Verified Solution • 2025–26 Session moderate

QJEEM19Ph2e71: JEE Main 2019 Physics - Class 12 JEEM19Ph2e71 Solution: As shown in the figure, two infinitely long, identical wires…

As shown in the figure, two infinitely long, identical wires are bent by 90o 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 = 4cm, 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 ( μ\mu 0 = 4 π\pi ×\times 10–7 NA–2) :

JEE Main 2019 (Online) 12th January Morning Slot Physics - Magnetic Effect of Current Question 159 English

Multiple Choice Options

  • A 40 A, perpendicular into the page
  • B 40 A, perpendicular out of the page
  • C 20 A, perpendicular into the page
  • D 40 A, perpendicular out of the page

Step-by-Step Verified Solution

Magnetic field at 'O' will be done to 'PS' and 'QN' Only

i.e. B0 = BPS + BQN →\to Both inwards

Let current in each wire = i

∴\therefore   B0 = μ0i4πd+μ0i4πd{{{\mu _0}i} \over {4\pi d}} + {{{\mu _0}i} \over {4\pi d}}

or      10 −- 4 = μ0i2πd{{{\mu _0}i} \over {2\pi d}} = 2×10−7×i4×10−2{{2 \times {{10}^{ - 7}} \times i} \over {4 \times {{10}^{ - 2}}}}

∴\therefore        i = 20 A

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