BCIT Physics Department

Demonstration Manual

Electricity and Magnetism

DEM40 - Generator


- To study both alternating and direct currents produced by a generator.


The above apparatus and schematic are used for both DEM40 and DEM41.


The hand-driven generator employs an electromagnet to produce the necessary magnetic field. The brushes are interchangeable from DC (commutator) to AC (slip rings). On DC the OHP shows a unidirectional current with magnitude and direction being a function of armature velocity and direction of rotation. On AC armature rotation produces a bipolar, sinusoidal current, occupying both halves of the center-zero ammeter.


  1. Turn the armature slowly to observe the effects since mechanical inertia within the ammeter movement plus the effects of damping can mask observations.

  2. The DPDT knife switch must be returned to the "center-off" position to avoid overheating the field coil.

  3. Demonstrations DEM40 and DEM41 are very conveniently presented together as one package, with selection made via the knife switch.