A formula for estimating the mean free path of a perfect gas is: l=1.26- μ p√(RT) -=1.26√(RT) P 'where the latter form follows from the ideal-gas law, p=p/RT. What are the dimensions of the constant "1.26"? Estimate the mean free path of air at 20°C and 7 kPa. Is air rarefied at this condition?