Conductors and dielectrics: Testing Experiment

Aim

To test a model of the internal structure of metal and plastic objects which will allow you to predict the outcome of the experiment

Prior Knowledge

1. Electric charge and electric force.

Description of the Experiment

This experiment has two parts. In the first part the charged electrode of a Wimshurst generator is brought near a soda can on the left side. A light styrofoam disc covered with aluminum foil hangs on the other side (on the right side) of the can, touching it. Use the model of the internal structure of metals to predict what will happen to the light disc covered with aluminium as the ball of the generator gets charged and then brought close to the left side of the can. Make sure that you predict what happens to the disc before the ball touches the can and then right after it touches. In the second part, experiment is repeated with a plastic bottle. Predict the outcome of each experiment before watching the video. To help, draw a picture representing the behavior of charges inside the metal can and the plastic bottle.

Addtional Information

Note that the two metal balls of the Wimshurst generator used in this experiment have opposite charges.

Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.

Questions

1. Why did the aluminum disk start moving away from the can even before the charged ball of the generator touched it?
2. Why did the aluminium disk fly away from the soda can after the ball touched the can? How do you know?
3. What do you need to assume about the internal structure of the soda can in order to explain this?
4. If the aluminium disk became charged, what charge did it receive:
   • The same as the ball of the Wimshurst generator which was brought close to the can
   • The opposite charge?
   What part of the video helps you answer this question?
5. What can you say about the internal composition of the can that explains both parts of the experiment: before the ball touched it and after it did.
6. Why do you think nothing happened to the disk when the experiment was repeated with a plastic bottle? What do you need to assume about the internal structure of the bottle?
7. Why do we call metals electric conductors and plastic materials electric insulators?