Q. A current $i$ is flowing through the loop. The direction of the current and the shape of the loop are as shown in the figure. The magnetic field at the centre of the loop is $\frac{\mu_{0}i}{R}$ times. $(MA = R,\ MB = 2R,\ \angle DMA = 90{^\circ}$

A) $\frac{5}{16},$ but out of the plane of the paper
B) $\frac{5}{16},$ but into the plane of the paper
C) $\frac{7}{16},$ but out of the plane of the paper
D) $\frac{7}{16},$ but into the plane of the paper
Explanation

(d) (i) Magnetic field at the centre due to the curved portion $DA = \frac{\mu_{0}i}{4\pi R}\ \left( \frac{3\pi}{2} \right)$
According to right hand screw rule, the magnetic field will be into the plane of paper.
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(ii) Magnetic field at $M$ due to $AB$ is zero.
(iii) Magnetic field at the centre due to the curved portion $BC$ is $\frac{\mu_{0}i}{4\pi 2R}\ \left( \frac{\pi}{2} \right).$ According to
right hand screw rule, the magnetic field will be into the plane of paper.
(iv) Magnetic field at $M$ due to $DC$ is zero.
Hence, the resultant magnetic field at $M$
$\ \ \ \ = \frac{3\mu_{0}i}{8R} + 0 + \frac{\mu_{0}i}{16R} + 0 = \frac{7\mu_{0}i}{16R}\ $

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.