JEE MAIN - Physics (2025 - 23rd January Morning Shift - No. 25)
Explanation
We’re given an ideal gas initially at $$T_i = 0^\circ \mathrm{C} = 273\,\mathrm{K}.$$ The gas is suddenly compressed to one-fourth of its initial volume, and we are told that
$$\gamma = \frac{c_p}{c_v} = \frac{3}{2}\,.$$
For an adiabatic process (one in which there is no heat exchange), if the process were reversible, the relation between the temperature and volume would be
$$T\, V^{\gamma-1} = \text{constant}\,.$$
Even though the compression is “sudden” (and hence irreversible), the final equilibrium state of the gas is uniquely determined by its internal energy (which is a state function). That allows us to use the adiabatic relation between the initial and final states.
Here are the steps:
Write the adiabatic relation between the initial and final states:
$$T_i\, V_i^{\gamma-1} = T_f\, V_f^{\gamma-1}\,.$$
Since the gas is compressed to one-fourth of its volume, we have
$$V_f = \frac{1}{4} V_i\,.$$
Substitute this into the adiabatic relation:
$$273\,V_i^{\gamma-1} = T_f \left(\frac{1}{4} V_i\right)^{\gamma-1}\,.$$
With $$\gamma = \frac{3}{2},$$
$$\gamma - 1 = \frac{3}{2} - 1 = \frac{1}{2}\,.$$
So the relation becomes:
$$273\,V_i^{1/2} = T_f \left(\frac{1}{4}\right)^{1/2} V_i^{1/2}\,.$$
Cancel the common factor $$V_i^{1/2}$$ (provided it is nonzero) and simplify:
$$273 = T_f \left(\frac{1}{2}\right)\,.$$
Now solve for the final temperature $$T_f$$:
$$T_f = 273 \times 2 = 546\,\mathrm{K}\,.$$
The change in temperature is then:
$$\Delta T = T_f - T_i = 546 - 273 = 273\,\mathrm{K}\,.$$
So, the change in temperature due to the thermodynamic process is $$\boxed{273\,\mathrm{K}}.$$
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