# Homework Help: Photoelectric effect and kinetic energy

1. Apr 3, 2009

### confuse

hi
i have a small question:

how come not all emitted electrons have the same kinetic energy despite the radiation of only a single wavelength (that does cause emission of electrons) ?

thanks

2. Apr 3, 2009

### turin

The energy structure of the electrons in the metal gives a maximum energy of -φ (the "work function") w.r.t the free state, but the electrons can occupy energy states below this threshhold, as well.

3. Apr 4, 2009

### confuse

i dont want to be a troublesome person, but does it mean that the maximum kinetic energy that is calculated by the formula refers to free electrons, while others can occupy different energy levels and therefore have smaller kinetic energy?

thanks again

4. Apr 4, 2009

### turin

What formula?

5. Apr 5, 2009

### confuse

Ephoton = Φ + KEmax

Ephoton = hf is energy of the photon.

Φ is the work function of the metal.

KEmax is the maximum kinetic energy of the ejected electrons .

6. Apr 5, 2009

### turin

OK, no. It means that the maximum kinetic energy refers to only those electrons that have a maximum energy "in the potential well of the metal". Actually, not even all of these electrons will obtain the maximum kinetic energy in your formula, because the potential well has some nontrivial structure. For your purposes, it is probably sufficient to realize that there is a minimum required EM radiation frequency to free an electron.

Last edited: Apr 5, 2009