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NEET 2026 (Re-neet) · Specific Heats of Gases - Cp, Cv, γ & Mayer's Relation

Specific Heats of Gases - Cp, Cv, γ & Mayer's Relation question from NEET 2026 (Re-neet)

Q8NEET 2026 · RE-NEETMedium

Specific Heats of Gases - Cp, Cv, γ & Mayer's Relation

An ideal gas is made of polyatomic molecules. Each of the molecules has three translational, three rotational and $f$ number of vibrational modes. If the ratio of heat capacities $C_P/C_V$ of the gas is $8/7$ , then the value of $f$ is:

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Answer: (b)

Translation + rotation: $6 \times \dfrac{1}{2}R = 3R$ ; each vibrational mode adds $R$ .
$C_V = (3 + f)R$ , $C_P = (4 + f)R$ .
$\dfrac{4+f}{3+f} = \dfrac{8}{7} \Rightarrow 28 + 7f = 24 + 8f \Rightarrow f = 4$
So the answer is (b) 4.

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