# Threshold wavelength photoelectrons

1. Aug 14, 2006

### delongk

With what speed will the fastest photoelectrons be emitted from a surface wih threshold wavelength of 600nm when the surface is illuminated with light of wavelength of 400nm?

2. Aug 14, 2006

### ZapperZ

Staff Emeritus
Do you know the significance of the information given by the "threshold wavelength"? If I used a 600 nm light, what would be the energy of the photoelectrons that are emitted?

Zz.

3. Aug 14, 2006

### delongk

the energy would be equal to the work function at 600nm because when the wavelength is at the threshold the energy is always equal to the work function.

4. Aug 14, 2006

### delongk

how does that help? i still don't understand.

5. Aug 14, 2006

### d_leet

It tells you what the work function is.

6. Aug 14, 2006

### Astronuc

Staff Emeritus
Supplementing comments of ZapperZ and d_leet -

One must determine the energy of the 600 nm photon, and that is sufficient to liberate (remove) an electron (photoelectron), hence the threshold.

Calculate the energy of the 400 nm photon and compare to the energy of the 600 nm photon.

Remember, the shorter the wavelength, the higher the frequency, which means more energy.

7. Aug 16, 2006

### jasc15

E=hf. this is all you need