======Franklin’s Bells======


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**Alternative titles:** Electrostatic Bells
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====Summary====                   
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====Procedure====  
  - Suspend a small metal ball on a string so that it hangs freely between two unconnected metal plates.  
  - Ground one plate by touching it with your finger.  
  - Rub a plastic rod (e.g., PVC or acrylic) with wool or fur to give it a static charge.  
  - Bring the charged rod near one of the plates so that it charges up by induction.  
  - The ball is attracted to the charged plate, touches it, and becomes charged.  
  - Once charged, the ball is repelled and swings toward the grounded plate.  
  - After contact, the ball picks up the opposite charge and is pulled back toward the charged plate.  
  - The ball continues to swing back and forth, transferring charge between the plates.



====Links==== 
DEMO: Franklin's Bell - Professor Hafner: 
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Franklin's Bell - How it Works - RimstarOrg: 
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====Variations====
  * Try using different materials (PVC, acrylic, hard rubber) for the rod and compare effectiveness.  
  * Use two differently charged rods to test how opposite charges affect the behavior.  
  * Perform the demo in a darkened room to see small sparks at contact points.



====Safety Precautions====
  * Do not let students touch the plates while the rod is charged.  
  * Ensure the suspended ball is securely attached so it does not fly off.  
  * Keep the charged rod away from sensitive electronics, as static discharges can cause damage.




====Questions to Consider====
  * How does the plastic rod charge the plate without touching it? (By induction, it repels or attracts electrons in the plate.)  
  * Why does the ball keep moving back and forth instead of stopping after one swing? (It alternately picks up charge from each plate, causing continual attraction and repulsion.)  
  * How does this version compare to using a Van de Graaff generator? (The principle is the same, but the charge from a rod is weaker and may not sustain oscillations as long.)  
  * What natural phenomenon was Franklin trying to detect with his lightning bells? (The presence of atmospheric electricity during thunderstorms.)