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Question:

As shown in the figure, two infinitely long, identical wires are bent by 90 and placed in such a way that the segments LP and QM are along the x-axis, while segments PS and QN are parallel to the y-axis. If OP=OQ=4 cm, and the magnitude of the magnetic field at O is 10⁻⁴ T, and the two wires carry equal currents (see figure), the magnitude of the current in each wire and the direction of the magnetic field at O will be (μ₀=4π10⁻⁷ NA⁻²)

20 A, perpendicular out of the page

40 A, perpendicular out of the page

40 A, perpendicular into the page

20 A, perpendicular into the page

Solution:

Magnetic field at 'O' will be due to 'PS' and 'QN' only
i.e B₀ = Bps + Bqn → Both inwards
Let current in each wire = i
∴B₀ = μ₀i/(4πd) + μ₀i/(4πd)
∴i = 20A