A) The magnitude of magnetic moment now diminishes.
B) The magnetic moment does not change.
C) The magnitude of B at (0.0.z), z >>R increases.
D) The magnitude of B at (0.0.z), z >>R is unchanged.
Correct Answer: A
Solution :
| Option [a] is correct. |
| Explanation: For a circular loop of radius R, carrying current J in x-y plane, the magnetic moment M =\[\operatorname{I}\ \times \pi {{\operatorname{R}}_{2}}\]. |
| It acts perpendicular to the loop along z-direction. |
| When half of the current loop is bent in y-z plane, then magnetic moment due to half current loop is x-y plane, \[{{\operatorname{M}}_{2}}=\operatorname{I}(\pi {{R}_{2}}/2)\]acting along z-direction. |
| Magnetic moment due to half current loop in y-z plane, \[{{\operatorname{M}}_{2}}=\operatorname{I}(\pi {{R}_{2}}/2)\]along x-direction. |
| Net magnetic moment due to entire bent current loop, |
| \[{{\operatorname{M}}_{net}}=\sqrt{M_{1}^{2}+M_{2}^{2}}\] |
| = \[\sqrt{2}\frac{\operatorname{I}\pi {{\operatorname{R}}^{2}}}{2}\] |
| = \[\frac{\operatorname{M}}{\sqrt{2}}\] |
| Therefore, \[{{\operatorname{M}}_{net}}\]< M or M diminishes. |
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