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Through which bulb is the current higher under these operating conditions? Or is current the same in each? Justify ii

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Through which bulb is the current higher under these operating conditions? Or is current the same in each? Justify ii. Which bulb do you think has the higher voltage dropped across it under these operating conditions? Or is the voltage across each the same? Justify. Keep your explanation in mind as you explore this circuit more fully in the next section c) The equivalent resistance of a series combination Intro: Each bulb's filament acts as an obstacle to the flow of charge and develops a potential drop across it. You can also consider the two bulbs in series as a single obstacle. There is a current in "it" and a potential difference across "it," so "it" has a resistance. In this section, you will explore how the resistance of this series combination compares with the resistances of each bulb, and hopefully shed light on the mystery encountered above. Procedure: With the two bulbs in series, determine the resistance of each bulb. Remember, since the resistance of a bulb depends on the current in it, you cannot use the measurements you made in the previous section, to find the resistances. Rather, you must make new measurements under these different operating conditions. In the box below draw three separate circuit diagrams for the three different measurements you must make to determine each bulb's resistance while connected in series and powered by the supply set at 5V. Use only the following symbols as needed. Use the stylus to select a region

de Voltage Incandescent Wire Current Meter Voltage Meter Supply Lamp for ammeter) (or voltmeter) Conduct the measurements and record the results with appropriate units in Table 2 below, and then calculate the resistance of each bulb under these operating conditions. Bulb Measure Bulb Measured Bulb Calculated Bulb Current Voltage Resistance (Show Work) #1 #2 Table 2 Conclusion: Pause here, since you now have the evidence, to check your earlier predictions. i. Which bulb has the higher resistance under these operating conditions (#1 or #2)? Or do they have the same resistance? Were you correct? (yes or no) ii. Through which bulb is the current higher under these operating conditions (#1 or #2)? Or is current the same in each? Were you correct? (yes or no)

iii. Which bulb has the higher voltage dropped across it under these operating conditions ((#1 or #2)? Or is the voltage across each the same? Were you correct? (yes or no) Procedure Cont. What current and what voltage do you need to measure to experimentally determine the combined resistance of the two bulbs in series? In the box below describe the two measurements that need to be made and draw a circuit diagram for each. Carry out the measurements, record the results in Table 3 below, and calculate from your data the combined equivalent resistance of the two bulbs in series. Measured Measured Calculated Combined Current Voltage Resistor (show work) Table 3 Conclusion: Compare the resistance of the series combination to the resistance of any one of the two bulbs; namely, is it smaller, equal to, or larger than either single bulb resistance? Do your results suggest a mathematical relationship between the individual resistances and the combined resistance? If so, what?

Ill. Parallel Connection Intro: In this part of the lab you will explore parallel combinations of bulbs. The behavior of a parallel combination is different than a series combination. It is important that you develop a good understanding of both. In Part a you will explore a parallel combination of identical bulbs. In part b you will look at a parallel combination of bulbs that are not identical. a. Parallel circuit with identical elements in each branch Prediction: Imagine the two circuits shown in Figure 2. All three bulbs are the same type. Bulb C in the circuit on the right is said to be "in parallel" with the bulb B, and you say that each bulb sits in a different branch of the circuit. Figure 2: Single Bulb and Parallel Bulb Circuit Now, make a prediction. What will be the order of brightness of the three bulbs, A, B, and C? In other words, which will be brightest, second brightest, and least bright. You may also say that you think two or more bulbs will have the same brightness. Write down your prediction and a supporting reason. Procedure: Build the circuits following the same procedures in the previous part, and see. A good way to compare brightness, almost simultaneously, is to build only the circuit on the right and watch the brightness of B as you quickly connect and disconnect C. When C is disconnected bulb B behaves as bulb A would - That is the length of the light ray emitted in each case. Record the order of brightness. Any surprises?

Conclusion: What can you conclude about the current in each of the parallel bulbs in comparison with the current in the single bulb? (Be careful with this question. Let your observations tell you the answer, not your preconceptions.) Prediction: Now that you have observed the circuit in operation, check your thinking about current in the circuit. The circuit in Figure 3 below is exactly the same parallel combination, but the wires have been redrawn in a slightly different way. Let's say the current in wire segments B-G and H-E is i,. These are the wires in the branch containing bulb #1, so this is also the current through bulb #1. Relative to i,, predict the currents in the other four wire segments. Put your answers in the boxes. (For example, if you think the current is 10 times greater, pencil in 10i,.) Figure 3: Parallel Bulbs - Prediction Procedure: To test your prediction rewire the circuit exactly as shown in Figure 3. You'll have to use more wires. Note how three connect together at point B and another three at point E. Connect wires together such that they make "y" shaped junctions to create these "meeting points". Make sure both bulbs light, equally bright, as a check of your wiring. Measure the actual currents in the various branches of the circuit, and write down the results, with units, in the boxes shown in Figure 4 below. (Note that you will have to think carefully about making this measurement. To measure the current in wire AB you have to replace the wire with the ammeter. The same is true for the wire BC and the others.

In addition to these current measurement, measure the potential drop across the output terminals of the power supply, the potential difference across bulb #1 and the potential difference across bulb #2. How do they compare? Check your thinking: In a circuit similar to the one above, the current through two identical bulbs in parallel is 3 A. The current delivered by the supply is 6 A. In other words, they split the total, halfand-half. If a third identical bulb is connected in parallel with the other two, creating a third branch, what will the current be through each bulb? Give a numerical answer. For the same circuit, say the supply voltage is 6 V. What resistance do the three parallel bulbs combined present to the battery? (This is the equivalent resistance of the combination, which can be calculated here as the battery voltage divided by the current delivered by the battery.) b. Parallel circuit with different elements in each branch Intro: In the parallel circuit you just studied, each branch of the circuit contained an identical #1 bulb. Both bulbs were equally bright, had the same current, and the sum of their currents equaled the total supply current. In this section, you will explore what happens when one of the branches is changed in some way so that it is different from the other branch. How does the change in one branch affect the other branch? Prediction: Consider the previous circuit shown in Figure 3; both bulbs are similar. Predict what would happen to the current through bulb #1 if you were to remove bulb #2 from the circuit. Explain. Procedure: Try it. Disconnect bulb #2 from the circuit. What do you see? Does what you see agree with your prediction? With bulb #2 still disconnected measure the current through bulb #1. Record your result here.

Predict what would happen to the current through bulb #1 if you were to wire a different type of bulb in parallel with #1. Explain. Procedure: While measuring the current through bulb #1 connect the second in parallel with it. Measure the current through bulb #2 and record the result. Also measure the current drawn from the positive terminal of the power supply. Record your result. Analysis: Are the currents in the two branches, one containing bulb #1 the other bulb #2 equal? Is their sum equal to the current from the supply? Conclusion: Summarize what you have learned about parallel circuits with two branches by answering these three questions. i) Describe how the currents in the branches of a parallel circuit compare to the total current. ii) Describe how the current in one branch depends on the current in the other branch. iii) Use the stylus to select a region h each other

c. The equivalent resistance of a parallel combination Intro: Each bulb acts as an obstacle to the flow of charge and develops a potential drop across it. You can also consider the two bulbs in parallel as a single obstacle. There is a current through "it" and a potential drop across "it," so "it" has a resistance. In this section you will explore how the resistance of this parallel combination compares with the resistances of each bulb. Prediction: Determine the resistance of both light bulbs while operating in parallel. You have made all the necessary current and voltage measurements previously. Compile your results in Table 4 below. Then calculate the resistance of each bulb. If you are unsure about any measurement, repeat it. Measure Bulb Measured Bulb Calculated Bulb Bulb Current Voltage Resistance (Show Work) #1 #2 Table 4 What current and what voltage do you need to measure to experimentally determine the combined resistance of the two bulbs in parallel? Describe the two measurements that need to be made. Draw a circuit diagram if you think that would help your explanation. If you have made them previously record your results immediately in Table 5 below; if not, make the measurements first and then calculate the combined resistance. Measured Current Calculated Combined Measured Voltage Resistance (Show Work) Table 5 Conclusion: Compare of each bulb ind bulb res ista Use the stylus to select a region

- How does the measured equivalent resistance compare to the result obtained from the formula for combining parallel resistances, Req = (R. + R. ? Show your work.