Getting a charge out of physics

Physics of the Mundane

Adam Johnston

ACharge@ is a fundamental and commonly experienced quantity of nature.  However, understanding it can be a bit elusive.  This lab is meant to be an introduction to creating and studying charge.  There are two different kinds of charge, and depending on what combinations of these charges in the same vicinity, different forces will be felt by each charge. 

Pieces of scotch tape can determine the charge of objects. Your friendly instructor will show you how to “piggyback” pieces of tape in such a manner as to use them for scientific research.  Begin your charge into this topic by playing with the pieces of tape and observing and noting how they interact with one another.

After enough play with the tape, describe the charges of the following, if you happen to know that a balloon rubbed on one=s head (assuming you have hair) or on some fur is generally negatively charged.

C  the “top” and “bottom” pieces of tape

C  a rubber rod (black) rubbed with fur

C  a rubber rod (black) rubbed with wool

C  a glass rod rubbed with silk

Try to come up with some general rules that describe how different charges interact.  You may have to do some careful observation and estimation. Consider the following questions.

? How can you tell that there are different kinds of charge? Why is it important to know the charge of a balloon?

?       How did the rubber rod, glass rod, balloon and scotch tape get their charges? (Where did the charge come from?) How could you test this?

?       It may also be fun to play with an electroscope that your friendly instructor can demonstrate for you.  This also measures charge, but in a slightly more elaborate way.  Describe this device and how it works.