W091BLLab06 - Physics 1BL CURRENT AND RESISTANCE Winter...

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C URRENT AND R ESISTANCE Winter 2009 Page 1 Introduction In this lab we will examine the concepts of electric current and potential in a circuit. We first look at devices (like batteries) that are used to generate electrical energy that we can use in circuits. Then we consider how the current through certain circuit elements depends on the voltage across them. Finally we show how the electrocardiogram can give information about electrical activity inside the human heart. You should review chapter 17 of Serway and Faughn before coming to lab. Pre-lab questions: You have a circuit consisting of six 1.5 V D-cell batteries in series, some wires, and a light bulb. The bulb is lit and the current flowing through the bulb is 0.35 A. You may assume that all of the voltage drop occurs in the light bulb. a) What is the resistance of the bulb? b) Taking the negative terminal of the first battery as 0.0 V, what is the electrical potential energy of an electron leaving the negative battery terminal? What is the electrical potential energy of the electron as it re-enters the sixth battery at the positive terminal? How much energy has the electron gained or lost as it moved around the circuit? In which part of the circuit did it lose the energy? (Hint: Where does the voltage of the electrons change?) c) How many electrons enter and leave the light bulb every second? What is the total gain or loss of energy for all the electrons in the light bulb in one second? Calculate this by comparing the energy of an individual electron as it enters the light bulb vs. its energy as it leaves. d) Using power P = I ( Δ V ) for the bulb, what is the power consumed by the bulb? e) Compare the energy change per second of the electrons and the power consumed by the bulb. Should they be the same? A. Group Activity: After your group has answered each of these questions, call your TA over to discuss them. A1 . Your TA gives you a capacitor and tells you it is charged. How can you determine if this the capacitor really is charged? What equipment would you need and what measurements would you need to make? A2 . Now suppose you connect a wire between the two terminals of the charged capacitor. Does the charge in the wire flow (a) from the positive plate to the negative plate, (b) from the negative plate to the positive plate, or (c) both of these? Have you done any experiments in this lab to demonstrate this? A3 . Describe a situation in which both positive and negative charge carriers are responsible for an electrical current. A4 . Suppose you connect one plate of a charged capacitor to one terminal of a light bulb. Then connect the other terminal of the bulb to the other capacitor plate. Figure 1 shows the circuit. Figure 1
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W091BLLab06 - Physics 1BL CURRENT AND RESISTANCE Winter...

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