Understanding Franklin's Wheel: A Van de Graaff Experiment

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SUMMARY

The discussion centers on Franklin's Wheel, an experiment involving a Van de Graaff generator. The sharp points of the wheel create an intense local electric field that ionizes nearby air, resulting in the formation of ions. These ions are expelled due to the electric field, generating an "electric wind" that propels the wheel in a specific direction. The direction of rotation, whether clockwise or counterclockwise, is determined by the orientation of the sharp points on the wheel.

PREREQUISITES
  • Understanding of electric fields and their effects on charged particles.
  • Familiarity with ionization processes in gases.
  • Basic knowledge of Van de Graaff generators and their operation.
  • Concept of electric wind and its applications in electrostatics.
NEXT STEPS
  • Research the principles of electric fields and their role in ionization.
  • Explore the mechanics of Van de Graaff generators and their experiments.
  • Learn about the concept of electric wind and its practical applications.
  • Investigate the factors influencing the direction of rotation in electrostatic devices.
USEFUL FOR

Students and educators in physics, electrical engineers, and hobbyists interested in electrostatics and experimental physics will benefit from this discussion.

amirali75
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Hey guys,
I'm new to this forum so I'm sorry if I posted in the wrong thread. So we did these experiments with van de graaff and I almost understood all of them except what seems to be "Franklin's wheel" experiment. I know for one thing that the air near the sharp points are ionized but I don't get why it actually turns and also why counterclockwise?
Any help is appreciated.
 
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The sharp points create an intense local electric field which induces a charge on nearby atoms of air (oxygen, nitrogen etc.) by 'sucking' all the opposite charges away. The charged atoms (now called ions) are repelled by the field and shoot away like the exhaust of a jet engine. (This is called electric wind)
The reaction of that jet is what drives the wheel around.

Which way it turns depends on which way you have the points.
 

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