Electrical Engineering 8 Electrical Engineering

Objectives Define electrical engineering. Explain the secondary and college level education requirements for employment in the electrical engineering profession. Explain how electrons move on an atomic level. Describe the characteristics of voltage, current, resistance, and power. Explain Ohm’s law and use it to solve for values in a circuit. Identify the operation and application of common electronic components such as resistors, switches, capacitors, diodes, and transistors.

About Electrical Engineering Engineering field that deals with electricity and electronics Electrical engineers design, build, and test electrical devices and facilities About 21% of all engineers are electrical engineers

Educational Requirements Bachelor’s degree in electrical engineering Higher degrees often required for higher level positions Coursework in electricity, electronics, chemistry, biology, physics, and higher level math and statistics Associate’s degree required for electrical technicians

Professional Organization Institute of Electrical and Electronics Engineers (IEEE) Broadest professional society for electrical engineers Over 375,000 members Dedicated to advancing technological innovation and excellence through publications, conferences, standards, and activities

Electricity on the Atomic Level Electrons, protons, neutrons Valence shell Electron movement Electrically charged atoms are called ions Goodheart-Willcox Publisher

Static Electricity Excess of charge on object’s surface Many industrial applications Electrostatic precipitator Used to remove particles from air Charged particles stick to collection plates with opposite charge

Electricity Through Conductors Negative to positive flow using electron flow theory Move slowly, but the effective speed is about the speed of light Goodheart-Willcox Publisher

Sources of Electricity Some form of energy is converted into electrical energy Three sources of electricity Magnetism Chemical action Solar cells

Law of Conservation of Energy States that energy cannot be created or destroyed Energy can only be converted from one form to another

Magnetism Generators produce electricity by changing mechanical energy to electrical energy Voltage induced in wire when magnet passes Current induced in conductor of generator Steam, water, or wind turns turbines, creating motion that spins generators

Chemical Action Cells use chemical action to create electricity Batteries connect multiple cells Electrodes of different materials has voltage created between them Two types of cells Primary cells Secondary cells

Solar Cells Use light to create electricity Semiconductors with positive and negative layers absorb some light energy Energy causes electrons to flow in form of current Cells can power devices and houses

Characteristics and Measurements Generated electricity has certain characteristics that can be used in different ways Engineers must understand characteristics and how to measure them Voltage Current Resistance

Voltage Amount of pressure causing flow of electrons Expressed as electromotive force (EMF) Also called potential difference because it describes difference in charge from one place to another Measured in volts

Current Measure of electrons per unit time Also called amperage Measured in amperes (amps) One ampere is one coulomb of charge passing a point in one second One coulomb equals 6.24  1018 electrons

Polarity Refers to positive or negative condition at power supply terminal Direct current (dc) occurs when polarity is constant and current flows in only one direction Alternating current (ac) occurs when polarity changes back and forth from positive to negative, causing current to change direction

Resistance Opposition to current flow Measured in ohms (Ω) Current flow limited and voltage divided by resistors Resistant materials are insulators Inversely proportional to current

Power The rate at which work is done or amount of work done based on period of time Electrical power is product of voltage and current Measured in watts One watt is one volt moving one coulomb of electricity in one second

Laws Ohm’s law Watt’s law Discovered by George Ohm Describes relationship between voltage, current, and resistance Watt’s law Power equals effort multiplied by rate Used to find any one of three values when two are known

Basic Circuits Series circuits Parallel circuits Series-parallel combination circuits

Series Circuits One path for current flow Total voltage equals sum of drops across all loads Total resistance equals sum of resistance of each load Current remains constant throughout Goodheart-Willcox Publisher

Parallel Circuits Multiple paths for current flow Total voltage is equal to the voltage across each branch Total current is equal to the sum of branch currents

Series-Parallel Combination Circuits Circuits with characteristics of both series and parallel Parallel parts must be broken down and studied as if they were series elements Goodheart-Willcox Publisher

Design Schematics Schematic symbols are used to show components in circuit drawings Schematic diagrams use symbols and lines to connect components Often used in building and troubleshooting circuitry

Circuit Components Each component must be understood Understanding is necessary for design and troubleshooting Three main types of components Conductors Control components Output components

Conductors Materials have low resistance Different configurations Copper Aluminum Silver Gold Different configurations American Wire Gauge (AWG) system determines size

Control Components Insulators Transistors Resistors Capacitors Variable resistors Switches Diodes Zener diodes Transistors Capacitors Integrated circuits (ICs) Semiconductors Sensors

Insulators Very high resistance Do not conduct electricity under normal circumstances Keep electricity confined to desired path Plastic Rubber Dry wood/paper Glass/ceramics Mica

Resistors Limit current flow and divide voltage Most are made from carbon Color coding system marks the value of resistors Goodheart-Willcox Publisher

Variable Resistors Vary amount of resistance in dimmer switches and fan speed switches Two terminals and wiper, which changes amount of resistive material between terminals Represented by arrow symbol

Switches Open and close circuits Change direction of flow Characterized by type of switch, number of poles, and number of throws SPST switch can turn current on or off to circuit SPDT switch can direct current in one direction or other

Diodes Standard diodes allow current flow in only one direction Have two electrodes Anode is made of positive semiconductor material Cathode is made of negative semiconductor material Current flows in forward bias condition only Can be used as rectifiers

Zener Diodes Zener diodes are wired in reverse bias Block current until voltage reaches certain level Keep voltage at constant level Used as voltage regulators

Transistors Used as solid state switches and amplifiers Perform switching function without moving parts Bipolar transistors have three junction points Emitter Base Collector Can also be used as amplifiers

NPN and PNP Transistors Goodheart-Willcox Publisher

Capacitors Store and discharge electricity very quickly Smooth out variations in voltage Two conductive plates separated by thin insulator called dielectric Ceramic disc and electrolytic Can maintain charge long after power source is removed

Integrated Circuits (ICs) Multiple electrical circuits etched into thin layer of silicon Dot or notch on outside of chip is used for orientation Can be sensitive to static Common example is 555 timer

Semiconductors Materials with conductive capabilities between that of conductors and insulators Silicon is most common type Used in different components Transistors Diodes Solar panels Integrated circuits

Sensors Create an electrical signal based on environmental conditions Signal changes as environmental conditions change Common example is electronic thermostats

Output Components Incandescent lamps Gas discharge lamps Fluorescent lamps Compact fluorescent lamps (CFLs) Light-emitting diode (LED) lamps Motors

Incandescent Lamps Creates light when current flow causes tungsten filament to become so hot it glows All air inside glass globe is evaluated and sometimes replaced with argon Traditional incandescent bulbs are being phased out

Gas Discharge Lamps Ionized glass and free electrons cause gas to glow and create light Neon lamps are example, but other gases may be used Resistor must be placed in series with light to limit current flow

Fluorescent Lamps Long glass tube coated on inside with phosphorous and filled with inert gas and mercury Electrical current passed through mercury causes ultraviolet light, which causes phosphorous to glow Use much less electricity than incandescent lamps

Compact Fluorescent Lamps (CFLs) Work on same principle as fluorescent lamps but fit into standard light socket Use about 75% less energy than incandescent lamps Last up to ten time longer than incandescent lamps

Light-Emitting Diode (LED) Lamps Create light by wiring semiconductor material in forward biased position Forward biased direct current passes through semiconductor in LED casing, and light is emitted Low cost, efficient, and long lasting

Motors Convert electrical energy into mechanical energy Electromagnet spins until its north pole lines up with south pole of permanent magnet Polarity of electromagnet reverses, causing it to keep rotating

Component Platforms Circuit boards Solderless breadboards Electronic circuit simulation

Circuit Boards Commonly known as printed circuit boards (PCBs) Copper track laid on fiberglass Electronic components are soldered to copper track

Solderless Breadboards Ideal for experimentation Can be used to test circuits before they are constructed Components and leads can easily be added and removed because no soldering is required

Electronic Circuit Simulation Can be used to simulate performance of circuitry without having to build circuit Components are laid out on-screen Software shows how circuits would work Problems can be identified early on

Tools Meters Ammeters Voltmeters Ohmmeters Volt-ohm-milliammeters (VOM) Continuity tester Oscilloscope

Troubleshooting First step may be to test voltage Continuity tester or ohmmeter may be used to ensure continuity exists Test to see if diode conducts in forward bias and not reverse LEDs can be tested by applying voltage directly

Electrical Engineering in Action Hybrid cars Combine internal combustion engine and batteries Regenerative braking Increased fuel mileage Goodheart-Willcox Publisher