LECTURE DEMONSTRATION MANUAL | Instructional Research Lab : ucla physics
Simple Electrostatics Experiments

E.l.l Simple Electrostatic Experiments

Cold, dry days are best for these demos.

a. A rubber rod is charged negative by rubbing it with rabbit's fur. A lucite rod is charged positive by rubbing it with silk. When one charged rubber rod is placed in a stirrup, another charged rubber rod will repel it, but a charged Lucite rod will attract it. This simple but graphic demonstration shows that charges come in two sorts.
b. The charged rods will pick up bits of paper and styrofoam by polarization.
c. The charged rods will first attract hanging pith balls by polarization. When the balls touch the rod, they acquire some of its charge and thereafter are repelled from the rod strongly. The pith balls now hang apart, repelling each other.
d. If a charged rod is brought near an electroscope, its leaves will diverge. If the rod is touched to the electroscope, the leaves will remain diverged, even when the rod is moved away. The electroscope can be charged by induction by grounding it with your finger when the charged rod is near. Remove your finger and then the rod, and the electroscope is now charged with the opposite charge of the rod. This can be checked by bringing the charged rod near again; the leaves now come together.

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