# No clue

1. Jan 23, 2005

### jbot2222

i dont know how to do this...nothing comes to mind. any help will be appreciated!

A pressure as low as 4×10-11Pa has been obtained. Suppose a chamber contains helium at this pressure and at temperature 380K. Estimate the collision time (tau) for helium in the chamber. Take the diameter of a helium molecule to be 1×10-10m.

2. Jan 23, 2005

### dextercioby

Do u know the formula giving the mean free path ($\lambda$)??If so,combine it with the thermal velocity to find the mean collision time...

Daniel.