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A Series Circuit

Ages:  10 and up
Materials: Homemade switch (from Experiment 1). Four 1 1/2-volt penlight bulbs. Four small sockets. 6-volt lantern battery. Some insulated wire.
Time Required: 2 hours

A series circuit looks like a loop. The same electric current flows through all of the parts of the circuit, sort of like a toy train running around a single-closed track.

Nearly 100 years ago, during the early days of electric lighting, a few experimenters proposed that house lights be wired using series circuits. For a while, Lewis Latimer was an assistant to one of these men. The idea worked ... but not very well. Latimer's later work focused on parallel circuits. To see why, let's build a series circuit:

You'll need a switch, four 1 1/2-volt penlight bulbs, a few pieces of wire and a 6-volt battery. Connect the wires as shown in the diagram.

Switch with Battery and Several Penlight Bulbs

When you turn the switch on, the four bulbs light up together; when you turn the switch off, the four bulbs go out together. It is impossible to control the bulbs individually. This is one reason that series circuits are not practical for use in home lighting: it is not possible to control the lights in different rooms throughout the house on the same circuit. For example, someone who wanted to read the newspaper or watch television would have to turn on a switch that would put on every light and electrical appliance in the whole house.

To discover another reason, unscrew one of the lit bulbs. All the other bulbs go out since the series circuit is broken. Imagine what would happen in a series-wired house in one light bulb burned out — all the other bulbs would go out too.

Remember to play it safe around electricity. Use caution and wear safety glasses and other appropriate dress when building and performing experiments.