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EXPERIMENT 2: A Series Circuit

THINGS YOU NEED: Homemade switch (from Experiment 1). Four 1½-volt penlight bulbs. Four small sockets. 6-volt lantern battery. Some insulated wire.


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.

Latimerís later work focused on parallel circuits. To see why, letís build a series circuit:

Youíll need a switch, four l½-volt penlight bulbs, a few pieces of wire, and a 6-volt battery. Connect the wires as shown in the diagram.

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, if someone wanted to read the newspaper or watch television, he 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 if one light bulb burnt out ó all the other bulbs would go out too.