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 `xgt0` is now bent so that it now lies in the y-z plane.

Options

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 gt gt R` increases.
D. The magnitude of B at (0.0.z), `z gt gt R` is unchanged.

Answer

A

Explanation

For a circular loop radius R, carrying current I in x - y plane, the magnetic moment `M = I xx pi 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 is x - y plane, `M_(1) = I (pi R_(2)//2)` acting along z direction.
Magnetic moment due to half current loop in y - z plane, `M_(2) = I(pi R_(2)//2)` along x-direction.
Net magnetic moment due to entre bent current loop,
`M_("net") = sqrt(M_(1)^(2) + M_(2)^(2))`
` = sqrt(2) (I piR^(2))/(2)`
`= (M)/(sqrt(2))`
Therefore, `M_("net") lt M` or M diminishes.