Verified Solution • 2025–26 Session moderate

QJEEAdv23Ph2e5a: JEE Advanced 2023 Physics - Class 11 JEEAdv23Ph2e5a Solution: An ideal gas is in thermodynamic equilibrium. The number of…

An ideal gas is in thermodynamic equilibrium. The number of degrees of freedom of a molecule of the gas is nn . The internal energy of one mole of the gas is UnU_n and the speed of sound in the gas is vn\mathrm{v}_n . At a fixed temperature and pressure, which of the following is the correct option?

Multiple Choice Options

  • A v3<v6v_3 < v_6 and U3>U6U_3 > U_6
  • B v5>v3v_5 > v_3 and U3>U5U_3 > U_5
  • C v5>v7v_5 > v_7 and U5<U7U_5 < U_7
  • D v6<v7v_6 < v_7 and U6<U7U_6 < U_7

Step-by-Step Verified Solution

1. Formula for Sound Velocity:

- The velocity of sound, denoted as v, is determined by the equation v=γRTM, where:

- γ is a factor given by γ=1+2n.

- R is the gas constant.

- T is the temperature.

- M is the molar mass of the gas.

2. Relation of γ with n:

- The value of γ is inversely related to n. This means as n increases, γ decreases.

3. Internal Energy Relation:

- The internal energy, denoted as U, for a mole of gas is given by U=nRT2.

4. Effect of Increasing n on Sound Velocity and Internal Energy:

When the value of n increases:

- The factor γ decreases, according to its formula.

- As a result, the velocity of sound v also decreases, as it is dependent on γ.

- Conversely, the internal energy Un increases with the increase in n, as evident from the internal energy formula.

Therefore, in summary, a higher value of n leads to a lower velocity of sound and higher internal energy in the context of these formulas.

Related Learning Resources & Exam Preparation