Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Advanced 2021Paper 2
Exam
JEE Advanced
Year
2021
Paper
Paper 2
Subject
Physics
Chapter
Thermodynamics

JEE Advanced 2021 · Paper 2 · Physics · Thermodynamics

Paragraph A thermally insulating cylinder has a thermally...

Paragraph
A thermally insulating cylinder has a thermally insulating and frictionless movable partition in the middle, as shown in the figure below. On each side of the partition, there is one mole of an ideal gas, with specific heat at constant volume, CV=2RC_{V}=2 R. Here, RR is the gas constant. Initially, each side has a volume V0V_{0} and temperature T0T_{0}. The left side has an electric heater, which is turned on at very low power to transfer heat QQ to the gas on the left side. As a result the partition moves slowly towards the right reducing the right side volume to V0/2V_{0} / 2. Consequently, the gas temperatures on the left and the right sides become TLT_{L} and TRT_{R}, respectively. Ignore the changes in the temperatures of the cylinder, heater and the partition.
Paragraph A thermally insulating cylinder has a thermally insulating and frictionless movable partition in the middle,
QuestionThe value of QRT0\dfrac{Q}{R{T}_{0}} is:

Options

  1. A4(22+1)4\left(2\sqrt{2} + 1\right)
  2. B4(22−1)4\left(2\sqrt{2} - 1\right)
  3. C(52+1)\left(5\sqrt{2} + 1\right)
  4. D(52−1)\left(5\sqrt{2} - 1\right)

Correct answer

B. 4(22−1)4\left(2\sqrt{2} - 1\right)

Step-by-step solution

Paragraph A thermally insulating cylinder has a thermally insulating and frictionless movable partition in the middle,

Writing CV{C}_{V} in terms of degree of freedom of the gas ff, we get,

CV=f2R=2R⇒f=4,{C}_{V} = \dfrac{f}{2}R = 2R ⇒ f = 4,

Therefore, adiabatic index of gas will be given by,γ=1+2f=1+24=32\gamma = 1 + \dfrac{2}{f} = 1 + \dfrac{2}{4} = \dfrac{3}{2}

The gas of the right portion has undergone through an adiabatic process so,

TiViγ−1=TfVfγ−1⇒T0V032−1=TR(V02)32−1{T}_{i}{V}_{i}^{\gamma - 1} = {T}_{f}{V}_{f}^{\gamma - 1} ⇒ {T}_{0}{V}_{0}^{\dfrac{3}{2} - 1} = {T}_{R}{\left(\dfrac{{V}_{0}}{2}\right)}^{\dfrac{3}{2} - 1}

⇒TR=2T0⇒TRT0=2⇒ {T}_{R} = \sqrt{2}{T}_{0} ⇒ \dfrac{{T}_{R}}{{T}_{0}} = \sqrt{2}

Work done by the gas \left(2\right),,= - ∆ U = - n{C}_{V}\left({T}_{f} - {T}_{i}\right)</p><p></p><p>= - \left(1\right)\left(2R\right)\left(\sqrt{2}{T}_{0} - {T}_{0}\right)</p><p></p><p>= - \left(2\sqrt{2} - 2\right)R{T}_{0}</p><p>Soworkdonebythegas(1)</p><p>So work done by the gas \left(1\right),=+(22−2)RT0= + \left(2\sqrt{2} - 2\right)R{T}_{0}

PV=nRT⇒P∝TVPV = nRT ⇒ P ∝ \dfrac{T}{V}

For gas \left(2\right), T \to \sqrt{2}timesofinitialvalue,Volumetimes of initial value, Volume\to \dfrac{1}{2}timesofinitialvalue</p><p>So,times of initial value</p><p>So,P ∝ \dfrac{\sqrt{2}}{\dfrac{1}{2}} = 2\sqrt{2}timesofinitialvaluetimes of initial value⇒ {P}_{f} = 2\sqrt{2}{P}_{0}</p><p>Sopressureofthegas</p><p>So pressure of the gas( 1 )willalsobewill also be2\sqrt{2}timesandvolumeofgastimes and volume of gas( 1 )becomesbecomes\dfrac{3}{2}times</p><p>times</p><p>T ∝ PV</p><p></p><p>⇒ T ∝ \left(2\sqrt{2}\left(\dfrac{3}{2}\right)\right) = 3\sqrt{2}timesofinitialvalue</p><p>times of initial value</p><p>{T}_{L} = 3\sqrt{2}{T}_{0}</p><p></p><p>∆ Ufortheleftgasfor the left gas= n{C}_{V}\left({T}_{f} - {T}_{i}\right)</p><p></p><p>= \left(1\right)\left(2R\right)\left(3\sqrt{2}{T}_{0} - {T}_{0}\right) = \left(6\sqrt{2} - 2\right)R{T}_{0}</p><p>Heatgiventogas</p><p>Heat given to gas( 1 ),</p><p>,</p><p>Q = W + ∆ U</p><p></p><p>= \left(2\sqrt{2} - 2\right)R{T}_{0} + \left(6\sqrt{2} - 2\right)R{T}_{0}</p><p></p><p>= 4{RT}_{0}\left(2\sqrt{2} - 1\right)</p><p>Therefore,</p><p></p><p>Therefore,</p><p>\dfrac{Q}{R{T}_{0}} = 4\left(2\sqrt{2} - 1\right)

Practice Thermodynamics on Quantrex Academy →

More from Thermodynamics

A quasi-static cycle of a monoatomic ideal gas contains an isothermal process ( ab )… JEE Advanced 2026As shown in the figure, five Carnot engines, each with efficiency η and same number of… JEE Advanced 2026Ten moles of an ideal monoatomic gas, initially in state a at atmospheric pressure and… JEE Advanced 2026One mole of diatomic gas having rotational modes only is kept in a cylinder with a piston… JEE Main 2026Initial pressure and volume of a monoatomic ideal gas are P and V . The change in… JEE Main 2026A cylinder with adiabatic walls is closed at both ends and is divided into two… JEE Main 2026Two closed vessels of same volume are joined through a narrow tube and both vessels are… JEE Main 2026A certain gas is isothermally compressed to ((1)/(3))^ rd of its initial volume ( V_o = 3… JEE Main 2026 Full Thermodynamics list All JEE Advanced PYQs