# Gas impingement flux, problem in substituting constants

1. Mar 22, 2013

### jjshan

1. The problem statement, all variables and given/known data
gas impingement flux density is given by ∅=P/$\sqrt{}2mkT$
where m- mass of a molecule

show that
∅=3.513*1022P/$\sqrt{}MT$
where pressure in torr and M-molar mass of molecule
then ∅ in molecules per cm2 per second

2. Relevant equations

∅=3.513*1022P/$\sqrt{}MT$
where pressure in torr and M-molar mass of molecule
then ∅ in molecules per cm2 per second

3. The attempt at a solution

i substitute 1/133 to change pressure scale to torr and multiply by square root of Avogadro no and divide it by square root of 2∏k but i couldn't get appropriate constant. how derive the equation in given scale?

2. Mar 22, 2013

### TSny

It looks like you left out a factor of $\pi$ in the square root of the equation.

Consider:

What are the units of ∅ in the SI system?

What are the units of m in SI system?

What are the units of M?