Make An Electroscope

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My daughter is working her way through Apologia’s Physical Science during her 9th grade year of homeschool. She loves Apologia for the readable style and the hands-on activities and experiments. Students really get to “do” science!

Atoms are usually electrically neutral with an equal amount of protons (positively charged particles) and electrons (negatively charged particles). Sometimes, an atom loses an electron and that electrical balance is thrown off. The atom then has a positive charge. If an atom gains an electron, that atom would be negatively charged.

Check out this intro to atoms post.

How can we tell if an object contains electrically charged atoms? We can make our own detecting device called an electroscope.

Testing Electric Charge With An Electroscope

Supplies

• a clear glass or jar
• a plastic lid to fit over the glass or jar
• a paper clip
• two small strips of aluminium foil
• an inflated balloon
• pliers
• tape

Procedure

Straighten the paper clip with pliers or your hands. Bend the straightened wire into a shape with a center loop with two hooks beneath it.

Cut a slit into the plastic lid so that the hoops from the wire stick through but the center loop sits on top of the lid. Tape the wire into position.

Poke a hole into one end of the aluminum foil strips and hang them on the wire hooks.

Place the lid with the wire and aluminium foil strips onto the glass.Take the inflated balloon and rub it on your hair to charge the balloon with negatively charged electrons. Slowly bring the balloon close to the wire loop. Don’t touch the wire. Watch the foil strips.

As the balloon gets close to the wire, the foil strips should start to move.  If they do not, your balloon may not be charged enough. Rub it onto your hair more vigorously.

Next, move the balloon away from the wire and then slowly move it closer to the wire again. This time, touch the wire with the balloon. Watch the foil strips. What happened?

What Happened?

When you rubbed the balloon on your hair, the balloon picked up electrons from the hair and the balloon became negatively charged. This is called static electricity. As you moved the balloon close to the wire on the electroscope, it “detected” the negative charge.

The foil and the wire on the electroscope had a neutral charge at the beginning of the experiment. When the balloon approached the electroscope, the negative charge of the balloon repelled the negatively charged electrons in the paper clip and the foil. When those electrons reached the ends of the two strips of foil, they became negatively charged and repelled each other. This is what caused the foil to move.

When the balloon was moved away, the charge returned to neutral and the strips moved back to where they were at the beginning of the experiment.

Did you touch the balloon to the wire? If you did, the balloon would have transferred its extra electrons to the electroscope. This would have caused the foil strips to stay repelled from each other even when the balloon was removed. To make the charge of the electroscope neutral again, just touch the wire with your finger. The extra electrons would then move into your body. When the charge of the electroscope is neutral, the foil strips will return to their starting position.

Use your electroscope to detect charges in other objects around the house. Try creating static electricity with combs, rubbing vinyl records with  your hands, or dragging your feet across carpet.

To learn more, use the Physical Science curriculum from Apologia Science!