Forces Between Current-Carrying Conductors (Cambridge (CIE) A Level Physics): Revision Note

Origin of the forces between current-carrying conductors

• A current-carrying conductor, such as a wire, produces a magnetic field around it

• The direction of the field depends on the direction of the current through the wire

  • This is determined by the right-hand grip rule

• Parallel current-carrying conductors will therefore either attract or repel each other

  • If the currents are in the same direction in both conductors, the magnetic field lines between the conductors cancel out – the conductors will attract each other

  • If the currents are in the opposite direction in both conductors, the magnetic field lines between the conductors push each other apart – the conductors will repel each other

Magnetic field lines around two current-carrying wires

Both wires will attract if their currents are in the same direction and repel if in opposite directions

• When the conductors attract, the direction of the magnetic forces will be towards each other

• When the conductors repel, the direction of the magnetic forces will be away from each other

• The magnitude of each force depend on the amount of current and length of the wire