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JEE Main 2020Physics Thermodynamics

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mcq
2020
Official previous-year question

Verified 30 May 2026.

Question

Two moles of an ideal monoatomic gas occupy a volume $2V$ at temperature $300\,\text{K}$. The gas expands adiabatically to a volume $16V$. The temperature of the gas after expansion is approximately:

Options

  1. A

    $150\,\text{K}$

  2. B

    $75\,\text{K}$

  3. C

    $100\,\text{K}$

  4. D

    $120\,\text{K}$

Solution

For adiabatic process: $TV^{\gamma-1} = \text{const}$

For monoatomic gas, $\gamma = \frac{5}{3}$, so $TV^{2/3} = \text{const}$

$$300 \cdot (2V)^{2/3} = T_2 \cdot (16V)^{2/3}$$

$$T_2 = 300 \cdot \left(\frac{2}{16}\right)^{2/3} = 300 \cdot \left(\frac{1}{8}\right)^{2/3} = 300 \cdot \frac{1}{4} = 75\,\text{K}$$

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