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# exp03 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of...

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E03-1 MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Physics 8.02 Experiment 3: Ohm’s Law & DC Circuits OBJECTIVES 1. To explore the measurement of voltage & current in circuits 2. To see Ohm’s law in action for resistors 3. To learn how to translate circuit diagrams to physical circuits on a board PRE-LAB READING INTRODUCTION When a battery is connected to a circuit consisting of wires and other circuit elements like resistors and capacitors, voltages can develop across those elements and currents can flow through them. In this lab we will investigate simple circuits with only resistors in them. We will confirm that there is a linear relationship between current through and potential difference across resistors (Ohm’s law: V = IR ). The Details: Measuring Voltage and Current Imagine you wish to measure the voltage drop across and current through a resistor in a circuit. To do so, you would use a voltmeter and an ammeter – similar devices that measure the amount of current flowing in one lead, through the device, and out the other lead. But they have an important difference. An ammeter has a very low resistance, so when placed in series with the resistor, the current measured is not significantly affected (Fig. 1a). A voltmeter, on the other hand, has a very high resistance, so when placed in parallel with the resistor (thus seeing the same voltage drop) it will draw only a very small amount of current (which it can convert to voltage using Ohm’s Law V R = V meter = I meter R meter ), and again will not appreciably change the circuit (Fig. 1b). Figure 1: Measuring current and voltage in a simple circuit. To measure current through the resistor (a) the ammeter is placed in series with it. To measure the voltage drop across the resistor (b) the voltmeter is placed in parallel with it.

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