CIE A Level Physics (9702) 2019-2021

Revision Notes

25.4.2 Forces Between Current-Carrying Conductors

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 thumb 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
  • 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

Worked example

Origin_of_the_Forces_Between_Current-Carrying_Conductors_Worked_example_-_Forces_on_Parallel_Conductor_Question, downloadable AS & A Level Physics revision notes

Origin_of_the_Forces_Between_Current-Carrying_Conductors_Worked_example_-_Forces_on_Parallel_Conductor_Answer, downloadable AS & A Level Physics revision notes

      • Newton’s Third Law states:
        • When two bodies interact, the force on one body is equal but opposite in direction to the force on the other body
      • Therefore, the forces on the wires act in equal but opposite directions

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