# Classical radius of an electron and its implications prob.

1. Feb 23, 2007

### Delzac

1. The problem statement, all variables and given/known data
The classical radius of an electron is 2.82 x 10-15 m. If a material is radiated with sunlight with an intensity of 500W/m2, calculate using classical arguments the time required for an electron to gain an energy of 1eV. How does this result compare with electron emission in the photo-electric effect?

2. Relevant equations
$$E= hf$$

3. The attempt at a solution

I completely do not have any idea how to do this question. Can anyone provide my with the necessary equation. So far i do not have any idea which equation has " t" in it.

And the difference between classical and modern physic is :
Electrons are emitted from the surface almost instantaneously (less than 10-9 secs) even at low intensities.
Classically the electrons would require some time to absorb the incident radiation before they acquire enough kinetic energy to escape from the metal.

Any help will be greatly appreciated.

2. Feb 23, 2007

### Saketh

Since we are given a power in the intensity, once you find the energy required in terms of the power, you can find the time.

3. Feb 24, 2007

### MarkusNaslund19

You can then get the power emitted onto the electron.

P=IA

Now P=Et, solve for t. Don't forget to use the same units here.

As for comparing, find some way to get wavelength, i guess, from the intensity you are given and use E=hf.

4. Feb 24, 2007

### Delzac

kk got it thanks.