SM214     Barlow’s Wheel     circa 1965     Electricity and Magnetism

  The action of an electric current in a magnetic field is clearly illustrated by Barlow’s Wheel.   This consists of a light, toothed metal wheel that can rotate about a horizontal axis and is arranged so that one or more teeth can dip into a small mercury trough thus providing a continuous electrical contact while the wheel is moving.   A horseshoe magnet is placed with its poles on either side of the mercury trough.

  When an electric current is passed in from the pivot of the wheel and through the mercury contact with the teeth, the wheel turns due to the action of the fixed field on the field due to the electrical current.   The direction of rotation depends on the direction of the current and the polarity of the magnetic field.