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Published: 10 November 2020

• electromagnetism
• simulation

The Van de Graaff Generator was featured recently with a new animation of its inner workings. This week, we’re taking a look at the physics behind one of the most popular demonstrations that use it: demonstration J1-26, the levitating pie pans.

In this new video featuring Landry Horimbere, we can see the demonstration in action!

As the belt moves inside the Van de Graaff generator, it deposits an imbalance of charge on the combs inside the dome. These charges accumulate on the outside of the dome. When the conductive plates are placed on top of the dome, they accumulate the same charge.

Because like charges repel each other, the pie plates gradually try to push apart. When there is enough charge built up on the top plate to have a repulsive force greater than the force of gravity pulling it down, it lifts off and flies away.

In these animations by Don Lynch, you can see how the generator builds up charge…

and how the charges distribute through the pans to create the repulsion effect.

Also, the National High Magnetic Field Laboratory has shared this tutorial on Van de Graaffs: https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/van-de-graaff-generator, another fun way to explore this electrifying demonstration!