Physics Dept. Demonstration Manual

DEM31.1 - Force on a Current-Carrying Conductor


To show force exerted on a current-carrying conductor in a magnetic field.

  • rolling rod assembly (see figure below)
  • 30A tap switch
  • strong U magnet (as for DEM44)
  • Herniac (Twel power supply)
  • heavy leads


Set up the apparatus as shown above. Set the control knob for DC power to maximum, and turn on the toggle switch.

Pressing the tap switch will cause current to flow through the rod, so that it is repelled by the magnet and rolls up the rack.

When the tap switch is released the rod rolls back down towards the magnet and braking due to eddy currents can be observed.


Do not depress the tap switch for more than a few seconds at a time.