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JEE Main 20205 SeptemberEvening Shift
Exam
JEE Main
Year
2020
Date
5 September
Shift
Evening Shift
Subject
Physics
Chapter
Thermodynamics

JEE Main 2020 · 5 September · Evening Shift · Physics · Thermodynamics

In an adiabatic process, the density of a diatomic gas becomes 32 n...

In an adiabatic process, the density of a diatomic gas becomes 3232nn times its initial value. The final pressure of the gas is found to be nn times the initial pressure. The value of nn is:

Options

  1. A3232
  2. B326326
  3. C128128
  4. D132\dfrac{1}{32}

Correct answer

C. 128128

Step-by-step solution

Given,

Final density of diatomic gas is ρf=32nρi{ρ}_{f} = 32n{ρ}_{i}

Final pressure is Pf=nPi{P}_{f} = n{P}_{i}

In adiabatic process, equation of state is given by,

PVγ=constant...(1)P{V}^{\gamma} = \text{constant} . . . \left(1\right)

Where, VV is the volume, PP is the pressure and γ=75\gamma = \dfrac{7}{5} is the ratio of specific heat of diatomic gas

P(mρ)γ=constant...(2)P{\left(\dfrac{m}{ρ}\right)}^{\gamma} = \text{constant} . . . \left(2\right), As V=mρV = \dfrac{m}{ρ}

and mass is constant, then the pressure is given by

∴P∝ργ∴ P ∝ {ρ}^{\gamma}

⇒PfPi=(ρfρi)γ⇒ \dfrac{{P}_{f}}{{P}_{i}} = {\left(\dfrac{{ρ}_{f}}{{ρ}_{i}}\right)}^{\gamma}

⇒nPiPi=(32ρiρi)7/5=(32)7/5⇒ \dfrac{n{P}_{i}}{{P}_{i}} = {\left(\dfrac{32{ρ}_{i}}{{ρ}_{i}}\right)}^{{}^{7 / 5}} = ( 32{)}^{7 / 5}

∴n=27=128∴ n = {2}^{7} = 128

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