Verified Solution • 2025–26 Session moderate

QJEEM20Ph57c1: JEE Main 2020 Physics - Class 11 JEEM20Ph57c1 Solution: Molecules of an ideal gas are known to have three translational …

Molecules of an ideal gas are known to have three translational degrees of freedom and two rotational degrees of freedom.The gas is maintained at a temperature of T. The total internal energy, U of a mole of this gas, and the value of
γ(=CpCv)\gamma \left( { = {{{C_p}} \over {{C_v}}}} \right) are given, respectively by:

Multiple Choice Options

  • A U = 52RT{5 \over 2}RT and γ=75\gamma = {7 \over 5}
  • B U = 5RT and γ=65\gamma = {6 \over 5}
  • C U = 5RT and γ=75\gamma = {7 \over 5}
  • D U = 52RT{5 \over 2}RT and γ=65\gamma = {6 \over 5}

Step-by-Step Verified Solution

Total degree of freedom (f) = 3 + 2 = 5

U = nfRT2{{nfRT} \over 2} = 5RT2{{5RT} \over 2}

γ\gamma = CpCv{{{C_p}} \over {{C_v}}} = 1+2f1 + {2 \over f} = 1+251 + {2 \over 5} = 75{7 \over 5}

Related Learning Resources & Exam Preparation

JEE Main PYQ Question Bank
Browse year-wise authentic previous years' questions with solutions
Authentic CBT Mock Tests
Simulate official exam environment with live timer and percentile scoring