Question

Two wires carrying current in opposite directions are placed a distance $a$ apart.
Which of the following will cause the greatest increase in the magnitude of the force between the wires?

• A. Doubling the current in one wire.
• B. Doubling the current in both wires.
• C. Doubling the distance between the wires to $2a$.
• D. Decreasing the distance between the wires to $\frac{a}{2}$
• E. Running the currents in the same direction.

Answer 1

The correct option is B Doubling the current in both wires.

In this case, the force per unit length between the wires is $F=\frac{{\mu }_0{I}_1{I}_2}{2\pi a}$

As force is depends on current in both wires so when we double the current in both wire we get greatest increase of force $F$.

Thus, option B will be correct.