AIIMS 2018 Physics First Law of Thermodynamics MCQ Question
One monatomic gas is expanded adiabatically from 2 L to 10 L at 1 atm external pressure, find ΔU (in atm L)?
−8
0
−66.7
58.2
Correct Answer
Detailed Explanation
In an adiabatic expansion of a monatomic gas, the change in internal energy (ΔU) is equal to the work done on the gas, which is negative during expansion. The work done (W) can be calculated using the formula W = -PΔV; here, ΔV = V_final - V_initial = 10 L - 2 L = 8 L, and P = 1 atm, resulting in W = -1 atm × 8 L = -8 atm L. Thus, ΔU = W = -8 atm L.
Option B (0) is incorrect because it assumes no change in internal energy, which contradicts the work done during expansion. Options C (−66.7) and D (58.2) do not align with the calculated work and internal energy change for this adiabatic process.
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