JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Heat & Thermodynamics

According to kinetic theory of gases,
A. The motion of the gas molecules freezes at

0^{\circ} C

B. The mean free path of gas molecules decreases if the density of molecules is increased.
C. The mean free path of gas molecules increases if temperature is increased keeping pressure constant.
D. Average kinetic energy per molecule per degree of freedom is

\frac{3}{2} k_{B} T

(for monoatomic gases)

Choose the most appropriate answer from the options given below:

(A)A and C only
(B)B and C only✓ Correct
(C)A and B only
(D)C and D only

Answer: (B)

Solution

Statement A is false: molecular motion freezes at absolute zero (−273°C), not 0°C. Statement B is true: mean free path

λ \propto \frac{1}{n}

where

n

is number density; higher density means shorter mean free path. Statement C is true:

λ = \frac{k T}{2 π d ^{2} P}

; at constant P,

λ \propto T

. Statement D is false: average KE per degree of freedom is

\frac{1}{2} k_{B} T

, not

\frac{3}{2} k_{B} T

. Therefore B and C are correct.

JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Single correct option

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JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Heat & Thermodynamics

Solution

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