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Unformatted text preview: Intro to ECE Design Drs. Butera/Williams Module: Volts and Amps Objectives Upon completion of this module, you should be able to: define voltage, current, and charge for DC circuits; describe the roles of voltage and current in electronic circuits; specify a DC power supply or battery source for a DC circuit; and solve simple DC circuits with switches and resistors. What makes it go? Electricity makes things happen by moving charge down conductors. For most engineered applications, the flow of charge is moving electrons down wires and connectors and through circuit elements. Electronic circuits is the study of designing components to manipulate the flow of charge to accomplish a task, such as lighting a light or amplifying a sound. Electric circuits are both designed an analyzed in terms of two physical quantities that are co- dependent upon one another: voltage and current . Voltage is a measure of the potential force available to move charge. Current is a measure of the flow of moving charges. Charges can have both positive and negative sign. In a continuous conductive material, positive charges flow from a higher potential to a lower potential. While current flow is ultimately what enables circuits to perform their actions, voltage is the quantity that is most easily controlled, measured and passed between electronic circuits. Definitions, conventions, and units The unit of charge is a coulomb (C). A single electron has a charge of 1.6 10- 19 C. The mathematical symbol for charge is q . The unit of voltage is volts (V). The mathematical symbol for volts is V . The unit of current is amps (A). The mathematical symbol for current is I . Current is a measure of the rate of flow of electrons: 1 amp = 1 coulomb/second. While the electrons flowing in circuits have negative charge, the standard convention is to define it in terms of the direction of flow of positive charge. In virtually all of your ECE courses, the direction of current flow used in class and on your exams is actually the opposite direction of how the electrons are actually moving! While the concepts of voltage and current will be used throughout this course, we will rarely use the term coulomb. Charge storage ability (for example, by a battery) is usually described in terms of amp-hours (A h). An amp-hour is a scaled version of coulombs (see problem c 2010, ROBERT J. BUTERA, JR. AND DOUG WILLIAMS PAGE 1 Intro to ECE Design Drs. Butera/Williams Module: Volts and Amps Prefix Value Name p 10- 12 pico n 10- 9 nano 10- 6 micro m 10- 3 milli k 10 3 kilo M 10 6 mega G 10 9 giga Table 1: SI Prefixes sets) but is more intuitive to work with. For example, a battery that stores 3 amp-hours is potentially capable of sourcing 6 amps of current for 30 minutes (or 3 amps for 1 hour, etc)....
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- Fall '08