The electric whirl comprises of a 3-pointed star wheel with all the points curved in one direction, i.e. rearward.
This set up is pivoted on top of a short insulating shaft.
The base of the stand is provided with a 4 mm connection socket.
Students can appreciate that when the electric whirl is plugged in; a charge builds up on the metallic parts of the whirl, creating a large electric field. Eventually this electric field becomes large enough to ionize the air molecules and creates a space charge that is of the same sign as the points. This mutual repulsion between the space charge and the points, causes the wheel to spin rapidly in a direction that is away from the points.
In fact, even if the electric whirl is given an initial spin in the opposite direction, it will stop and reverse.
- The apparatus has a 95 mm diameter.