5B10.30-Franklin’s bell

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Description: A conductive ball is suspended between two vertical parallel plates connected to the Wimshurst machine.
The ball strikes one plate and obtains that charge; it is then repelled by that plate and is attracted to the other plate.
The ball strikes the other plate, is discharged and obtains the charge of the plate it just struck, thus being repelled again.
This sequence soon becomes very rapid and the ball begins to bounce from one plate to the other, sounding like a bell.

Equipment:

  • Wimshurst machine
  • Parallel plate capacitor
  • Jack stand
  • Metal ball on string and rod
  • Stand and clamps
  • Two banana plug and clip wires

Setup:

  1. Test the Wimshurst machine to make sure it is operating properly
    • ALWAYS discharge the machine by connecting the two balls with the Y-bar tool, making sure not to touch any of the metal parts, whenever you touch the machine and after you finish spinning it
    • Bring the two balls on the machine close, but not touching, and turn the crank. The wheels should start spinning in opposite directions, and a spark should jump between the two balls
    • If the wheels are not spinning, check to make sure the bands are attached properly, and that one is twisted such that the wheels will spin in opposite directions when the crank is turned
    • If there are no sparks generated, make sure the steel wool comes in contact with the metal strips on the wheels, and make sure the balls are close enough
  2. Move the two balls far from one another, and clip one wire to one of the balls, and plug it into the non-insulated plate
  3. Attach a second wire to a ground (the metal wheel of a cart works well) and plug it into the insulated plate
  4. Hang the ball between the two plates, towards the top of each plate, but in the middle of the separation, using the stands and the clamps

Demonstration:

  1. Spin the Wimshurst machine; the ball should start moving and hitting the plates
  2. When finished, remember to discharge the machine with the Y-bar

Notes:

  • Take care when handling the Wimshurst machine; the machine can produce high voltages, which could be dangerous
  • ALWAYS discharge the machine before and after you use it
  • The ball may need a small push to get moving, and the ball may continue moving between the plates if you’ve spun the machine enough and haven’t discharged it
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