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JEE Advanced 2015Paper 2
Exam
JEE Advanced
Year
2015
Paper
Paper 2
Subject
Physics
Chapter
Thermodynamics

JEE Advanced 2015 · Paper 2 · Physics · Thermodynamics

An ideal monoatomic gas is confined in a horizontal cylinder by a...

An ideal monoatomic gas is confined in a horizontal cylinder by a spring loaded piston (as shown in the figure).Initially the gas is at temperature T1{T}_{1} , pressure P1{P}_{1} and volume V1{V}_{1} and the spring is in its relaxed state. The gas is then heated very slowly to temperature T2{T}_{2} , pressure P2{P}_{2} and volume V2{V}_{2} . During this process the piston moves out by a distance xx . Ignoring the friction between the piston the cylinder, the correct statement(s) is (are)

An ideal monoatomic gas is confined in a horizontal cylinder by a spring loaded piston (as shown in the

Options

  1. AIf V2=2V1{V}_{2} = 2{V}_{1} and T2=3T1{T}_{2} = 3{T}_{1} , then the energy stored in the spring is 14P1V1\dfrac{1}{4}{P}_{1}{V}_{1}
  2. BIf V2=2V1{V}_{2} = 2{V}_{1} and T2=3T1{T}_{2} = 3{T}_{1} , then the change in internal energy is 3P1V13{P}_{1}{V}_{1}
  3. CIf V2=3V1{V}_{2} = 3{V}_{1} and T2=4T1{T}_{2} = 4{T}_{1} , then the work done by the gas is 73P1V1\dfrac{7}{3}{P}_{1}{V}_{1}
  4. DIf V2=3V1{V}_{2} = 3{V}_{1} and T2=4T1{T}_{2} = 4{T}_{1} , then the heat supplied to the gas is 176P1V1\dfrac{17}{6}{P}_{1}{V}_{1}

Correct answer

A. If V2=2V1{V}_{2} = 2{V}_{1} and T2=3T1{T}_{2} = 3{T}_{1} , then the energy stored in the spring is 14P1V1\dfrac{1}{4}{P}_{1}{V}_{1}

Step-by-step solution


An ideal monoatomic gas is confined in a horizontal cylinder by a spring loaded piston (as shown in the

An ideal monoatomic gas is confined in a horizontal cylinder by a spring loaded piston (as shown in the
(i) P=P1+KxAP = {P}_{1} + \dfrac{Kx}{A}
P2=32P1⇒x=V1A{P}_{2} = \dfrac{3}{2}{P}_{1} ⇒ x = \dfrac{{V}_{1}}{A}
3P12=P1+KxA\dfrac{3{P}_{1}}{2} = {P}_{1} + \dfrac{Kx}{A}
Kx=P1A2Kx = \dfrac{{P}_{1}A}{2}
Energy of spring
12Kx2=P1A4x=P1V14\dfrac{1}{2}K{x}^{2} = \dfrac{{P}_{1}A}{4}x = \dfrac{{P}_{1}{V}_{1}}{4}
(ii) ∆U=f2(P2V2−P2V1)∆ U = \dfrac{f}{2}\left({P}_{2}{V}_{2} - {P}_{2}{V}_{1}\right)
=3P1V1= 3{P}_{1}{V}_{1}
(iii) Pf=4P13{P}_{f} = \dfrac{4{P}_{1}}{3}
KX=P13AKX = \dfrac{{P}_{1}}{3}A
X=2V1AX = \dfrac{2{V}_{1}}{A}
Wgas=−(WPatm+Wspring){W}_{gas} = - \left({W}_{{P}_{atm}} + {W}_{spring}\right)
=(P1Ax+12Kx.x)= \left({P}_{1}Ax + \dfrac{1}{2}Kx . x\right)
=+(P1A.2V1A+12.P1A3.2V1A)= + \left({P}_{1}A . \dfrac{2{V}_{1}}{A} + \dfrac{1}{2} . \dfrac{{P}_{1}A}{3} . \dfrac{2{V}_{1}}{A}\right)
=2P1V1+P1V13=7P1V13= 2{P}_{1}{V}_{1} + \dfrac{{P}_{1}{V}_{1}}{3} = \dfrac{7{P}_{1}{V}_{1}}{3}
(iv) ∆Q=W+∆U∆ Q = W + ∆ U
=7P1V13+32(P2V2−P1V1)= \dfrac{7{P}_{1}{V}_{1}}{3} + \dfrac{3}{2}\left({P}_{2}{V}_{2} - {P}_{1}{V}_{1}\right)
=7P1V13+32(43P1.3V1−P1V1)= \dfrac{7{P}_{1}{V}_{1}}{3} + \dfrac{3}{2}\left(\dfrac{4}{3}{P}_{1} . 3{V}_{1} - {P}_{1}{V}_{1}\right)
=7P1V13+92P1V1=41P1V16= \dfrac{7{P}_{1}{V}_{1}}{3} + \dfrac{9}{2}{P}_{1}{V}_{1} = \dfrac{41{P}_{1}{V}_{1}}{6}
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