Find (a) the work function and (b) the maximum velocity of electrons ejected by radiation of frequency 8.0*10^14 Hz. The mass of an electron is 9.1*10^-31kg.

2. Relevant equations

(a) Can easily be found with W = hf.
: 6.62*10^-34*5*10^14
= 33.1*10^-20J

My teacher then asked me to calculate the above answer into Electron Volts, which i'm unsure of the answer.

(b) is also giving me some problems. I'm using the equation KE = hf - W, but I don't know where to finish the equation. Below is my attempt.

3. The attempt at a solution

KE(max) = hf - W
= (6.62*10^-34*8*10^14) - (33.1*10^-20)
= 19.86*10^-20J

After this, I get stuck :S I know I need to incorporate the mass of the electron in, but I can't figure it out. If anyone could explain this, it would be great :D

2. Sep 17, 2007

### Mindscrape

So the Joules to eV is pretty simple, so I'm going to omit it, though still feel free to ask for help. 1 electron volt = 1.60217646 × 10-19 joules

The mass of the electron is conveniently placed in units of eV/(m/s)^2, specifically for working in eV. The electron mass, in this form, is given by 0.511 MeV/c^2. Does this help?