Question

A current carrying circular loop of radius R is placed in the x-y plane with centre at the origin. Half of the loop with x > 0 is now bent so that it now lies in the y - z plane.

• A. The magnitude of magnetic moment now diminishes.
• B. The magnetic moment does not change.
• C. The magnitude of at (0.0.z), z >> R increases
• D. The magnitude of at (0.0.z) z >> R is unchanged

Answer 1

Answer: (A)

The magnitude of magnetic moment now diminishes.

Answer 2

For a circular loop of radius R carrying current I placed in x-y plane the magnetic moment $\mathrm { M } = \mathrm { I } \times \pi \mathrm { R } ^ { 2 }$it acts perpendicular to the loop i.e. along z-direction when half of the current loop is bent in y-z plane, then magnetic moment due to half current loop in x-y plane $\mathrm { M } _ { 1 } = \mathrm { I } \left( \pi \mathrm { R } ^ { 2 } / 2 \right)$ acting along z-direction.

Magnetic moment due to half current loop in y-z plane $M _ { 2 } = I \left( \pi R ^ { 2 } / 2 \right)$ along x-direction

Effective magnetic moment due to entire bent current loop,

$= \frac { \mathrm { I } \pi \mathrm { R } ^ { 2 } } { 2 } \sqrt { 2 } < \mathrm { M }$

i.e. magnetic moment diminishes