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Interstellar space has an average temperature of about 10K and an average density of hydrogen atoms of about one hydrogen atom per cubic meter. Compute the main free path of a hydrogen atom in interstellar space. Take the diameter of an H atom to be 100 pm.

Here is what I did. I first calculated the density.

Density =(pressure)(Na)/RT=(1x10^-11)*(6.022E22)/(8.314*10) = 7.243 E10 m^-3

(I used 1x10^-11 for the pressure in space)

The I used this to find the MFP.

lamda = 1/(root(2)*density*pi*d^2) = 1/(root(2)*7.243E10*pi*(100x10^-12)^2)

So for the mean free path I got .310 nm.

Can someone verify if this is correct.

thanks

nertil