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PhysicsNEET 2024Bar magnet and magnetic field lines

Magnetism and Matter

An iron bar of length LL has magnetic moment MM. It is bent at the middle of its length such that the two arms make an angle of 60∘60^\circ with each other. The magnetic moment of this new magnet is:

  1. A.M2\dfrac{M}{2}✓
  2. B.2M2M
  3. C.M3\dfrac{M}{\sqrt{3}}
  4. D.MM

Solution

Bending does not change the pole strength mm; it changes the distance between the poles. The two end poles are now separated by the chord of two arms of length L2\frac{L}{2} at 60∘60^\circ: 2×L2sin⁡30∘=L22 \times \frac{L}{2}\sin 30^\circ = \frac{L}{2}. So M′=m×L2=M2M' = m \times \frac{L}{2} = \frac{M}{2}.

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