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PRACTICE / Field of a current loop

Zero here does not mean zero everywhere

Two concentric loops have radii 0.10 m and 0.20 m. The inner carries 2 A with magnetic moment along +z. Choose the opposing outer current so that the field at their common centre is zero.

What is the resulting signed total magnetic moment along z?

Organize the givens & assumptions
  • Inner radius 0.10 m, current 2 A
  • Outer radius 0.20 m, opposing current adjusted for centre cancellation

Thin circular coaxial loops in vacuum; currents steady; use vector superposition. The question asks for magnetic moment, not centre field.

  1. A00
  2. B−0.14π A m2-0.14\pi\ \mathrm{A\,m^2}
  3. C+0.14π A m2+0.14\pi\ \mathrm{A\,m^2}
  4. D−0.06π A m2-0.06\pi\ \mathrm{A\,m^2}

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