Circuit_Variables

# Circuit_Variables - Chapter 1 Circuit Variables 1.1...

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Chapter 1: Circuit Variables 1.1 Electrical Engineering: An Overview Electrical Engineers are concerned with the design, analysis, and operation of systems involving electrical signals. Examples: Communications/signal engineering Computer systems Control systems/robotics Power systems Microelectronics Theoretical Basis for Electrical Engineering: Electromagnetics and Maxwell’s Equations . We will not deal with this topic here. Instead we will talk about a specialization of electromagnetics… Circuit Theory is an important special case of electromagnetics. It is appropriate where the spatial dimensions of the electrical system are small compared with the wavelength of an electromagnetic signal, i.e., where the shape of the circuit does not matter. 1

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1.2 Units We will use the International System of units: Length: meters (m) Mass: kilogram (kg) Time: second (s) Current: Ampere (A) Temperature: Kelvin (K) Also: 1 Ampere is the current that, maintained in two straight, parallel, infinite conductors of negligible circular cross section placed 1 m apart in vacuum, would produce a force between the conductors of 2 x 10 -7 N/m. The Coulomb is a unit of charge derived from the Ampere; more below. 1.3 Circuit Analysis: An Overview Idea: We want to be able to make quantitative predictions of electrical circuit behavior. We do this using idealized interconnections of circuit elements called circuit models . Modeling is an important concept: we will use simple components (resistors, batteries, capacitors…) to construct models of electrical systems. These models help us think about and design real electrical systems. They tell us how the system will behave if we make changes to it, for example. The diagram to the right is a circuit model for a flashlight; we will be using it in the next chapter to discuss basic circuit analysis concepts. 2 v battery R case R bulb
β i B v o R B1 R B2 R E R C v CE i C i s i E i B This is a circuit model taken from the text book, Chapter 2. We will have a few things to say about it in class… 3

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1.4 Voltage and Current Voltage and current are the important variables for electrical circuits. Before discussing them, we look at a more fundamental concept: charge . Charge is a basic property of matter. The smallest “piece” of charge is the charge on an electron, with magnitude q = 1.6 x 10 -19 Coulombs (Coul). We find that. .. There are two types of charge: positive and negative; Like charges (i.e., both positive or both negative) repel one another, while opposites attract. Voltage and current arise from the phenomenon of charge. To separate charges from one another requires that we exert energy, and results in the presence of a potential, or voltage. Separation of charge
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Circuit_Variables - Chapter 1 Circuit Variables 1.1...

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