Assumptions of kinetic theory and the concept of pressure — NEET & JEE Questions

Question 1 · difficulty L1 · recall

In the kinetic theory of an ideal gas, gas molecules are assumed to be

• A. point particles in continuous random motion
• B. at rest except during collisions
• C. strongly attracting one another at all distances
• D. fixed at lattice points

Question 2 · difficulty L2 · understanding

Which assumption is made about intermolecular forces in an ideal gas?

• A. They are negligible except during collisions
• B. They are always strongly attractive
• C. They are always strongly repulsive
• D. They keep every molecule at fixed separation

Question 3 · difficulty L2 · understanding

Collisions between ideal-gas molecules and the container walls are assumed to be

• A. perfectly elastic
• B. perfectly inelastic
• C. absent
• D. chemical reactions

Question 4 · difficulty L2 · understanding

Gas pressure on the walls of a container arises mainly from

• A. momentum transfer during molecular collisions with the walls
• B. the weight of the container
• C. attractive force between opposite walls
• D. the colour of the gas

Question 5 · difficulty L3 · application

If the number of gas molecules per unit volume increases while their mean square speed remains unchanged, the gas pressure should

• A. increase
• B. decrease
• C. remain unchanged
• D. become zero

Question 6 · difficulty L3 · application

For an ideal gas, which expression relates pressure P, density $\rho$ and mean square molecular speed $\langle c^2\rangle$?

• A. $P=\frac13\rho\langle c^2\rangle$
• B. $P=3\rho\langle c^2\rangle$
• C. $P=\frac{\rho}{3\langle c^2\rangle}$
• D. $P=\rho\langle c\rangle$

Question 7 · difficulty L3 · application

A gas molecule strikes a wall normally and reverses its velocity from +v to -v. The magnitude of its momentum change is

• A. $2mv$
• B. $mv$
• C. $mv/2$
• D. 0

Question 8 · difficulty L3 · application

If all molecular speeds in an ideal gas were doubled while density remained fixed, kinetic theory predicts pressure would become

• A. four times
• B. twice
• C. half
• D. unchanged

Question 9 · difficulty L4 · application

Two ideal gases have the same density. Gas P has twice the RMS speed of gas Q. What is the ratio $P_P/P_Q$?

• A. 4
• B. 2
• C. 1/2
• D. 1/4

Question 10 · difficulty L4 · application

Why does a gas exert pressure equally in all directions in equilibrium?

• A. Molecular motion is random and isotropic on average
• B. All molecules move only along one axis
• C. Gravity makes all wall collisions identical
• D. The walls pull molecules equally