Question

Two long current carrying conductors are placed parallel to each other at a distance of 8 cm between them. The magnitude of magnetic field produced at mid-point between the two conductors due to current flowing in them is 30 μT. The equal current flowing in the two conductors is:

• A. 30 A in the same direction
• B. 30 A in the opposite direction
• C. 60 A in the opposite direction
• D. 300 A in the opposite direction

Answer 1

Answer: (B)

30 A in the opposite direction

Answer 2

The correct answer is (B) : 30 A in the opposite direction
If currents are equal in both wires and field at mid-point is not zero, then the current is in opposite direction to sum up the fields at the point.

Fig.

As B net ≠ 0 that is the wires are carrying current in opposite direction.
$\frac{μ_0l × 2}{2π (4×10^{-2})} = 30 × 10^{-6} T$
$⇒ I = \frac{30 × 10^{-6}}{10^{-6}} A = 30 A$
in opposite direction.