From the scattering of sunlight, J.J. Thomson estimated the radius of an electro

Question

From the scattering of sunlight, J.J. Thomson estimated the radius of an electron to be 2.82 middot 10^-15 m. (This is now called the classical electron radius.) If sunlight with an intensity of 500 W/m^2 falls on a disk of this radius, estimate the time required for the disk to absorb 1 eV of energy. Treat the light as a classical electromagnetic wave, and assume all the light that strikes the disk is absorbed, How does your estimate from part a) compare with the experimental observation that photoelectrons are emitted within 1 ns of exposure?

Explanation / Answer

intensity, I = 500W/m^2
area, A = pir^2 = pi*(2.82*10^-15)^2 = 2.497*10^-29 m^2
Power = IA = 1.2485*10^-26 W = Et ( E is energy, t is time)
E = 1 eV = 1.6*10^-19 J
t = 7.80329*10^-8 s

this means phortoelectrons cannot be ejected for exposure below 7.8*10^-8 s, but electrons are ejected for 1 ns exposure which is smaller than this. this goes on to show how wave theory cannot predict the results of photoelectric effect and how particle theory is required

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