Verified Solution • 2025–26 Session moderate

QPages 140-141: Q6: HC Verma: Concepts of Physics - Volume 2 Gauss's Law Pages 140-141: Q6 Solution: In the following figure shows a charge q placed at the centre…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often think that because Gauss’s law gives the net flux through a closed surface, any charge outside a hemisphere cannot affect the flux through its curved surface. In fact, Gauss’s law applies only to closed surfaces; an open surface can receive flux from external charges. Here, only charges placed on the symmetry axis (A or C) produce field lines that are perpendicular to the surface normals everywhere, giving zero net flux. Always check the symmetry of the external charge relative to the surface normal before assuming the flux is unchanged.

In the following figure shows a charge q placed at the centre of a hemisphere. A second charge Q is placed at one of the positions A, B, C and D. In which position s) of this second charge, the flux of the electric field through the hemisphere remains unchanged?

Multiple Choice Options

  • A A
  • B B
  • C C
  • D D

Step-by-Step Verified Solution

**Answer:** (a), (c). **Step-by-Step Explanation:** Charges at A and C (on the axis of the hemisphere) do not change the flux through the hemisphere. Charges at B and D do change the flux.

All Questions in this Chapter

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