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Question: Answered & Verified by Expert
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
(MA=R, MB=2R, DMA=90°)

PhysicsMagnetic Effects of CurrentJEE Main
Options:
  • A 516μoiR, but out of the plane of the paper
  • B 5 16 μ 0 i R , but into the plane of the paper
  • C 716μoiR, but out of the plane of the paper
  • D 716μoiR, but into the plane of the paper
Solution:
2870 Upvotes Verified Answer
The correct answer is: 716μoiR, but into the plane of the paper

(i) The magnetic field at the centre due to the curved portion DA=μ0i4πR 3π2

According to the right-hand screw rule, the magnetic field will be into the plane of the paper.



(ii) The magnetic field at M due to AB is zero.

(iii) The magnetic field at the centre due to the curved portion BC is μ0i4π2R π2.

According to the right-hand screw rule, the magnetic field will be into the plane of the paper.

(iv) The magnetic field at M due to DC is zero.

Hence, the resultant magnetic field at M

BM=Bsmall loop+Bbig loop 

Both are perpendicular downward

BM=μOi4πR32π+μOi4π2Rπ2 

BM=716μOiR  

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