Photoelectric effect classical approach

[mathilin]

Homework Statement

Assume that a point source of light gives 3 watt = 3 J/s of light energy.

a) assume uniform radiation in all dirrections, find the light intensity in ev/m²*s
b)Assuming some reasonable size for an atom, **** the energy/time incident on the atom for this intensity.

Homework Equations

resonable atom size = 10^-10m
I = E/(area*t)

The Attempt at a Solution

a) I think I got this one correct, however I'm not sure. Here is what I did:
I=E/(area*time) = ((3J/s)*(6.24x10¹⁸ ev/J))/(4 m²*s)
= 4.68X10¹⁸ ev/m^2*s

b) I have no idea what to do with this. I was thinking maybe find the surface area of the atom and divide that by the intensity? which would lead to (10^-20)/4.68X10¹⁸ ev/m^2*s

 

[anathema]

but that doesn't seem right. Any help would be appreciated.For part b), you are on the right track. The energy per unit time incident on the atom can be calculated by dividing the total energy (3 J/s) by the surface area of the atom (assuming it is a sphere with radius 10^-10m). This will give you the energy per unit time per unit area incident on the atom, which is the same as the light intensity at that point.

So, the calculation would be:
E/t = (3 J/s) / (4π*(10^-10 m)^2)
= 2.39 x 10^9 J/m^2*s

This is the energy per unit time incident on the atom. This value can also be expressed in units of ev/m^2*s by dividing by the conversion factor of 6.24 x 10^18 J/ev:
E/t = (2.39 x 10^9 J/m^2*s) / (6.24 x 10^18 J/ev)
= 3.83 x 10^-10 ev/m^2*s

So, the energy per unit time incident on the atom for this intensity is 3.83 x 10^-10 ev/m^2*s. This means that for every square meter of the atom's surface, 3.83 x 10^-10 ev of energy is incident on it every second.

 

[nlightner]

, which would give me a really small number. But I'm not sure if this is the correct approach or if I'm even on the right track.

I would like to clarify that the classical approach to the photoelectric effect is based on the assumption that light is a wave and energy is transferred continuously. However, according to quantum mechanics, light is made up of discrete packets of energy called photons. The photoelectric effect cannot be explained using the classical approach and requires the understanding of the quantum nature of light.

Now, to address the given problem, assuming a point source of light with an energy output of 3 watts, the light intensity can be calculated using the formula I = E/(area*time). This gives a value of 4.68x10^18 ev/m^2*s.

For part b, we need to consider the reasonable size of an atom (10^-10 m) and the energy/time incident on the atom for the given intensity. This can be calculated by dividing the intensity by the surface area of the atom. However, it should be noted that this calculation is based on the classical approach and may not accurately represent the photoelectric effect. A more accurate approach would require the use of quantum mechanics and the understanding of the energy levels of the atom.