A long time ago, in a galaxy far, far away…. 1-1

Chapters I & II CIRCUIT VARIABLES AND ELEMENTS The Empire is bad, mmkay? But we’re not here to talk about that. We’re here to learn circuits! So lets get started! 1-2

Agenda Overview of Electrical Engineering This Particular Course SI Units and Engineering Notation Voltage Current Energy Power

Chapter Goals Circuit Elements Circuit Theory Constructing a Circuit Model Circuit Analysis with Dependent Sources

Electrical Engineering Subfields Communication - Telephones, radios, microwave communications. Conversion, transmission, and processing of analog electromagnetic signals Computer - EE’s build analog devices that deal with discrete voltage levels (bits). Control - Use electrical signals to regulate processes. Cruise control, elevators, rockets. Power - Generating and distributing electrical power. Signal Processing - MRI’s, CAT scans (image processing) Converting signals to an intelligible form. (Big field now is Digital Signal Processing (DSP) where analog signals are first digitized, then processed digitally.) 1-5

THE COURSE IN A NUTSHELL 1-6

The Course in a Nutshell First course in engineering analysis – we are learning engineering analysis methodology – Methodology is NOT limited to just circuits How to construct, analyze and solve mathematical circuit models, in particularly interested in: – Voltage, Current, Energy, Power 1-7

!!MODELING!! Modeling is and important engineering skill Perhaps THE MOST IMPORTANT engineering skill Kinds of engineering models – Circuits, drawings, system diagrams, process flow charts 1-8

Important SI Units QuantityUnitSymbolFormula frequencyhertzHZ1/s forcenewtonNKg*m/s^2 energy or workjouleJN*m powerwattWJ/s chargecoulombCA/s potentialvoltVJ/C resistanceohmΩV/A

Engineering Notation 1-10 Engineers mostly use the powers divisible by three, and keep the base number between 1 and ex) seconds= 4 x s = 44 µs ex) volts = 87.6 x 10 6 V = 87.6 MV (typically rounded to 3 sigfigs, that’s 1%!!) 5

VOLTAGE CURRENT ENERGY POWER 1-11

Voltage The energy of charge separation, or, The work required to separate charges volts = Joule/Coulomb Voltage = Energy/Charge Analogous to water pressure 1-12

Current The flow rate of charged particles: Amp = Coulomb/Second Analogous to water flowing 1-13

Energy Difficult to intuitively define, actually. Richard FeynmanRichard Feynman, "It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount.". 1-14

Energy: Lets’ try again Comes in many interchangeable forms. Easiest form to understand is probably WORK Work = Force * Displacement [J = N*m] Other forms of energy are Heat, kinetic, chemical, electrical, nuclear, etc 1-15

Power The RATE of energy use: Watt = Joule / Second Can be high powered like a rocket Use up 1 gallon of gas in 1 second Can be low powered like a scooter Use up 1 gallon of gas in 1 hour 1-16

More about Power and Energy Energy and power are always CONSERVED That is, they can change form but are never created or destroyed (in classical Newtonian physics) (But sometimes they leave our system boundaries) p = iv p = i 2 * R p = v 2 / R 1-17

CIRCUIT ELEMENTS 1-18

Circuit Elements 1-19 Voltage sources Current sources Resistors Capacitors Inductors 2

Voltage and Current Sources 1-20 Voltage sources Direct Alternating Function-driven Independent Dependent 2

Resistors 1-21 Resist the flow of current Energy (voltage) is required to force current thru them this “voltage energy” is transformed to heat analogous to a valve like a faucet Ohms’ Law: v = iR 2

Capacitors 1-22 Stores up and releases charge (energy) depending on the change in voltage i = C dv/dt i is the “displacement current” cuz the dielectric it does not conduct current 2

Inductors 1-23 Stores up and releases (voltage) energy depending on the change in current v = L di/dt 2

CIRCUIT THEORY 1-24

Circuit Theory A Circuit is a mathematical models that approximates the behavior of an actual physical system 2.Circuit Theory is the study of electrical charges (simpler than emphasizing magnetic fields, although magnetism is a factor) 2

Some Basic Assumptions (simplifications) Electric Effects happens instantaneously throughout the system. aka “lumped parameter system” 2.The net charge on every component is always zero. 3.There is no (usually) magnetic coupling between components. 4.Conductors (usually) have no resistance 5.Elements are “ideal” – they obey our math models 2

A SIMPLE CIRCUIT MODEL 1-27

A Flashlight Circuit Model Constant ideal independent voltage source Ideal Resistor (light bulb) Ideal conductor (zero resistance) Ohm’s law applies KCL and KVL apply Power laws apply (Instructor will now do amazing mathematical things with this model)

!MODELING! Real v Ideal Constant ideal independent voltage source – Contrast with real battery Ideal Resistor (light bulb) – Contrast with real light bulb Ideal conductor (zero resistance) – Contrast with real conductor Other effects – inductance, capacitance, etc