A current loop of area $A$ carrying current $I$ has a MAGNETIC MOMENT of magnitude
A$IA$
B$I/A$
C$I^2 A$
D$\sqrt{IA}$
Answer & Solution
Correct answer: A. $IA$
1. syllabus defines the magnetic moment as $\vec{m} = I\,\vec{A}$.
2. The vector $\vec{A}$ has magnitude equal to the LOOP AREA, and direction along the loop's normal (right-hand rule).
3. For multi-turn coils with $N$ turns: $\vec{m} = N\,I\,\vec{A}$.
4. Units of magnetic moment: $\text{A\,m}^2$, the SI unit for magnetic dipole moment.
5. The magnetic moment is analogous to the ELECTRIC dipole moment $\vec{p}$: torque in a field, energy in a field, far-field behaviour all parallel between the two.
6. Options B, C, D have wrong dimensions or wrong dependencies.
_Source: syllabus Physics Part 1, Ch 4, §4.10 (Magnetic Moment of a Current Loop, Eq. 4.30), p. 21–22._
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