Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Probabilities and binomial theorem

  1. Sep 27, 2011 #1
    1. The problem statement, all variables and given/known data

    Consider an ideal gas of N identical particles in a volume V, and a subvolume v. The chance a molecule is in inside the subvolume is P = v/V.

    a) What is the chance the subvolume contains n particles?

    b) Use the binomial theorem [tex](p + q)^N = \sum_{n = 0}^N p^n q^{N-n} \frac{N!}{n!(N-n)!}[/tex] for random p and q to calculate the average number of particles [tex]\langle n\rangle[/tex] and the variance [tex]\sigma^2 = \langle n^2 \rangle - \langle n \rangle^2[/tex]

    Anyone who could give me a nudge in the right direction?
  2. jcsd
  3. Sep 27, 2011 #2
    As the gas is ideal, the particles can go inside the subvolume independently. Thus, the answer is (v/V)^N =p^N. Part (b) follows from straightforward but long calculations.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook