Physics Thermodynamics NUMS 2023
PMDC Verified Question 29 of 54
If 42 J heat is transferred to the system during expansion, what is the change in internal energy when work done is 32 J?
A
106 J
B
10 J
C
116 J
D
74 J
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 10 J
1. Concept:

The First Law of Thermodynamics operates as an energy balance sheet: Energy In (Heat) minus Energy Out (Work) equals Energy Stored (Internal Energy).

2. Formula:

$$\Delta U = Q - W$$

3. Solution:

  • Heat transferred INTO the system is positive: \(Q = +42 \text{ J}\).


  • Work done BY the system during expansion is positive: \(W = +32 \text{ J}\).


  • Apply the equation: \(\Delta U = 42 - 32\).


  • The net change in internal energy is \(\Delta U = +10 \text{ J}\).


4. Why other options are incorrect:

Adding the numbers yields 74 J, which incorrectly assumes work was done ON the system (compression) rather than BY the system (expansion).

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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