8 electrical engineering permission granted to reproduce for educational use only.©...

8

Electrical Engineering

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

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



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– 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



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

321

1111

RRR

RT


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



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

Design


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– Copper– Aluminum– Silver – Gold

• Different configurations• American Wire Gauge (AWG) system determines

size


Control Components

• Insulators• Resistors• 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



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



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


Meters

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

Tools


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


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