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7. Move Away

Purpose To demonstrate that electrons move.

Materials aluminum foil, as thin as possible glass jar, 1 qt. (1 liter) soft plastic lid to cover top of jar large paper clip needle-nosed pliers modeling clay

scissors

balloon, 9 in. (23 cm) pencil

scissors

adult helper

Procedure

Cut two strips of aluminum foil 1/2 in. x 2 in. (1 cm x 5 cm).

Use the point of the pencil to make a small hole in the top of each foil strip.

Ask an adult to use the pliers to reshape the paper clip into a loop at the top and two hooks on the bottom (see diagram).

Use the pencil to make a hole in the center of the plastic lid.

Push the loop of the wire through the hole in the plastic lid and mold a small piece of clay around the base of the loop to hold it in place.

Hang the foil strips on the wire's hooks.

Place the lid on top of the jar.

Inflate the balloon and rub it on your hair. Your hair must be clean, dry, and oil-free.

Hold the balloon near the loop, on top of the jar.

Results The metal leaves move apart when the charged balloon is held near the metal loop.

Why? The instrument made is called an electroscope, or charge detector. The metal strips move when the loop is placed in an electrically charged area. Electrons are rubbed off of your hair and onto the balloon, charging the surface of the balloon with a negative charge. Holding the negatively charged balloon near the metal loop causes the negative electrons on the surface of the metal to move away from the balloon because like charges repel, that is, move away from each other. Electrons move down the metal wire and build up on the aluminum strips. Since like charges repel each other, the two negatively charged strips move apart.

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