Kinetic Theory - Online Test

Q1.

If there are n number of molecules per unit volume and m is the mass of each ,  is the x-component of velocity, pressure can be written as


Answer : Option B
Explaination / Solution:

Pressure is due to collision of molecule with the wall of container.

Collision by moleculeto the wall of conntainer assumed to be perfectly elastic.

By the principle of conservation of momentum, the momentum imparted to the wall in the collision = 2mvx 

 the number of molecules hitting the wall in time  = 

n  = no. of molecule per unit volume

A = Area of container

The total momentum transferred to the wall by these molecules in   time = 

Pressure P = F/A = rate of momentum transfer per unit area


all molecules in a gas do not have the same velocity; there is a distribution in velocities. The  above equation therefore, stands for pressure due to the group of molecules with speed vx   in  the x-direction and n stands for the number density of that group of molecules. The total pressurer due to  all  groups 


 


Q2. The average kinetic energy of a molecule
Answer : Option A
Explaination / Solution:

 
E=32kT

ET

Q3. According to the law of equipartition of energy, the total energy is equally distributed in all possible energy modes, with each mode having an average energy equal to
Answer : Option C
Explaination / Solution:

The law of equipartition of energy sates that for any dynamical system in a thermal equilibrium, the total energy is equally divided among the degrees of freedom. The energy associated with a molecule for one degree of freedom is 
Q4. The number of degrees of freedom a diatomic molecule is
Answer : Option B
Explaination / Solution:

Degrees of freedom of a system refers to the possible independent motions a system can have. the total degrees of freedom describing the motion of a diatomic molecule is 5. 3 for translation and 2 for rotation

Q5. The number of degrees of freedom a monatomic molecule is
Answer : Option A
Explaination / Solution:

Degrees of freedom of a system refers to the possible independent motions a system can have. Monoatomic gas molecule can have 3 independent motion and hence have 3 degrees of freedom (all are translational).

Q6. The molar specific heat at constant volume,  for monatomic gases is
Answer : Option B
Explaination / Solution:


for monatomic gases f = 3


Q7. The molar specific heat at constant volume,  for diatomic gases is
Answer : Option C
Explaination / Solution:


for diatomic gases f = 5


Q8.

For a rope of yield strength  loaded in tension with weight Mg the minimum area A of the rope should be


Answer : Option C
Explaination / Solution:

We know that Yield strength times the Area give the weight of the body.

As Yield strength = weight of body/area

For safety purposes

Yield strength  weight of body/area 

  Mg/A

Mg/ 


Q9. Mean free path is the
Answer : Option D
Explaination / Solution:

the mean free path is the average distance traveled by a moving particle (such as an atom, a molecule, a photon) between successive impacts (collisions), which modify its direction or energy or other particle properties.

Q10. Estimate the fraction of molecular volume to the actual volume occupied by oxygen gas at STP. Take the diameter of an oxygen molecule to be 3A 
Answer : Option C
Explaination / Solution:

Radius =  

molecular volume of oxygen 


Actual volume of oxygen at STP = 22400cm3

ratio of molercular volume to the actual volume =