Two long parallel wires carry currents in the same direction. What is the direction of the magnetic force between them?

Two long parallel wires carry currents in the same direction. What is the direction of the magnetic force between them?

• A. They rotate around each other
• B. They attract
• C. They repel
• D. They exert no force

Answer: (B)

When currents flow in the same direction in two long parallel wires, they attract each other. The reason is that each wire creates a magnetic field around it. At the position of the second wire, this magnetic field interacts with the current in that wire, causing a force along the line toward the first wire (the force is given by F = I L × B). This results in an attractive pull between the wires. If the currents went in opposite directions, the force would reverse and they would repel. The idea that they would rotate around each other isn’t how the straight-line forces between parallel wires work, and there would be no force only if there were no current or no magnetic field.

When currents flow in the same direction in two long parallel wires, they attract each other. The reason is that each wire creates a magnetic field around it. At the position of the second wire, this magnetic field interacts with the current in that wire, causing a force along the line toward the first wire (the force is given by F = I L × B). This results in an attractive pull between the wires. If the currents went in opposite directions, the force would reverse and they would repel. The idea that they would rotate around each other isn’t how the straight-line forces between parallel wires work, and there would be no force only if there were no current or no magnetic field.