Van de Graaff and Soap Bubbles

Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff

Categories: Van de Graaff Generator

Alternative titles: Charged Bubbles Demonstration

Summary

Soap bubbles blown toward a Van de Graaff generator are first attracted by induction, then repelled after they acquire charge.

Procedure

Set up a Van de Graaff generator in a space where bubbles can drift freely.
Use a soap bubble gun (or simply blow bubbles) so that they fall from above toward the charged dome.
Observe: bubbles are initially attracted and move closer to the generator.
When one bubble touches and pops on the dome, droplets become charged and spread to other bubbles, charging them.
The remaining bubbles are now repelled by the generator and begin moving away.
Record the experiment on video, play back in slow motion, and ask students to refine their observations and explanations.

Links

Van de Graaff generator and bubbles - Science experiment - Coolphysicsvideos Physics:

Static Electricity and Bubbles! - Jefferson Lab:

📄 Does Van de Graaff not like a shower? - Wouter Spaan: https://interactivetextbooks.tudelft.nl/showthephysics/demos/demo10/demo10.html

Variations

Slow the video to highlight the moment bubbles switch from attraction to repulsion.
Try adding light paper pieces along with bubbles for comparison (paper is only attracted, not repelled).
Replace bubbles with mist or smoke to show differences in behavior.

Safety Precautions

Do not touch the Van de Graaff generator while it is running.
Keep liquids (bubble solution) away from electrical equipment.
Ensure the generator is properly grounded when turned off.

Questions to Consider

Why are bubbles first attracted to the generator but later repelled? (They are neutral at first and attracted by induction; later they acquire charge from droplets of popped bubbles, leading to repulsion.)
What role does induction play in the initial attraction? (Water molecules in the bubble wall align with the electric field, causing a net force toward the charged sphere.)
Why do some bubbles move away from each other? (They carry like charges and repel one another.)
How is this demonstration an example of scientific inquiry? (Students form hypotheses, make predictions, observe carefully, and test which explanation best fits the evidence.)