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Question: Answered & Verified by Expert
A steady current flow in a long wire. It is bent into a circular loop of one turn and the magnetic field at the centre of the coil is B. If the same wire is bent into a circular loop of n turns, the magnetic field at the centre of the coil is
PhysicsMagnetic Effects of CurrentJEE Main
Options:
  • A Bn
  • B nB
  • C nB2
  • D n2B
Solution:
1138 Upvotes Verified Answer
The correct answer is: n2B
The magnetic field a circular coil (for n number of loops)

B=μ0ni2r

When, n1=1, n2=2

2πr1=n×2πr2

r1r2=n1

So B1B2=μ0n1i2r1μ0n2i2r2

BB2=n1n2.r1r2

BB2=1n.1n

B2=n2B

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