5H15.10 Magnetic Field of a Solenoid Current


Magnetic field from a solenoid current


Current through a solenoid deflects compass needles or arranges iron filings, showing the field lines around the wire.



  • [1] Mounted copper solenoid
  • [1] Power supply with leads
  • [3] Compass
  • [1] Shaker of iron filings
  • [1] White paper sheet
  • [1] Power bar
  • [1] Document camera or overhead projector

Classroom Assembly

  1. Place wire and compasses, if desired, under document camera or on projector. If using document camera, place sheet of paper underneath for visibility.
  2. Place power supply nearby, plugged into a power bar that is plugged into mains power.
  3. Attach power supply leads to wire.

Important Notes

  • Do not turn on for longer than necessary since the current carrying conductor becomes hot over time and the power button on the power supply can weld open.
  • The button on the power supply can get stuck. If it does, you can turn off the power supply by turning off the power bar.
  • The contacts are critical. If the demo is not working properly, loosen the contacts on the power supply and retighten.
  • The Plexiglas platform will not focus on all overhead projectors. Ensure the demo will work on your classroom overhead projector in advance.
  • Compass polarities can be reversed. Bring spare compasses. Undamped compasses work best for this demo.



  1. Observe undeflected compass direction.
  2. Press button to activate current. Observe deflected compass needles.
  3. Release button to stop current.
  4. Turn off power bar.
Iron filings:
  1. Hold down button to activate current.
  2. Sprinkle iron filings around the wire.
  3. Release button to stop current.
  4. Turn off power bar.
  5. Dump iron filings onto paper sheet and put them back into the shaker.


Additional Resources


  • PIRA 5H15.10


  • Don't attempt this at home!

Last revised

  • 2018


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.