WHAT DO THE LIGHT BULBS DO?

Transcription

1 Name Date Hour WHAT DO THE LIGHT BULBS DO? Investigation 2: What Can Be Used to Show Charge Flow ate? Part 1 Compass Needle Movement and Bulb Brightness Set-Up Note: The four round bulbs that you re using for this activity should show very nearly the same brightness when connected. If they do not because of different age or manufacture let me know so that we can move bulbs around until everyone has a set of matched bulbs. Four Bulbs Two Bulbs 1. Set up the circuit shown above with four bulbs but do not connect the battery. Place a compass under one wire so that the wire is lined up with the compass needle. Connect the battery and note the amount of movement for the compass needle and the brightness of the bulbs. epeat for the circuit shown above with only two bulbs. Note the amount of movement for the compass needle and the brightness of the bulbs. a. How does the compass needle movement compare for the two circuits? b. How does the bulb brightness compare for the two circuits? 1

2 2. a. Which circuit has a greater charge flow rate? b. How do you know? (What evidence do you have?) 3. How is the brightness of a bulb related to the charge flow rate through the bulb? 4. How is the amount of compass needle movement related to the charge flow rate through the wires? Part 2 Flow ate with and without a Battery Demonstration: 1. Charge the blue capacitor through two round bulbs. Observe very carefully the brightness of the bulbs and the length of time they stay lit. 2. Disconnect the battery from the circuit, and discharge the capacitor again making very careful observations of brightness and lighting time. 3. Are the bulbs brighter during charging or discharging? 4. Based on bulb brightness, when does the circuit have more resistance? 5. Is the lighting time shorter during charging or discharging? 6. Speculate: How do you think lighting time is related to flow rate and why? 7. Does the battery act as if it has resistance inside? What is your evidence? 2

3 8. Speculate: Does charge just flow out at one end of the battery and in at the other end or does it also flow all the way through the battery? Explain your reasoning. 9. If you notice that the bulb in a flashlight has become dimmer than when it was new, what has happened to the flow rate of charge through its filament? a. What has happened to the resistance of the circuit in the flashlight? b. Does this necessarily mean that the resistance of the bulb filament has changed? Part 3 Charge Flow ate in Branches A B A B C No Branches C Branch Added 1. Set up the circuit shown above with no branches and note the brightness of the bulbs and the amount of compass movement under each of the four wires (emember, rotate the circuit to fit on top of the compass). Include a diagram as you record your observations. 2. a. Are all three bulbs equally bright? 3

4 charge flow rate through each bulb? 3. a. Is the amount of compass needle movement the same for each wire? charge flow rate through each wire? 4. Do not disassemble the circuit. Change it into the second circuit with the branch by adding one more round bulb and two more wires. a. What happened to the brightness of bulbs A and C when you added the branch? flow rate through these bulbs? 5. a. Based on the change in brightness of bulbs A and C, what has the charge flow rate from battery done, increased or decreased? b. As far as the battery is concerned, has the circuit become a more difficult place or an easier place for the charge to move through? 6. a. What happened to the brightness of bulb B when you added the branch? charge flow rate through the middle two bulbs? 4

5 7. Check the compass needle movement under one of the wires connected to the battery and under one of the branch wires. (Diagram your circuit and note where you took your measurements.) a. How do they compare? b. Does this agree or disagree with the bulb brightness? 8. a. What do you think is happening to the charge flow as it enters the branch part of the circuit? b. Is charge being used up or lost in the branches, or does it continue to flow back to the battery? c. What is your evidence? 5