A heavy vertical conductor in a power station passes downwards through a horizontal steel support plate. A direct current passes downwards through the conductor as shown.

Draw on this

On the diagram, sketch the magnetic field caused by the current in the conductor.

In the same facility, two long, flexible parallel horizontal power cables are suspended close to each other.

• When direct currents pass in opposite directions through the two cables, they are observed to push apart (repel).
• If the current in one of the cables is reversed, they are observed to pull together (attract).

Explain why the cables experience these forces and why reversing one current changes the direction of the force.