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NEET PHYSICSKinetic TheoryMedium

Question

The value γ=CPCV\gamma = \frac{C_P}{C_V} for hydrogen, helium, and another ideal diatomic gas XX (whose molecules are not rigid but have an additional vibrational mode), are respectively equal to:

A

75,53,97\frac{7}{5}, \frac{5}{3}, \frac{9}{7}

B

53,75,97\frac{5}{3}, \frac{7}{5}, \frac{9}{7}

C

53,75,75\frac{5}{3}, \frac{7}{5}, \frac{7}{5}

D

75,53,75\frac{7}{5}, \frac{5}{3}, \frac{7}{5}

Step-by-Step Solution

  1. Formula for γ\gamma: The adiabatic index is given by γ=1+2f\gamma = 1 + \frac{2}{f}, where ff is the number of degrees of freedom.
  2. Hydrogen (H2H_2): It is a diatomic gas. At ordinary temperatures, it behaves as a rigid rotator with f=3f = 3 (translational) +2+ 2 (rotational) =5= 5. γH2=1+25=75\gamma_{H_2} = 1 + \frac{2}{5} = \frac{7}{5}.
  3. Helium (HeHe): It is a monoatomic gas. It has only translational degrees of freedom, so f=3f = 3. γHe=1+23=53\gamma_{He} = 1 + \frac{2}{3} = \frac{5}{3}.
  4. Gas XX: It is a diatomic gas with an additional vibrational mode. A vibrational mode contributes 2 degrees of freedom (potential + kinetic energy) per mode. Thus, f=3f = 3 (translational) +2+ 2 (rotational) +2+ 2 (vibrational) =7= 7. γX=1+27=97\gamma_{X} = 1 + \frac{2}{7} = \frac{9}{7}.
  5. Conclusion: The respective values are 75,53,97\frac{7}{5}, \frac{5}{3}, \frac{9}{7}.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from Kinetic Theory. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSKinetic Theoryfraccpcvhydrogenheliumanotherdiatomic

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