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- [JEE Main 12-Jan-2019 Morning]

\[({{\mu }_{0}}=4\pi \times {{10}^{-7}}N{{A}^{-2}})\]

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 :

[a] 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

By right hand thumb rule direction of magnetic field at O will be perpendicular into the page.