Verified Solution • 2025–26 Session moderate

QPages 139-140: Q6: HC Verma: Concepts of Physics - Volume 2 Gauss's Law Pages 139-140: Q6 Solution: Figure a) shows an imaginary cube of edge L/2. A uniformly…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often mistakenly think the electric flux changes continuously with the rod’s position, even while the entire rod is inside the cube; however, Gauss's law states $\Phi=Q_{\text{enc}}/\varepsilon_0$, so the flux remains constant as long as the amount of charge enclosed does not change.

Figure a) shows an imaginary cube of edge L/2. A uniformly charged rod of length L moves towards the left at a small but constant speed vv. At t = 0, the left end just touches the centre of the face of the cube opposite it. Which of the graphs shown in the figure b) represents the flux of the electric field through the cube as the rod goes through it?

Multiple Choice Options

  • A a
  • B b
  • C c
  • D d

Step-by-Step Verified Solution

**Answer:** Graph c. **Step-by-Step Explanation:** The flux through the cube increases as the rod enters, then remains constant when the rod is fully inside, then decreases as it exits. Graph c represents this.

All Questions in this Chapter

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