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# exp04 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of...

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E04-1 MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Physics 8.02 Experiment 4: RC Circuits OBJECTIVES 1. To explore the time dependent behavior of RC Circuits 2. To understand how to measure the time constant of such circuits PRE-LAB READING INTRODUCTION In this lab we will continue our investigation of DC circuits, now including, along with our “battery” and resistors, capacitors (RC circuits). We will measure the relationship between current and voltage in a capacitor, and study the time dependent behavior of RC circuits. The Details: Capacitors Capacitors store charge, and develop a voltage drop V across them proportional to the amount of charge Q that they have stored: V = Q/C . The constant of proportionality C is the capacitance (in Farads = Coulombs/Volt), and determines how easily the capacitor can store charge. Typical circuit capacitors range from picofarads (1 pF = 10 -12 F) to millifarads (1 mF = 10 -3 F). In this lab we will use microfarad capacitors (1 μ F = 10 -6 F). RC Circuits Consider the circuit shown in Figure 1. The capacitor (initially uncharged) is connected to a voltage source of constant emf E . At t = 0, the switch S is closed. Figure 1 (a) RC circuit (b) Circuit diagram for t > 0 In class we derived expressions for the time-dependent charge on, voltage across, and current through the capacitor, but even without solving differential equations a little (a) (b)

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