Two long straight wires are set parallel to each other. Each carries a current i in the same direction and separation between them is 2 r. The intensity of magnetic field midway between them is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → zero
A long straight wire produces a field \( B = \mu_0 i/2\pi r \) at distance r, with its direction given by the right-hand thumb rule. Midway between the wires each is at distance r, so the two fields have equal magnitude.
\( \displaystyle B_1 = B_2 = \frac{\mu_0 i}{2\pi r} \)
For currents in the same direction, the fields at a point between the wires point in opposite directions, so they cancel.
\( \displaystyle B = B_1 - B_2 = 0 \)