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JEE Main & Advanced JEE Main Paper (Held On 12-Jan-2019 Morning)

  • question_answer
    As shown in, the figure, two infinitely long, identical wires are bent by \[90{}^\circ \] 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 C) 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 \[({{\mu }_{0}}=4\pi \times {{10}^{-7}}N{{A}^{-2}})\] [JEE Main Online Paper Held On 12-Jan-2019 Morning]

    A) 20 A, perpendicular into the page 

    B) 40 A, perpendicular into the page 

    C) 20 A, perpendicular out of the page          

    D) 40 A, perpendicular out of the page.         

    Correct Answer: A

    Solution :

    The magnetic field due to wires LP and MQ will be zero at point O. Magnetic field at point O due to the vertical wires is given as \[B={{B}_{1}}+{{B}_{2}}=\frac{{{\mu }_{0}}}{4\pi }\frac{I}{r}(sin0+sin90)+\frac{{{\mu }_{0}}}{4\pi }\frac{I}{r}\]\[(sin0+sin{{90}^{o}})\] \[{{10}^{-4}}=2\times \frac{4\pi \times {{10}^{-7}}}{4\pi }\times \frac{I}{0.04}\Rightarrow I=20A\] By right hand thumb rule direction of magnetic field at O will be perpendicular into the page.


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