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QPages 338-339: Q2: HC Verma: Concepts of Physics - Volume 2 Electromagnetic Waves Pages 338-339: Q2 Solution: A compass needle is placed in the gap of a parallel plate…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume a steady magnetic field exists between the capacitor plates once a DC battery is connected, forgetting that the magnetic field is produced only by the changing electric field (displacement current) during the brief charging transient. After the capacitor is fully charged, the displacement current ceases and the needle returns to its original position.

A compass needle is placed in the gap of a parallel plate capacitor. The capacitor is connected to a battery through a resistance. The compass needle

Multiple Choice Options

  • A does not deflect
  • B deflects for a very short time and then comes back to the original position
  • C deflects and remains deflected as long as the battery is connected
  • D deflects and gradually comes to the original position in a time that is large compared to the time constant

Step-by-Step Verified Solution

**Answer:** (b) deflects for a very short time and then comes back to the original position. **Step-by-Step Explanation:** During charging, displacement current creates a magnetic field that deflects the needle. After charging is complete, the field disappears, and the needle returns.

All Questions in this Chapter

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