Mean Free Path MCQ - Practice Questions with Answers

Mean Free Path - 

On the basis of kinetic theory of gases, it is assumed that the molecules of a gas are continuously colliding against each other. So, the distance travelled by a gas molecule between any two successive collisions is known as free path.

There are assumption for this theory that during two successive collisions, a molecule of a gas moves in a straight line with constant velocity. Now, let us discuss the formula of mean free path - 

Let   be the distance travelled by a gas molecule during n collisions respectively, then the mean free path of a gas molecule is defined as - 

Here,  is the mean free path.

It can also be written as -        

Now, let us take d = Diameter of the molecule,
                          N = Number of molecules per unit volume.

Also, we know that,  PV = nRT 

So, Number of moles per unit volume  =  

Also we know that number of molecules per unit mole  =  

So, the number of molecules in 'n' moles = nN_A

So the number of molecules per unit volume is   

                                                                 So, 

If all the other molecules are not at rest then, 

Now, if    and m = mass of each molecule then we can write - 

                                                                        So,