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QPage 276: Q13: HC Verma: Concepts of Physics - Volume 2 Permanent Magnets Page 276: Q13 Solution: A very long bar magnet is placed with its north pole coinciding …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often incorrectly assume that because the magnetic field is perpendicular to the current element, the net force must be non-zero; however, the force on each segment is radially outward, and by symmetry, these radial components cancel completely, resulting in a net force of zero.

A very long bar magnet is placed with its north pole coinciding with the centre of a circular loop carrying as electric current i. The magnetic field due to the magnet at a point on the periphery of the wire is B. The radius of the loop is a. The force on the wire is

Multiple Choice Options

  • A very nearly 2πaiB2\pi aiB perpendicular to the plane of the wire
  • B 2πaiB2\pi aiB in the plane of the wire
  • C πaiB\pi aiB along the magnet
  • D zero

Step-by-Step Verified Solution

**Answer:** (d) zero. **Step-by-Step Explanation:** The magnetic field due to the magnet at the periphery is along the axis (perpendicular to the wire). The force on the wire is F = i dl _ B. Since dl is perpendicular to B, the force is radial. By symmetry, the net force on the loop is zero.

All Questions in this Chapter

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