5H40.10 Lorentz Force Between Parallel Wires


Lorentz force, magnetic fields from current, Ampère's law


When currents in wires run parallel, the wires attract due to the magnetic fields from the currents and the Lorentz force. The currents can also be run anti-parallel, making the wires repel.



  • [1] Parallel wires in holder
  • [3] Banana cable
  • [1] Xantrex HPD 15-20 DC Power Supply
  • [1] Document camera or overhead projector

Classroom Assembly

  1. Place the holder under document camera or on overhead projector.
  2. Use the Scotch-Brite to rub off oxides from the ends of the wires.
  3. Connect the wires and hook up banana cables in desired configuration: parallel or anti-parallel. Use the wider spacing of wires for parallel currents and the closer spacing for anti-parallel currents.
  4. Turn current knob to 0 and voltage knob to maximum.

Important Notes

  • The copper wires become hot over time. Make sure to turn off the current when done!
  • All wires should be scrubbed with Scotch Brite prior to use to remove corrosion.
  • The mounting plates for the wires can move a bit, so make sure they don't touch each other.


  1. Turn on the current supply and slowly increase the current until the wires move.
  2. Turn off the current and change wire configurations.
  3. Turn on the current and slowly increase the current until the wires move.
  4. Turn off the current.


Additional Resources


  • PIRA 5H40.10


  • Don't attempt this at home!

Last revised

  • 2020


  • Original construction: two 16.5" lengths of 20 gauge wire were bent into a ‘swing’ shape (a square U with arms on each end). Four Plexiglas legs were attached to a 5" x 8.5" Plexiglas plate to form a raised platform. Four banana plug contacts were threaded through the Plexiglas platform and were each attached to a .5" x 1" copper plates. One or two holes were drilled in the plates so the copper ‘swings’ could be either 0.5 cm or 2.5 cm apart.
  • To remove oxides from hard-to-reach corners of the wires, scrape using a razor blade.

Related AV

Related demos

  • Magnetic field of a wire current


If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.