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Series Circuit: Sequential Path

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Author: Janice VanCleave

An electrical circuit is the path that electric charges follow. When there is only one path through which an electric current can flow, the circuit is called a series circuit. If any part of a series circuit is broken, then no current can flow through any part of the circuit. Some holiday lights are in series circuits, so when one light burns out the circuit is broken and all the lights stop working.

In this project, you will use a model to demonstrate a series circuit. You will determine how to measure the voltage, current, and resistance of a series circuit. You will also learn how to determine resistance mathematically, using Ohm's law.

Getting Started

Purpose   To demonstrate a series circuit.

Materials

• 1.5-volt battery battery holder with insulated wires (red and black)
• flashlight
• lamp (for E-10 screw-base holder)
• lamp holder with E-10 screw-base

Procedure

1. Place the battery in the battery holder so the battery's negative terminal is at the end with the holder's black wire.
2. Screw the lamp into the lamp holder.
3. Holding the insulated part of the wires attached to the battery holder, touch the bare ends of the wires to the screws on either side of the lamp holder (see Figure 17.1). Caution: Do not leave the wires on the screws for more than a few seconds. The bare wire and lamp can get hot enough to burn you. Allow them to cool before touching them.
4. Observe the lamp when only one wire leading from the negative terminal of the battery touches a screw on the lamp holder.
5. Repeat step 4 using only the wire from the positive terminal.

Results

The lamp glows only when the two wires leading from the battery touch the two screws on the lamp holder, one wire on either side of the lamp holder.

Why?

An electric current is the flow of electric charges. Electric current moves through conductors, such as the connecting wires from the battery holder and the metal parts of the lamp holder, lamp, and battery (a device that uses chemicals to produce an electric current). A path made of conducting materials through which an electric current travels is called an electric circuit. If the electric circuit is a loop, meaning a continuous path, it is called a closed circuit. If there is a separation of the conducting material forming the electric circuit, it is called an open circuit. If the circuit, like the one in this experiment, has only one path through which an electric current can flow, it is a series circuit.

The lamp indicated whether the circuit was open or closed. For the lamp to glow, electrons must move through its filament, which is a thin coil of wire inside the lamp. Because the filament wire is small, the electrons flowing through it are more likely to collide with atoms in the wire. These collisions cause the atoms to vibrate, thus increasing the temperature of the wire. When there is enough current, the wire heats enough to glow. When the circuit was closed, the wires attached to either side of the lamp led to each end of the battery allowing electrons to flow through the circuit, and the lamp glowed. An open circuit was formed when one of the wires from the lamp was removed from the battery. It made a break in the circuit, so the electrons could not flow. The light did not glow when the circuit was open.

The battery provides direct current (DC) (electric current moving in one direction). The arrows indicate that in a closed circuit, the current, indicated by the symbol e' in Figure 17.2, moves away from the negative terminal of the battery, through the lamp, and back to the positive terminal of the battery.

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