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Electrostatic Induction: Physics Lab

Instructor: Amanda Robb
In this lesson you'll be learning how to conduct an electrostatic induction lab. By the end of the lab you'll have a better understanding of how charges rearrange during electrostatic induction and how this can be applied in physics.

Introduction

Goal: To understand charge rearrangement during electrostatic induction
Age: High school and up
Time to Complete: 1 hour
Safety Concerns: None

Have you ever seen lightening in the sky? This amazing phenomenon might seem mystical, but its actually a product of a process called electrostatic induction. Electrostatic induction is a change in the distribution of charge on an object due to the movement of nearby objects that already have a charge. In the case of lightening, charges build up on the clouds from movement of the air. The difference in charge between the clouds and the ground causes a giant bolt of electricity to connect them, the lightening.

Electrostatic induction does not involve the objects touching, as it does in conduction. Electrostatic induction creates static electricity, where charges build up on an object but do not move. For more information on static electricity, you can read this lesson: What is Static Electricity? - Definition, Causes & Uses.

Today, we're going to measure the affect of electrostatic induction on charge rearrangement of insulators, or objects that don't conduct electricity. To do this we're going to use a tool called an electroscope to measure charge on different objects. When a charged object is near the electroscope's sensor, the electroscope will start to move.

If you need a refresher on what an electroscope is, or if you need to build your own for this lab, check out this experiment first: Electroscope Experiment

Materials

  • Electroscope (easily build your own using the experiment above)
  • Wool
  • Plastic rod
  • Glass rod

Steps

1. Rub the wool on the plastic rod to charge it for about 30 seconds.

2. Next, place the plastic rod near the sensor on the electroscope. Make sure that they do not touch.

3. Observe what happens to the electroscope.

4. Touch the sensor on the electroscope while standing on the ground. The charges will flow through you back to the earth and the electroscope should reset.

5. Repeat step 1-3 with the glass rod.

Troubleshooting

Make sure you rub the wool on the plastic and glass rods for at least 30 seconds. If the electroscope still doesn't move, try rubbing the wool for longer. To get accurate results, make sure your electroscope completely resets before trying the glass rod.

Discussion Questions

Why do you think the electroscope moved?

Which material caused the electroscope to move more? Why do you think that is?

How It Works

During electrostatic induction, charges build up on an object due to the presence of other charged objects near it. The type of charge that accumulates, positive or negative, depends on where the material lies in the triboelectric series, which describes which materials are likely to gain or lose electrons. Wool and glass tend to lose electrons, meaning they become more positive, whereas plastic likes to gain electrons, meaning they become more negative.

The triboelectric series describes what materials tend to gain or lose electrons
triboelectric series

When you rub the wool on the rod, the rod picks up electrons from the wool. This is conduction, since the objects are touching; electrostatic induction comes next. (For more information on conduction you can read this lesson: What is Conduction in Science? - Definition & Examples)

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