PURPOSE: To demonstrate Coulomb's law semi-quantitatively.
DESCRIPTION: Two identical conducting balls, one mounted rigidly to a plastic stand, the other suspended from the overhead projector as shown in the picture, are charged with the same charge. As the fixed ball is slid closer to the suspended ball, the angle of the thread support becomes greater, indicating a greater horizontal force. With a little bit of luck, you can actually show that the horizontal force is inversely proportional to the square of the distance between the centers of the two balls.
REFERENCES: (PIRA 5A20.21)
EQUIPMENT: Sphere with bifilar suspension, sphere on lucite block, transparent scale, overhead projector, charging materials (glass with silk and hard rubber with fur).
SETUP TIME: 5 min.
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