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:

A.1 : 4✓
B.1 : 2
C.2 : 1
D.4 : 1

Solution

$M = I A = I π r^{2}$ with the same current, so $\frac{M _{1}}{M _{2}} = \frac{r _{1}^{2}}{r _{2}^{2}} = \frac{1}{4}$ .

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