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PhysicsNEET 2025Torque on a current loop, moving-coil galvanometer

Moving Charges and Magnetism

A 2 A current is flowing through two different small circular copper coils having a radii ratio of 1 : 2. The ratio of their respective magnetic moments will be:

  1. A.1 : 4✓
  2. B.1 : 2
  3. C.2 : 1
  4. D.4 : 1

Solution

M=IA=Iπr2M = IA = I\pi r^2 with the same current, so M1M2=r12r22=14\frac{M_1}{M_2} = \frac{r_1^2}{r_2^2} = \frac{1}{4}.

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