Franklin Bells

Van de Graaff generators produce high voltages (50-400 kV) capable of delivering painful shocks. While current is typically low and not life-threatening, shocks can cause involuntary muscle contractions and startle responses. Do not touch the generator dome, connecting wires, or central bell while operating. Keep students at least 1 meter away from the apparatus. Individuals with pacemakers or other electronic medical devices should maintain greater distance (3+ meters) as a precaution.

Always discharge the Van de Graaff generator using a grounded discharge wand or sphere before touching any part of the apparatus. Approach slowly to avoid large sparks. The Franklin bells will stop ringing abruptly when discharged—this provides a useful teaching moment about stored charge.

Purpose

Demonstrates electrostatic induction, charge transfer, and energy conversion (electrical to mechanical to sound). Small conducting spheres shuttle charge between a charged central bell and grounded outer bells, ringing continuously as long as the Van de Graaff operates.

Franklin bells apparatus on a wooden base: central glass column with brass fitting and radiating brass arms, six polished dome-shaped bells in three pairs, with small metal clappers suspended on threads between the central column and each outer bell

Franklin bells connected via red wire from the top of the central column to the dome of a large Van de Graaff generator on a blue base with power switch

Figure 1: The Franklin bells apparatus. The central column connects to a high-voltage source; the outer bells are grounded through the brass frame. Small metal clappers swing between them to transfer charge.

Figure 2: Complete setup: the Franklin bells connected by a red wire to the Van de Graaff generator dome. The generator's blue base houses the motor and belt.

Danger: High Voltage Electrical Hazard

Warning: Discharge Procedure

Purpose

Safety Warnings

Danger: High Voltage Electrical Hazard

Warning: Discharge Procedure

Purpose