advertisement

Chapter 1: Introduction 1 Outlines 1. Recognize interrelationships of electrical engineering with other fields of science and engineering. 2. List the major subfields of electrical engineering. 3. List several important reasons for studying electrical engineering. 2 4. Define current, voltage, and power, including their units. 5. Calculate power and energy, as well as determine whether energy is supplied or absorbed by a circuit element. 6. State and apply basic circuit laws. 7. Solve for currents, voltages, and powers in simple circuits. 3 Electrical systems have two main objectives: z To gather, store, process, transport, and present information z To distribute and convert energy between various forms 4 Electrical Engineering Subdivisions z Communication systems z Computer systems z Control systems z Electromagnetics z Electronics z Photonics z Power systems z Signal processing z (Circuit design) z (Biomedical engineering) 5 Why Study Electrical Engineering? zBecause it is everywhere,… 6 7 Electrical Current Electrical current is the time rate of flow of electrical charge through a conductor or circuit element. The units are amperes (A), which are equivalent to coulombs per second (C/s). 8 Electrical Current dq (t ) i (t ) = dt t q (t ) = ∫ i (t )dt + q (t0 ) t0 9 10 11 Direct Current Alternating Current When a current is constant with time, we say that we have direct current, abbreviated as dc. On the other hand, a current that varies with time, reversing direction periodically, is called alternating current, abbreviated as ac. 12 . 13 14 15 Voltages The voltage associated with a circuit element is the energy transferred per unit of charge that flows through the element. The units of voltage are volts (V), which are equivalent to joules per coulomb (J/C). 16 17 18 19 POWER AND ENERGY p(t ) = v (t )i (t ) t2 w = ∫ p(t )dt t1 20 21 22 KIRCHHOFF’S CURRENT LAW zThe net current entering a node is zero. zAlternatively, the sum of the currents entering a node equals the sum of the currents leaving a node. 23 24 25 zpp. 19 zFig. 1.18 26 Series Circuits 27 KIRCHHOFF’S VOLTAGE LAW The algebraic sum of the voltages equals zero for any closed path (loop) in an electrical circuit. 28 29 30 31 32 Find voltages Find series/parallel connection 33 34 35 36 37 38 Resistors and Ohm’s Law a b v = iR vab = iab R 39 Conductance 1 G= R i = Gv 40 Resistance Related to Physical Parameters R= ρL A 41 Voltage, current and power 42 43 44 Using KVL, KCL, and Ohm’s Law to Solve a Circuit 45 15 V iy = =3A 5Ω ix + 0.5ix = i y ix = 2 A 46 v x = 10ix = 20 V Vs = v x + 15 Vs = 35 V 47 Problem Set z6, 14, 19, 23, 28, 33, 48, 57 48