# Homework Help: Modern Physics Photoelectrons

1. Nov 10, 2008

### xlzhsteven

Light of 300 nm wavelength strikes a metal plate, and photoelectrons are produced moving as fast of 0.002c. What is the work function of the metal?

2. Nov 10, 2008

### hage567

What have you tried so far? Please show what work you've done. We don't give out solutions here.

3. Nov 10, 2008

### xlzhsteven

I don't know what equations to use. Do I have to use the moving speed to find the energy, but I don't know how to use that 300nm since it's not the cutoff wavelength.

4. Nov 10, 2008

### borgwal

The electrons have an "excess" energy: so the work function should equal the difference between the photon energy and the excess energy.

5. Nov 10, 2008

### xlzhsteven

Should I use 0.5mv^2=hc/wavelength-work function, then what should I use for the mass in 0.5mv^2, the mass of an electron?

6. Nov 10, 2008

### hage567

Yes, you use the mass of an electron.

7. Nov 10, 2008

### xlzhsteven

So I have 3.108 for the answer of the work function

8. Nov 10, 2008

### xlzhsteven

is that right?

9. Nov 10, 2008

### hage567

Seems reasonable to me.

10. Nov 10, 2008

### borgwal

11. Nov 10, 2008

### xlzhsteven

3.108eV

12. Nov 10, 2008

### borgwal

okay, that sounds like the right order of magnitude.