What is the force between two long parallel currents that run in the same direction?

What is the force between two long parallel currents that run in the same direction?

• A. They repel.
• B. They attract.
• C. There is no magnetic force between independent wires.
• D. The force is always perpendicular to the currents and independent of direction.

Answer: (B)

Currents in two long parallel wires create magnetic fields that interact. The magnetic field produced by the first wire exerts a force on the current in the second wire. Using the right-hand rule, if the two currents flow in the same direction, the magnetic force on the second wire points toward the first wire, so the wires attract. If the currents flow in opposite directions, the force points away, and the wires repel. The force has a magnitude that grows with the product of the currents and falls off with distance, so there is a definite magnetic interaction between the wires. Therefore, the wires attract when the currents run in the same direction.

Currents in two long parallel wires create magnetic fields that interact. The magnetic field produced by the first wire exerts a force on the current in the second wire. Using the right-hand rule, if the two currents flow in the same direction, the magnetic force on the second wire points toward the first wire, so the wires attract. If the currents flow in opposite directions, the force points away, and the wires repel. The force has a magnitude that grows with the product of the currents and falls off with distance, so there is a definite magnetic interaction between the wires. Therefore, the wires attract when the currents run in the same direction.