Hi! We'd been thinking with a bunch of friends for a couple of days, but eventually came up with nothing. Hence my question. The exercise seems to be quite simple: Given that the probability of one electron being (thermo)emitted form a surface of a metal in an inifinitively short period of time is A*dt, A being constant, and that each two emissions are statistically independant, calculate the probability of n electrons being emitted over a period of time t. First idea was just to integrate A*dt from 0 to t to get the probability of one electron being emitted, but with A being constant one would eventually end up with the probability >1, which is total rubbish. Unfortunately, no other ideas showed up since tuesday ;). I myself would definityely expect a probability denisty function that would asymptotically drift towards a value of one, never to reach it. However, the other idea that also makes sense to me is the probability being constant for the whole time, with the value of A. In example, if the probability of winning in a lottery is 1/700, then it doesn't matter how many times you try, it will always remain the same (playing 4 times gives you 4 chances over 2800, which is 1/700 again). Having said that, though, I don't understand the "dt" part :). Certainly, the probability of n electrons being emitted is p^n, p being the probability of one electron being emitted. Thanks in advance for your help.