| Physical Science - FME [Phys 101] Spring 2004 |
[1] Set up the two-bulb circuit depicted below.
In this arrangement, we say that the two bulbs are in series.
How does the brightness of your two bulbs compare? What does this imply about the amount of current flowing through each of them?
How does the brightness of each of these bulbs compare with the situation in which there was only one bulb in the circuit? What does this imply about the current flowing through two bulbs in series as compared to the current flowing through a single bulb?
[2] Agree or disagree with the following three statements, and use your results above to support your position.
(i) "Electrical current is used up as it goes through light bulbs."
(ii) "When items are placed in series in a circuit, their order determines how much current each one gets."
(iii) "By observing the circuit above, one can determine that electrical current flows out of the positive side of the battery and back into the negative side."
[3] Now consider this two-bulb circuit, but don't hook it up yet.
In this arrangement, we say that the bulbs are in parallel.
Predict the behavior of the bulbs by adopting one of the following positions:
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The bulb on the left will be brighter. |
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The bulb on the right will be brighter. |
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The two bulbs will have the same brightness. |
Predict also how the parallel bulbs will compare with the earlier circuits:
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The bulb on the left in the parallel circuit will be (brighter than/dimmer than/the same brightness as) the bulb in the single-bulb circuit, and will be (brighter than/dimmer than/the same brightness as) the bulbs in the series circuit. |
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The bulb on the right in the parallel circuit will be (brighter than/dimmer than/the same brightness as) the bulb in the single-bulb circuit, and will be (brighter than/dimmer than/the same brightness as) the bulbs in the series circuit. |
[4] Ok….hook up the parallel circuit and check your results.
[5] Were you correct? If any of your predictions disagree with your experimental results, explain what was wrong with your reasoning.
[6] Use what you have learned so far to predict the relative brightness of each bulb in the following circuit:
[7] Hook the circuit up and test your predictions. Again, comment on any discrepancies between your predictions and experimental observations.
[8] Are any of the bulbs in the above circuit in series? If so, name them.
[9] Are any of the bulbs in the above circuit in parallel? If so, name them.
[10] More Predictions:
When Bulb A is unscrewed, Bulb B will __________ and Bulb C will ___________.
When Bulb B is unscrewed, Bulb A will __________ and Bulb C will ___________.
When Bulb C is unscrewed, Bulb A will __________ and Bulb B will ___________.
After choosing, check your predictions.
[11] As a group, answer the following question.
Suppose you have a closed box in a circuit, as shown. You observe a certain brightness in Bulb A. Imagine that someone makes a change in the electrical elements inside the box. You do not see what has been done, but you do observe that Bulb A becomes brighter.
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What can you conclude about the current flowing through the battery? |
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What can you conclude about the total resistance in the circuit? Has it increased, decreased, or remained the same? Explain. |
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As Homework for Monday, April 12, 2004, complete the following problems:
[1] Two students are having a dispute about a circuit containing only one battery and one bulb. The first says, "When the bulb is lit, there is a flow of current from the battery to the bulb. There is also an equal flow from the bulb back to the battery". The second one replies, "The flow of current is only from the battery to the bulb. We know this is so because a battery can light a bulb, but a bulb can't do anything without a battery".
With which student do you agree, if either? Explain.
[2] Another dispute results in the following two positions:
Student 1: "Adding bulbs to a circuit increases the total resistance. There is a bigger obstacle to the current, so less flows."
Student 2: "Adding bulbs to a circuit may increase or decreases the total resistance. It all depends on how you add them. If you add them in parallel, you give the current more pathways, so the total resistance is less."
Again, decide whether you agree with either student. Explain your position.
[3] Consider the circuits on the next page.
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Rank all of the bulbs (A-H) in order of brightness. If two or more bulbs have the same brightness, be sure to say this. |
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Rank the bulbs by the amount of current flowing through them. |
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Rank the circuits by the amount of current flowing through the battery. |
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Rank the circuits by the total resistance that each bulb arrangement provides to the flow of current. |