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Q & A: Multi-step production of photelectric effect?

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Most recent answer: 04/09/2010
Q:
hi ok the q i have is .......... we are knowing that photoelectric current produced in the process of photoelectric does not depend on the intensity till it less than the threshold frequency.............. but i'll give u an example which wen compared with this shows contradiction........... ok..suppose there is a ditch (full of muddy water)with a ball in it.... and there are three ..4 ppl standing by its side...... 1st person kicks the ball with less than the required energy and the ball bounces up..... not goes out of the ditch........ ok as soon as the ball is lifted above the water the 2nd person kicks it with almost the same energy.....and the rest 2 follow the same process..... now how much is the probability that the ball come out of the ditch.. and if the no. of ppl or rays in the original case r increased then of course the chances increase .............. but this is not observed with the photoelectric effect........... hope the comparsion was understandable........ so wat factors r prompt not to let this happen.... i mean there is no problem of time lag............as the speed of light is too high with which sped em wave stravel......... still no result like this.... wanna hear ur opinion on this and discuss it with u....... and it cannot be called thermopile emission of electron as the metal 's (photosensitive ).. electron are supposed to be knocked out before causing production of heat....... thanks for ur time....... waiting for ur reply.......
- apoo (age 17)
india
A:
Hi Apoo,
I really like your ball-in-the-ditch analogy of multiple excitation of photo-electrons.  This kind of process actually occurs and its study is useful in determining many properties of semiconductor materials.   The major difference between the multi-step process and the ordinary photoelectric effect is the dependence of the number of ejected photo-electrons on the incident intensity.  In the ordinary case the dependence is linear.  In the case of, say two-step processes, the dependence would be quadratic, etc.     You do need a time lag in the process in order that a second or third photon can finally kick the electron out.  This is provided by an excited state in the atomic system that is long lived.  You can Google "multiphoton photoexcitation" and find many papers on the subject.

LeeH

(published on 04/09/2010)

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