
(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.
[image:4_image122.emf]
(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}\ $