Question

If two infinitely long wires carry currents in the same direction, then the field at a point P which is lying midway between them is :

• A. twice the field due to each of the wires
• B. half of the field due to each wire alone
• C. square of the field due to each wire alone
• D. zero

Answer 1

The correct option is D zero

Magnetic field due to a current carrying wire is given by, $B=\frac{{\mu }_{0}I}{2\pi r}$
and for direction, point the thumb along the direction of current then curl the fingers around will represents the direction of the magnetic field.
In case of two infinitely long wires carrying currents in the same direction, the field due to both of them at a point P which is lying midway between them will cancel each other and their resultant will be zero.