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Lecture Demonstrations Laboratory


The Demonstrations Manual


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Electrostatics
Electric Fields And Potential
Van de Graaff Generator
Electrostatic Bell
Electric Lines of Force
Electrostatic Motor
Electric Fields
Gauss' Law
Radio in Faraday's Cage
Lightning Rod
Electric Wind
Ionic Drive
Smoke Precipitator
Capacitance
Current and Resistance
Electromotive Force And Current
DC Circuits
Magnetic Materials
Magnetism
Inductance
Induction
Complex Circuits
Semiconductors And Tubes
Transmission Lines and Antennas

Gauss' Law

Purpose:

To show that excess charge resides totally on the outside of an insulated conductor.

Procedure:

Charge the metal cylinder by touching it with the Teflon rod (charged with fur or silk) a few times. Show that there is a charge on the cylinder by bringing it close to the electroscope. Then lower the ball into the hole in the cylinder making sure not to touch the edges. Extract the ball with the same care after banging it around inside the cylinder. Touch it to the electroscope and note the absence of charge. Now touch the outside of the cylinder with the ball and demonstrate with the electroscope that the ball is charged.

Hints:

Be patient and careful. Ground the cage before the first trial, ground the ball on the rod between the sets, be mindful of not touching the edges of the cylinder while extracting the stick from inside.

In case of wet weather one can use the following trick: charge the cup with a Wimhurst machine (lots of charge that doesn't leak off very fast) and instead of electroscope use a pith ball. When the charge is taken from inside the cup the ball will stay immobile while when taken on the outside the ball will deviate.

Comments:

If you have a suggestion for the use of this demo which might benefit others, you can enter it below.

Equipment:

  • Silk
  • Ball on the rod
  • Metal Cylinder on Stand
  • Electroscope
  • Teflon Tod
  • Cat's fur