Franklin’s Bells With Van de Graaff Generator

A small conductive ball swings back and forth between two metal plates, alternately charging and discharging as it contacts each plate.

1. Suspend a small metal ball on a string so that it hangs freely between two unconnected metal plates.
2. Ground one plate by touching it with your finger.
3. Bring a Van de Graaff generator near the other plate to charge it positively.
4. Observe as the ball is repelled from the positive plate and swings to strike the grounded plate.
5. After contact, the ball becomes negatively charged and is attracted back toward the positive plate.
6. The ball continues to shuttle between the two plates, ringing like Franklin’s original lightning bells.

Van de Graaff 1 - Franklin's Bells - Robert Bass:

Franklin bell experiment with Van De Graaff generator - jcableman:

📄 Franklin's Bells - Classroom Physics Demos: https://demos.smu.ca/index.php/demos/e-n-m/171-franklin-s-bells

• Use different sizes of spheres or plates to see how mass and surface area affect oscillations.
• Demonstrate in a dark room to look for sparks during contact.

• Do not touch the Van de Graaff generator or charged plate during operation.
• Keep sensitive electronics away from the setup to avoid electrostatic discharge damage.
• Ensure the suspended ball is securely attached so it cannot fly free.

• Why does the ball continue to swing between the plates once started? (It is alternately charged positive and negative by contact with each plate, leading to attraction and repulsion.)
• What kind of energy conversion does this demonstrate? (Electrical energy is converted into mechanical motion.)
• How did Franklin use bells like this in the 1700s? (He connected them to lightning rods so they would ring during thunderstorms, signaling atmospheric electricity.)
• What modern devices use a similar principle of electric charging and discharging? (Electrostatic precipitators, capacitors, and some sensors.)