Electroscope Experiment

Instructor: Amanda Robb
In this physics lab you'll be designing an electroscope to detect electric charge. By doing this experiment you'll be able to explain how the principles of induction, conduction, and grounding apply to the electroscope.

Introduction

Goal: To create an electroscope to detect electric charge
Age: Middle school and up
Safety concerns: Get an adult to help you punch a hole in the lid. Scissors or an awl can be sharp.
Time: 1 hour

Have you ever rubbed a balloon on your hair? You might remember your hair standing straight on end, almost seeking out the balloon. Why does this happen? A scientific principle called static electricity, or the buildup of charges is responsible. If you'd like a refresher on static electricity, you can watch this video lesson: What is Static Electricity? - Definition, Causes & Uses.

When you rub the balloon on your hair your hair transfers electrons, or negatively charged particles, to the balloon. Now your hair has a positive charge, causing it to be attracted to the negative charges on the balloon. How else could we tell if an object has a charge? One way is through a device called an electroscope, which we'll be making today.

Materials

  • Glass jar with lid
  • Awl
  • 2'' of plastic straw
  • 10'' of 14 gauge copper wire
  • Hot glue
  • Pliers
  • Balloon
  • Any other materials you'd like to test for a charge, such as carpet, rubber, or vinyl
  • 2 - 2'' square pieces of aluminum foil (or gold leaf)

Steps

Safety Tip!! Get an adult to help you punch a hole in the lid.

1. Start by punching a hole in the jar lid large enough for the straw and copper wire to fit through.

2. Insert the straw into the hole and center it. Leave a couple inches of space from the bottom of the jar. Use the hot glue to secure the straw in place.

3. Next, insert the copper wire into the straw, with about 2'' protruding from the straw inside the jar.

4. Use the pliers to bend 1'' of the copper wire into a hook to hold the aluminum foil later.

5. Use the pliers to bend the remaining copper on top of the lid into a coil to provide more surface area.

6. Next, cut a small slit in the aluminum foil and slide them onto the copper hook.

7. Attach the lid to the jar.

Electroscope setup
setup

8. Now, rub the balloon on your hair.

9. Place the balloon next to the copper coils. Observe what happens to the metal inside the jar.

10. Move the material away and touch your hand to the coiled wire. Observe what happens.

11. Repeat step 8-10 with any other materials you would like to test.

Troubleshooting

Make sure you use the correct gauge wire. Thicker wire will conduct more electricity, thus producing a stronger result. Thinner wire, or fewer coils will not work as well. For the best results, make sure you thoroughly rub the balloon or other materials on your hair. They must accumulate a sufficient charge for the electroscope to detect it.

Discussion Questions

What happened when you put the charged material near the electroscope and why?

What happened when you touched the electroscope?

Why did we use aluminum foil or gold leaf inside the jar and not plastic?

How It Works

An electroscope detects electrical charge. When you rubbed the material on your hair, your hair transferred electrons to the material, giving it a negative charge. This process is called induction, or the process of accumulating charge.

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