Physics Thermodynamics PMDC 2020
PMDC Verified Question 46 of 54
The internal energy of a system during an isothermal process:
A
Decreases
B
Remain constant
C
Become zero
D
Increases
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Remain constant
1. Concept:

For an ideal gas, the internal energy is directly proportional to its absolute temperature.

2. Formula:

$$U \propto T \implies \Delta U = n C_v \Delta T$$

3. Solution:

  • An isothermal process is defined as a thermodynamic change where the temperature remains constant (\(\Delta T = 0\)).


  • Since the change in temperature is zero, the change in internal energy \(\Delta U\) is also zero.


  • Hence, the internal energy remains completely constant throughout the process.


4. Why other options are incorrect:

Internal energy would increase during heating (temp rise) and decrease during cooling (temp fall), but cannot change if temperature is locked.

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