Magnetic field around a wire carrying current:

$\overline{){\mathbf{B}}{\mathbf{=}}\frac{{\mathbf{\mu}}_{\mathbf{0}}\mathbf{i}}{\mathbf{2}\mathbf{\pi}\mathbf{r}}}$

Right-hand rule: Thumb points in the direction of current, fingers curl in the direction of the current.

Applying the right-hand rule to wires carrying current in opposite directions, the magnetic field between them is directed in the same direction.

Two long wires are parallel and carry current in opposite directions. The currents are 8.0 and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:

A. 0

B. 4.0 × 10^{–4}

C. 8.0 × 10^{–4}

D. 12 × 10^{–4}

E. 20 × 10^{–4}

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