1.1 Overview of Electrical Engineering

Transcription

1 1.1 Overview of Electrical Engineering

2 Figure 1.1 Pressure versus time for an internal combustion engine experiencing knock. Sensors convert pressure to an electrical signal that is processed to adjust ignition timing for minimum pollution and good performance.

3 1.2 Circuits, Current, and Voltages Figure 1.2 The headlight circuit. (a) The actual physical layout of the circuit. (b) The circuit diagram.

4 Figure 1.3 An electrical circuit consists of circuit elements, such as voltage sources, resistances, inductances, and capacitances, connected in closed paths by conductors. Figure 1.4 Current is the time rate of charge flow through a cross section of a conductor or circuit element.

5 Figure 1.5 Plots of charge and current versus time for Example 1.1. Note: The time scale is in milliseconds (ms). One millisecond is equivalent to 10 3 seconds.

6 Figure 1.6 In analyzing circuits, we frequently start by assigning current variables i 1, i 2, i 3, and so forth. Figure 1.7 Examples of dc and ac currents versus time.

7 Figure 1.8 Ac currents can have various waveforms. Figure 1.9 Reference directions can be indicated by labeling the ends of circuit elements and using double subscripts on current variables. The reference direction for i ab points from a to b. On the other hand, the reference direction for iba points from b to a.

8 Figure 1.10 Energy is transferred when charge flows through an element having a voltage across it. Figure 1.11 If we do not know the voltage values and polarities in a circuit, we can start by assigning voltage variables choosing the reference polarities arbitrarily. (The boxes represent unspecified circuit elements.)

9 Figure 1.12 The voltage v ab has a reference polarity that is positive at point a and negative at point b. Figure 1.13 The positive reference for v is at the head of the arrow.

10 1.3 Power and Energy Figure 1.14 When current flows through an element and voltage appears across the element, energy is transferred. The rate of energy transfer is p = vi.

11 Figure 1.15 Circuit elements for Example 1.2.

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13 Figure 1.16 Circuit element for Example 1.3.

14 Figure 1.17 See Exercise Kirchhoff s Current Law

15 Figure 1.18 Partial circuits showing one node each to illustrate Kirchhoff s current law. Figure 1.19 Elements A, B, C, and D can be considered to be connected to a common node, because all points in a circuit that are connected directly by conductors are electrically equivalent to a single point.

16 Figure 1.20 Elements A, B, and C are connected in series. Figure 1.21 See Exercise 1.7.

17 Figure 1.22 Circuit for Exercise Kirchhoff s Voltage Law

18 Figure 1.23 In applying KVL to a loop, voltages are added or subtracted depending on their reference polarities relative to the direction of travel around the loop. Figure 1.24 Circuit used for illustration of Kirchhoff s voltage law.

19 Figure 1.25 In this circuit, conservation of energy requires that v b = v a + v c. Figure 1.26 In this circuit, elements A and B are in parallel. Elements D, E, and F form another parallel combination.

20 Figure 1.27 For this circuit, we can show that v a = v b = v c. Thus, the magnitudes and actual polarities of all three voltages are the same. Figure 1.28 parallel. Analysis is simplified by using the same voltage variable and reference polarity for elements that are in

21 Figure 1.29 Circuit for Exercises 1.9 and Introduction to Circuit Elements

22 Figure 1.30 Independent voltage sources. Figure 1.31 We avoid self-contradictory circuit diagrams such as this one.

23 Figure 1.32 Dependent voltage sources (also known as controlled voltage sources) are represented by diamondshaped symbols. The voltage across a controlled voltage source depends on a current or voltage that appears elsewhere in the circuit. Figure 1.33 Independent current sources.

24 Figure 1.34 Dependent current sources. The current through a dependent current source depends on a current or voltage that appears elsewhere in the circuit. Figure 1.35 Voltage is proportional to current in an ideal resistor. Notice that the references for v and i conform to the passive reference configuration.

25 Figure 1.36 If the references for v and i are opposite to the passive configuration, we have v = Ri. Figure 1.37 We construct resistors by attaching terminals to a piece of conductive material.

26 Figure 1.38 the length. Resistors often take the form of a long cylinder (or bar) in which current enters one end and flows along

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28 Figure PA Introduction to Circuits

29 Figure 1.39 A circuit consisting of a voltage source and a resistance.

30 Figure 1.40 Circuit for Example 1.6.

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32 Figure 1.41 Circuit for Example 1.7. Figure 1.40 Circuit for Example 1.6.

33 Figure 1.41 Circuit for Example 1.7. Figure 1.42 Circuit for Exercise 1.14.

34 Figure 1.43 Circuit for Exercise 1.15.