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NEET 2019 Odisha · PhysicsLoop centre fieldPrevious Year Question

A straight conductor carrying current i splits into two parts as shown in the figure. The radius of the circular loop is R. The total magnetic field at the centre P of the loop is:

Answer: (A) Zero. Answer: (A) Solution: The current i splits at the junction into two arcs that meet again at the centre-line, one arc subtending θ₁ = 90° and the other θ₂ = 270°.

NEET 2019 Odisha Physics question — A straight conductor carrying current i splits into two parts as shown in the figure. The…
  1. A.Zero✓
  2. B.3μ₀i/32R, outward
  3. C.3μ₀i/32R, inward
  4. D.μ₀i/2R, inward

Correct Answer

(A) Zero

Solution & Explanation

Answer: (A) Solution: The current i splits at the junction into two arcs that meet again at the centre-line, one arc subtending θ₁ = 90° and the other θ₂ = 270°. The two arcs are in parallel, so the current divides inversely with arc length (∝ resistance): the longer 270° arc carries the smaller current and the shorter 90° arc the larger current, with i₁θ₁ = i₂θ₂. Field of an arc at the centre: B = (μ₀ i_arc θ)/(4πR). Since i₁θ₁ = i₂θ₂, the two arcs produce fields of equal magnitude. The two arcs carry current in opposite rotational senses about P, so their fields are oppositely directed (one into, one out of the page). Net field at P = 0.

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