Electrostatic pendulum setup

A hollow aluminum sphere is suspended near a working Van-De-Graaff generator (see top picture). The sphere oscillates back and forth due to induction.

Explanation:

Because the dome of the Van De Graaff generator is negatively charged, the electric field created by the dome causes the redistribution of charges on the aluminum sphere’s surface. Positive charges on the sphere’s surface move to face the dome, while negative charges move away to the opposite side.

When the instructor removes the negative charges by using the discharging rod (see top picture), the sphere is left with a net positive charge. This causes the sphere to be attracted by the dome, gradually leaning towards the generator until a spark occurs between the two. Without touching the Van De Graaf generator, the spark discharges the dome, causing the sphere to be negatively charged and repelled. The induction process redistributes the sphere’s charges again, and the sphere begins oscillating (see video).

Notes:

• This demonstration requires the use of video camera when shown to a large audience.