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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.
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