Predict and Explain Task - Adding a Resistor in Parallel

Activity Description

This activity uses the Circuit Construction Kit from the PhET website. Students are shown a circuit with two 10 ohm light bulbs connected in series with a 9 V battery. The circuit will be broken and a third light bulb will be added in series. The students are asked to predict the effect of adding the third light bulb in series on the current reading and the brightness of the light bulbs. The question is resolved by breaking the circuit in the simulation and adding the light bulb.

Target Conceptual Difficulty

Adding resistors in series decreases current in contrast to a common student conception that adding more resistors in will always increase demand for current.

PowerPoint

Predict and Explain Task - Adding a Resistor in Series (Turning Point)

Predict and Explain Task - Adding a Resistor in Series (iClicker)

Simulation

http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

Click on the link Play with Sims. Then in the left frame Click on the link Electricity, Magnets, and Circuits, then click on the icon for Circuit Construction Kit. Once the simulation starts, click on load and then browse to and run the following file. PET Add a Resistor in Series

Presentation Notes

To demonstrate the correct answer to the students, break the circuit, then click and drag another light bulb and connect it at the gap in the circuit.

Student Results

Students predictions were about evenly split between the reading on the ammeter decreasing (47%) and remaining the same (43%) with a few who felt it would increase (10%). Looking at the reasoning it was evenly split between the correct reasoning of increased resistance and the fact that the battery hadn't changed. The battery idea is consistent with research that suggests students think of batteries as constant current sources.

When asked to predict the effect on the brightness of the light bulbs, 71% of the students initially correctly answered that it would decrease. This seemed like an ideal opportunity to use peer instruction, but after the students discusses the question among themselves, only 19% gave the correct answer and 71% shifted to the answer of the brightness remaining the same, consistent with the battery being a source of constant current.

Pen and Paper Actvivities

Pen and Paper version of this activty

Follow up tipers from homework assignments, test reviews and test items

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Last Updated: August 21, 2009