Q120 / 150 · MHT CET 2026 (17 April Shift 2) · Physics
A thermodynamic system is compressed adiabatically, then its temperature
- Abecomes zero.
- Bremains constant.
- Correct answerCincreases.
- Ddecreases.
Solution
In an adiabatic process, there is no heat exchange with the surroundings, so $dQ = 0$.
According to the first law of thermodynamics, $dQ = dU + dW$.
Substituting $dQ = 0$, we get $dU = -dW$.
During compression, work is done on the system, which means the work done by the system $dW$ is negative ($dW < 0$).
Therefore, $dU = -(-\text{positive value}) > 0$.
Since the internal energy $U$ increases and internal energy is directly proportional to temperature ($dU = nC_v dT$), the temperature of the system increases.
According to the first law of thermodynamics, $dQ = dU + dW$.
Substituting $dQ = 0$, we get $dU = -dW$.
During compression, work is done on the system, which means the work done by the system $dW$ is negative ($dW < 0$).
Therefore, $dU = -(-\text{positive value}) > 0$.
Since the internal energy $U$ increases and internal energy is directly proportional to temperature ($dU = nC_v dT$), the temperature of the system increases.
Hence, the correct answer is option: 'C'.