Tutorial details

The tutorial leads students through a process of model building by making observations, introducing assumptions to account for their observations, and then testing and modifying the assumptions as needed. Students begin by exploring how to make a light bulb glow using only a battery and a single wire. They discover that it is necessary to form a complete path that connects both terminals of the battery and different parts of the bulb. Students then carefully examine a bulb to specify how a bulb should be connected to form a circuit. The idea that an electric current flows through a complete circuit is introduced and emphasized.

In sections II and III, students make observations of circuits containing two bulbs. Using the assumption that the brightness of a bulb indicates the amount of current through that bulb, students make inferences about the relative current through bulbs in series and parallel circuits

In particular, students recognize that adding a bulb in series to a circuit increases the resistance of the entire circuit and thus decreases the current through the battery, while adding a bulb in parallel decreases the resistance of the circuit and increases the current through the battery. In the last section of the tutorial, students investigate a slightly more complicated circuit that cannot be analyzed completely using a current model. This result motivates the voltage model for current, which is covered in the subsequent tutorial.

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This tutorial assumes no prior knowledge of electric circuits, current, or resistance.

Equipment

List

• battery
• battery holders (2)
• D-cell
• white board or large sheet of paper with markers
• bulbs (large with glass broken so student can see how inside wires are connected)
• bulbs (#14) in sockets
• ample connecting wire including some alligator clips

Discussion