Pre-LAB 4 Assignment Fundamentals of Circuits II: Currents ...

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Fundamentals of Circuits II: Currents & Circuits v 0.3 to the current in a circuit as opposed to something that uses up current. If each bulb provides its own resistance, how is the total resistance of a circuit is affected by the addition of bulbs as in Fig. 1(b)? Question 1.10 Create a qualitative rule which can be used to predict whether current increases or decreases as the total resistance of a circuit is increased. Real-Time Physics Comment: “The rule you have formulated based on your observations with bulbs may be qualitatively correct–correctly predicting an increase or decrease in current– but it won’t be quantitatively correct. That is, it won’t allow you to predict the exact sizes of the currents correctly. This is because the resistance of a bulb to current changes as the current through the bulb changes. Another common circuit element is a resistor. A resistor has a constant resistance to current regardless of how large the current through it. In the next activity you will reformulate your rule using resistors.” Prediction 1.4 Fig. 4 shows circuit diagrams where the light bulbs of Fig. 1 have been replaced by identical resistors. Consider the amount of current going through each resistor in Figures 4(a) and 4(b)? Rank the currents through each resistor resistors A, B and C. Explain your reasoning. (You may consider these resistors as ideal resistors: an ideal resistor has a constant resistance independent of the current passing through it.) To test your predictions, in addition to the equipment you have been using, you will need • Two 10-ohm resistors Activity 1.3: Current in a simple circuit with resistors Step 1: Continue to use the experiment file L2A1-2 (Two Currents ). Step 2: Zero the probes with them disconnected from the circuit. Step 3: Connect circuit shown in Fig. 5(a). Step 4: Withthecurrentprobes, usetheanalysisfeatureinthesoftwaretomeasurethecurrent through resistor A in circuit 5(a) and the currents through resistors B and C in circuit 5(b). PHYS-204:Physics II Laboratory 8
Fundamentals of Circuits II: Currents & Circuits v 0.3 R B + − R A + − R C (a) (b) Figure 4: Two different circuits: (a) a battery with a single resistor, and (b) a battery with two resistors identical to the one in (a). Current through resistor A: Current through resistor B: Current through resistor C: Question 1.11 Do the measured values of the currents in resistors A, B and C agree with the ranking that you predicted? If not, can you identify what assumption(s), if any, you have now shown to be false? Question 1.12 Compare the amount of current produced by a battery which is connected to a single resistor, as in Fig. 4(a), to the amount of current produced when the battery is connected to two resistors, as in Fig. 4(b). How does the presence of the second resistor affect the current in the circuit? Explain. Question 1.13 How did your observations with resistors differ from your observations with bulbs in Activity 1.2. Question 1.14 Extrapolating from your observations, write down a quantitative formula which predicts how the current in the circuit decreases as of resistors connected in series, as shown in PHYS-204:Physics II Laboratory 9
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Pre-LAB 4 Assignment Fundamentals of Circuits II: Currents ...

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