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JEE Main 202117 MarchMorning Shift
Exam
JEE Main
Year
2021
Date
17 March
Shift
Morning Shift
Subject
Physics
Chapter
Kinetic Theory of Gases

JEE Main 2021 · 17 March · Morning Shift · Physics · Kinetic Theory of Gases

Two ideal polyatomic gases at temperatures T _ 1 and T _ 2 are...

Two ideal polyatomic gases at temperatures T1{T}_{1} and T2{T}_{2} are mixed so that there is no loss of energy. If F1{F}_{1} and F2,m1{F}_{2}, {m}_{1} and m2,n1{m}_{2}, {n}_{1} and n2{n}_{2} be the degrees of freedom, masses, number of molecules of the first and second gas respectively, the temperature of mixture of these two gases is:

Options

  1. An1T1+n2T2n1+n2\dfrac{{n}_{1}{T}_{1} + {n}_{2}{T}_{2}}{{n}_{1} + {n}_{2}}
  2. Bn1F1T1+n2F2T2n1F1+n2F2\dfrac{{n}_{1}{F}_{1}{T}_{1} + {n}_{2}{F}_{2}{T}_{2}}{{n}_{1}{F}_{1} + {n}_{2}{F}_{2}}
  3. Cn1F1T1+n2F2T2F1+F2\dfrac{{n}_{1}{F}_{1}{T}_{1} + {n}_{2}{F}_{2}{T}_{2}}{{F}_{1} + {F}_{2}}
  4. Dn1F1T1+n2F2T2n1+n2\dfrac{{n}_{1}{F}_{1}{T}_{1} + {n}_{2}{F}_{2}{T}_{2}}{{n}_{1} + {n}_{2}}

Correct answer

B. n1F1T1+n2F2T2n1F1+n2F2\dfrac{{n}_{1}{F}_{1}{T}_{1} + {n}_{2}{F}_{2}{T}_{2}}{{n}_{1}{F}_{1} + {n}_{2}{F}_{2}}

Step-by-step solution

Let the final temperature of the mixture be T.T .

Since, there is no loss in energy.

\DeltaU=0\DeltaU = 0

⇒F12n1R\DeltaT+F22n2R\DeltaT=0⇒ \dfrac{{F}_{1}}{2}{n}_{1}R\DeltaT + \dfrac{{F}_{2}}{2}{n}_{2}R\DeltaT = 0

⇒F12n1R(T1−T)+F22n2R(T2−T)=0⇒ \dfrac{{F}_{1}}{2}{n}_{1}R\left({T}_{1} - T\right) + \dfrac{{F}_{2}}{2}{n}_{2}R\left({T}_{2} - T\right) = 0

⇒T=F1n1RT1+F2n2RT2F1n1R+F2n2R=F1n1T1+F2n2T2F1n1+F2n2⇒ T = \dfrac{{F}_{1}{n}_{1}R{T}_{1} + {F}_{2}{n}_{2}R{T}_{2}}{{F}_{1}{n}_{1}R + {F}_{2}{n}_{2}R} = \dfrac{{F}_{1}{n}_{1}{T}_{1} + {F}_{2}{n}_{2}{T}_{2}}{{F}_{1}{n}_{1} + {F}_{2}{n}_{2}}

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