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4.2.2 – Parallel Circuits NAME: 1 DATE: PARTNERS: Purpose: To study the properties of a basic parallel circuit. Materials: 1. 2. 3. 4. 5. 2 bulbs, and bulb holders 1 AA battery 8 alligator clips 1 Ammeter (0‐1 A) 1 Voltmeter (0‐3 V) Diagram: Light bulbs in battery holders Procedure: 1. Connect a simple series circuit with ONE bulb, and one battery. Measure the current with the ammeter (in series) of this basic series circuit: 4.2.2 – Parallel Circuits 2 2. PREDICT: If you add a 2nd bulb in parallel, as shown in the diagram above, will both bulbs be equally bright, or will there be a difference in brightness? Explain. What will happen to the brightness of the first bulb? Also, will the current in the two branches differ, or be the same? 3. DISCUSS: Talk with your group about your prediction. Are there any different predictions in your group? If so, write them down, with the explanation behind each one. When your group reaches a consensus, move on to the next step. 4. OBSERVE: Connect the second bulb to the circuit as shown in the diagram. Record your observations about the brightness of the bulbs. Were your predictions correct? 4.2.2 – Parallel Circuits 5. (c) (a) 1 2 (b) This parallel circuit can be thought of as two current loops (1 and 2), as indicated in the above diagram. Measure the current in the following places. Note: to measure current properly, the ammeter must be connected in series. Current in loop 2, between the two bulbs – noted by ammeter position (a): Current in loop 1 – noted by ammeter position (b): Total current in the circuit ‐ noted by ammeter position (c): 6. a) Compare the currents in loops 1 and 2 with each other. What is the relationship here? b) Compare the currents in each loop with the total current in the circuit. What is the relationship here? 3 4.2.2 – Parallel Circuits c) Compare the total current in parallel with two bulbs, with the total current for two bulbs in series, with one battery. (May need to refer back to Series Circuit activity.) Explain your findings. Questions: 1. Remove one of the bulbs. What happens to the brightness of the other one? Why? 2. Measure the voltage across each bulb in the parallel circuit using the voltmeter (both bulbs screwed in) Bulb 1: (V) Bulb 2: (V) Compare the voltages across each bulb, and compare these voltages with the voltage of the battery: 4 4.2.2 – Parallel Circuits Now, measure the voltage across one of the bulbs when the other one is unscrewed from its holder: Is the voltage across a bulb changed when an identical bulb is placed in parallel with it? Explain how this is different from a series circuit. 3. Are the outlets in your home arranged in parallel or series? Why are they designed this way? 4. If you were to design your own chandelier for your dining room, would you want the bulbs to be in series, or parallel? Explain why. 5 4.2.2 – Parallel Circuits 6 5. As a review, sketch how you would wire a 3‐bulb circuit as a series circuit, and a parallel circuit. Resources: Cunningham, James and Norman Herr. Hands‐On Physics Activities With Real‐Life Applications, (West Nyack: The Center for Applied Research in Education, 1994), p. 581 4.2.2 – Parallel Circuits 7 Summary and Suggestions for the Future: (Please attach extra pages as necessary to fully answer these questions) 1. What were the important concepts of physics/science that you learned from this activity? What else did you learn? 2. Can you think of alternative hands‐on ways in which these concepts could be demonstrated? Can you suggest any improvements to these activities? 3. What changes would you make to teach these activities in a Grade 7‐8 classroom? What difficulties can you foresee?