Resistance: Series and Parallel Circuits

An electric circuit is a complete path through which charges can flow. Circuits are classified into two basic types: series and parallel. In a series circuit, the charges have only one path to follow, so they must travel through each wire and resistor—an electrical device like a light bulb that resists the flow of electricity. In a string of lights in a series circuit, the more bulbs added to the series circuit, the greater the resistance, or opposition to the flow of electricity, and the dimmer each bulb shines. If one bulb burns out in a series circuit, the other bulbs go out as well because the circuit is broken. A parallel circuit has two or more paths through which charges can flow. If one bulb burns out in the parallel circuit, the charge can still flow along the other path. In this activity you will use drinking straws to demonstrate the difference in resistance along parallel and series circuits.

Materials

Eight drinking straws (thin ones are best); Tape

Activity

1. Create a model of a series circuit by taping four drinking straws together end to end so you have created one long straw. Do not tape over the openings of any of the straws.
2. Create a model of a parallel circuit by evenly placing four drinking straws side by side on the table. Tape the four straws together in this configuration. Do not tape over the openings of any of the straws.
3. Blow through both straw models. Which of the two models was the easier to blow through?

Follow-Up Questions

1. Which of the two models offered less resistance when you attempted to blow through them?
2. Judging from these models, is there more resistance in a series or parallel circuit?

Answers

1. The straws taped side by side.
2. Series.

Extension

Carry out research on schematic diagrams. Draw a schematic of a series circuit with two light bulbs and a battery, and then draw one of a parallel circuit with two light bulbs and a battery.