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A current loop, having two circular arcs joined by two radial lines is shown in the figure. It carries a current of 10 A. The magnetic field at point O will be close to

Asked in JEE Main 9th Jan 1st Shift 2019 · Arcs and combined shapes

Figure: Arcs and combined shapes
Answer: (1) 1.0×10⁻⁵ T

Step-by-step solution

Radial lines point at O, so they give no field.

Arcs: θ=45°=π/4, radii r₁=3 cm and r₂=5 cm, currents in opposite senses.

B=(μ₀ Iθ)/(4π)(1/(r₁)-1/(r₂))=10⁻⁶×π/4×(1/(0.03)-1/(0.05))

B≈1.05×10⁻⁵ T

Why the other options are wrong

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