I don’t think there is an explanation for why like charges repel. They just do. The world would be totally different if they don’t.
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Here is an worked example on the calculation of the resultant electric force.
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Unfortunately, many electrostatic demonstrations are difficult to pull off in Singapore because of the humidity. But you can watch them in the following video.
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The ultimate demonstration of “like charges repel and unlike charges attract”: combining the tinsels that came with the fun-fly sticks with the good old fashioned van der Graff generator. Notice also that both “charge by induction” and “charge by conduction” are demonstrated.
Applets:–
This applet illustrates why a charged balloon sticks to walls.
PhET Balloon and Static Electricity: Click HERE
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This quirky applet illustrates how we get static shocks.
PhET John Travolta: Click HERE
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Supplementary Reading
It’s All Electric: Click HERE
xmPhysics 