The mean free path for a gas,with molecular diameter $d$ and number density $n$,can be expressed as:

Ten small planes are flying at a speed of $150 \ km/h$ in total darkness in an air space that is $20 \times 20 \times 1.5 \ km^3$ in volume. You are in one of the planes, flying at random within this space with no way of knowing where the other planes are. On the average, about how long a time will elapse between near collisions with your plane? Assume for this rough computation that a safety region around the plane can be approximated by a sphere of radius $10 \ m$.

If the diameter of a gas molecule is very small,what will be the mean free path?

The mean free path and the average speed of oxygen molecules at $300 \ K$ and $1 \ atm$ are $3 \times 10^{-7} \ m$ and $600 \ m/s$,respectively. Find the frequency of its collisions.

Under what conditions does a real gas obey the relation $PV = RT$?

The value of critical temperature in terms of van der Waals' constants $a$ and $b$ is given by