Electricity and Magnetism -- Resistance

Series circuits

When we connect two circuit elements so that all the current through one of them must then pass through the other, we say they are connected in series. By now, you have lots of experience with series circuits: every circuit we have described so far has been a simple series circuit. We have already referred to "putting batteries in series" (the standard way to connect two batteries in a flashlight). Similarly, we could say that a switch is in series with the circuit elements it controls. In this activity we will study what happens when we put different circuit elements in series.

write in your journal Choose a set of objects to test for their conducting (or nonconducting) ability. Here are some suggestions of interesting materials to try

pencil lead from an automatic pencil (or cut out of a wooden one)
carbon paper
a silvery candy wrapper
water, or very salty or vinegary water, or some of your soda
your fingers (be brave!)

Choose a variety of materials, including some that you are pretty sure is a conductor, some where you are pretty sure that it is not a conductor, and of course some examples where you just don't know at all. Here is a table you can print out to record your observations on these objects.
a circuit with a gap in it

Build this circuit, using two batteries in series, and then fill the gap with one of the objects, to see if it completes the circuit. All the items are in series with each other, because the current is the same everywhere. If the light bulb lights, we will call the object a good conductor. If the light bulb only glows dimly, we will call it a poor conductor. If nothing happens, it is a very poor conductor, or perhaps an insulator. Test each of the objects you have chosen, and enter the results in the table.
Build another circuit by replacing the light bulb by a buzzer, and test the objects again. You will see that some of the objects that gave no response with a light bulb make a tiny sound with the buzzer, while some still do nothing. Enter these results in your table, too.
Finally build a third circuit using a light-emitting diode, and test the objects a third time.

Most objects can be classified as being conductors or insulators; however, this depends somewhat on the sensitivity of the test, since everything conducts a little bit. There also can be nonlinear materials, that do not conduct at all when a small voltage is applied, but become conductors when a larger voltage is applied. The light-emitting diode behaves this way.
write in your journal Record in your journal about what you learned, and any questions or problems you encountered.

Check the box when you are done:
Next:Resistors