A switching electric field makes a bell ring!
Watch The Video:
Other Demos of Interest:
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Solenoid Train |
Bending Electron Beam w/Magents |
How a Capacitor Works |
Teachable Topics:
- electric fields
- electric charge
- mechanical energy
Theory:
This demo shows the conversion of electrical energy into mechanical energy.
Franklin’s bells were used in the 1700s to ring during lightning storms. A pair of bells was used; one was fixed atop a stake in the ground while the other was connected to a lightning rod. A conductive clapper would be placed between the two bells, and the bell would ring during a lightning storm.
When you touch a plate it becomes grounded. This means the whole plate becomes negatively charged. When you turn on the Van de Graaf generator near the other plate, it becomes positively charged. This also charges the ball, which is repelled from the positively charged plate and swings toward the grounded plate. When the ball hits the grounded plate, it becomes negatively charged. This causes it to be attracted to the opposite, positive plate, so it swings over to it. Once the ball comes into contact with the positive plate, the ball becomes positively charged as well. This causes it to be attracted to the negative plate so it swings across to the other plate. It again becomes negatively charged, so it swings back to the positive plate… and so on.
Apparatus:
- miniature Van de Graaf generator
- two metal plates, unconnected
- small metal ball attached to a string or fishing wire
Procedure:
- suspend the ball between the two metal plates
- touch one plate with your finger to ground it
- hold the Van de Graaf generator near the other plate
- watch as the ball swings between the two plates
