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

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Fundamentals of Circuits II: Currents & Circuits v 0.3 Transistor Socket Batteries Holders Switch Bulb Sockets Potentiometer Inductor + A B C L = 8mH − E B C + − Figure 2: One possible way of wiring the circuit in Fig. ?? on the Pasco circuit board. An Annotated picture of the Pasco circuit board can be found in the appendix of this lab handout. Activity 1.1: The Relative Brightness of Bulbs Step 1: Connect the circuits in Fig. 1, observe the relative brightness of the bulbs, and rank the bulbs in order of the brightness you actually observed. Comment from Real-Time Physics: “These activities assume identical bulbs. Differences in brightness may arise if the bulbs are not exactly identical. In this and later activities, to determine whether a difference in brightness is caused by a difference in the currents through the bulbs or by a difference in the bulbs, you should exchange the bulbs. Sometimes a bulb will not light noticeably, even if there is a small but significant current through it. If a bulb is really off, that is, if there is no current through it, then unscrewing the bulb will not affect the rest of the circuit. To verify whether a non-glowing bulb actually has a current through it, unscrew the bulb and see if anything else in the circuit changes.” Observed ranking of the brightness of the bulbs: Question 1.1 Do your observations and your predictions agree? If not, identify any assumption(s) that you have now shown to be false. PHYS-204:Physics II Laboratory 4
Fundamentals of Circuits II: Currents & Circuits v 0.3 Prediction 1.2 Consider reversing the batteries in the circuits shown in Fig. 1. What will happen to the brightness of bulbs A, B and C if the positive and negative terminals of the battery are reversed? Explain the reason(s) for your prediction. Step 2: Test your prediction by reversing the terminals of the battery in each of your circuits. Question 1.2 Did your observation agree with your prediction? Explain. Identify any assumptions(s) which you have now falsified. Question 1.3 Considering the observations you have made above, without knowing how the battery is hooked up, does the brightness of the bulbs tell you what the direction of the current is? Explain. Activity 1.2: Current in a Simple Circuit with Bulbs This activity is designed to further investigate how a bulb and a series of bulbs affects the current in a circuit. Prediction 1.3 How do you predict the currents going through each of the bulbs in Fig. 1 will compare? Write down your predicted rankings of the currents through bulbs A, B and C, and explain your reasoning. You will test your prediction by using current probes. We want the current probe to measure the current which goes through a bulb. Therefore we must connect the current probes so that the current which passes through a bulb also passes through the current probe. Study Fig. 3 and convince yourself that the the current probes there measure the currents as described in the figure caption. Real-Time Physics Comment: “In carrying out your measurements, it is important to realize that the measurements made by the current probes are only as good as their calibrations. Small differences in calibration can result in small differences in readings.” Step 1: Open the file L2A1-2 (Two Currents). You should see two sets of current axes similar to the picture below. Step 2: Zero the probes with them disconnected from the circuit. PHYS-204:Physics II Laboratory 5
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Pre-LAB 4 Assignment Fundamentals of Circuits II: Currents ...

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