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JEE Main202117 Mar 2021Morning ShiftPhysicsKinetic Theory of GasesActual

Two ideal polyatomic gases at temperatures T 1 and T 2 are mixed so that there is no loss of energy. If F 1 and F 2 , m 1 and m 2 , n 1 and 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. An 1   T 1 + n 2   T 2 n 1 + n 2
  2. Bn 1 F 1 T 1 + n 2 F 2 T 2 n 1 F 1 + n 2 F 2
  3. Cn 1   F 1   T 1 + n 2   F 2   T 2   F 1 + F 2
  4. Dn 1   F 1   T 1 + n 2   F 2   T 2 n 1 + n 2

Correct answer

B. 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 . Since, there is no loss in energy. Δ U = 0 ⇒ F 1 2 n 1 R Δ T + F 2 2 n 2 R Δ T = 0 ⇒ F 1 2 n 1 R T 1 - T + F 2 2 n 2 R T 2 - T = 0 ⇒ T = F 1 n 1 R T 1 + F 2 n 2 R T 2   F 1 n 1 R + F 2 n 2 R = F 1 n 1   T 1 + F 2 n 2   T 2   F 1 n 1 + F 2 n 2

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