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**wave problem??**

## Homework Statement

An apparatus is used to prepare an atomic beam by heating a collection of atoms to a temperature T and allowing the beam to emerge through a hole of diameter d in one side of the oven. The beam then travels through a straight path of length L. Show that the diamter of the beam at the end of the path is larger than d by an amount of order L*hbar/(d*sqrt(3mkT)) where m is the mass of an atom. Make a numerical estimate for typical values of T=1500K m=7amu(lithium atoms), d=3mm, L=2m.

## Homework Equations

no clue

## The Attempt at a Solution

I calculated the ratio using the given data and got 2.604*10^-9 meters.

I have no clue where to even begin on this problem. Really all I'm looking for is a hint. Not someone to do it for me.