Question:

An ideal gas is expanding such that \[ P^2T=\text{constant}. \] The coefficient of volume expansion of the gas is \[ (P=\text{Pressure},\; T=\text{Temperature}) \]

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If \[ V\propto T^n, \] then \[ \alpha = \frac{1}{V}\frac{dV}{dT} = \frac{n}{T}. \] Here, \[ V\propto T^{3/2}, \] hence \[ \alpha=\frac{3}{2T}. \]
Updated On: Jul 9, 2026
  • \(\dfrac{1}{T}\)
  • \(\dfrac{2}{T}\)
  • \(\dfrac{3}{T}\)
  • \(\dfrac{3}{2T}\) \bigskip
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The Correct Option is D

Solution and Explanation

Concept: The coefficient of volume expansion is defined as \[ \alpha = \frac{1}{V} \left(\frac{\partial V}{\partial T}\right). \] For an ideal gas, \[ PV=nRT. \]

Step 1:
Use the given condition. Given, \[ P^2T=\text{constant}. \] Therefore, \[ P^2=\frac{k}{T}, \] where \(k\) is a constant. Hence, \[ P=\frac{\sqrt{k}}{\sqrt{T}} \propto T^{-1/2}. \]

Step 2:
Express volume in terms of temperature. Using the ideal gas equation, \[ V=\frac{nRT}{P}. \] Since \[ P\propto T^{-1/2}, \] we get \[ V\propto T\times T^{1/2}. \] \[ V\propto T^{3/2}. \] Let \[ V=C\,T^{3/2}, \] where \(C\) is a constant.

Step 3:
Differentiate with respect to temperature. \[ \frac{dV}{dT} = \frac{3}{2}CT^{1/2}. \] Therefore, \[ \alpha = \frac{1}{CT^{3/2}} \left(\frac{3}{2}CT^{1/2}\right). \] \[ \alpha = \frac{3}{2T}. \]

Step 4:
Write the final answer. \[ \boxed{\alpha=\frac{3}{2T}} \] \[ \boxed{\text{Answer = (D)}} \]
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