Two long parallel conducting wires, each carrying equal current \( I \) in the same direction, are placed at a distance of \( 2r \) between them. The magnetic field at mid-point \( P \), between them is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Zero
The field of a long straight wire at distance r is \( \mu_0 I/2\pi r \), with its direction given by the right-hand rule. Point P is at distance r from each wire:
\( \displaystyle B_1 = B_2 = \frac{\mu_0 I}{2\pi r} \)
With both currents upward, the field of the left wire at P (to its right) points into the page, and the field of the right wire at P (to its left) points out of the page. The two fields are equal and opposite, so the net field at the mid-point is zero.