Electrical EngineeringTopic 1: Energy, Power, Information, Current, Voltage

EGR 1301

Information and Power

• Information– iPod / music– Digital cameras– Radio/Television– Internet/Computers– Cellular telephone– Satellites– Embedded systems– Fiber optics, lasers

• Power– Lighting/Appliances– Motors– Heating– RADAR– Welding &

manufacturing– On grid / off grid– EMP

Electricity Basics

• Charge– The smallest unit of charge is that of an

electron– Flowing charge is “Current”– Accumulated charge produces “Voltage”

Electrical Conductors

• Metallic bond– Electrons are shared– Valence electrons

form “cloud” or “sea” of electrons

– Electrons are free to flow

– Causes metals to be good conductors

+ + +

+ + +

+ + +

Electrical Insulators

• Covalent bond– Valence electrons are

shared– BUT have to break

bond in order for electrons to flow

• Ionic bond– Valence electrons are

transferred– Charge must be

transferred by movement of entire ion

shared electrons from carbon atom

shared electrons from hydrogen atoms

H

H

H

H

C

CH4

Na (metal) unstable

Cl (nonmetal) unstable

electron

+ - Coulombic Attraction

Na (cation) stable

Cl (anion) stable

Electric Current

• Current flow of positive charge

“Free” electron

Atom

Electron Flow

Current

A B C D E

Electric Current

• Hole concept used to explain current flow– Hole = absence of an electron– An electron (-) removed from a neutral atom

leaves behind a “hole” (+)

Electric Current

• 1 “Coulomb” of charge is 6,241,506,360,000,000,000 electrons

• If 1 Coulomb flows through a wire in 1 second, we say the current is 1 ampere or 1 “amp”

• Current always “flows through”

Current Magnitudes

• Brain cell synaptic currents 10-13 A

• Integrated circuits currents 10-4 A

• Threshold of human sensation 10-3 A

• Causes ventricular fibrillation 10-1 A

• Household appliances 10 A

• Large industrial equipment 100 A

• Lightning bolt 1000 A

Electrostatic Forces

• Electrostatic force gives rise to stored energy

• Stored energy mental images– Stretched rubber bands– Compressed springs

2

2

12

0

2

21

0

10854.8

4

1

mN

C

r

qqF

Energy

• “It is important to realize that in physics today, we have no knowledge what energy is.” – Richard Feynman, Nobel Lauriat physicist

• Energy is the “stuff” that gets work done– Units of Joules, or foot pound, or calorie, or BTU, or kilowatt

hour, or horsepower, etc.

• “For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.” Richard Feynman

• Can be thought of as a unit of exchange like money

Power

• Power: the rate at which energy flows from one place to another– Units: Joules/second (also called a Watt)– Helpful to think of a Watt as an energy unit per time

unit– Like “mach one” is a certain number of miles per

hour

• Kilowatt = 1000 watts

• 1 horsepower = 745.7 watts

Electrostatic Force Example

• Example: Calculate the force on each handful of electrons that “electric man” is holding.

r

F F

q1 q2 q1=q2=-1C

r=1m

lbsNm

CCF 99

2

0

1002.21099.8)1(

)1)(1(4

1

Voltage

• Voltage arises from accumulated charge being separated

• Opposite charges attract– Positive likes negative– Energy is required to separate them

• Like the ends of a stretched rubber band• Rubber bands can be stretched to different lengths

• “Voltage” is a measure of how much energy each coulomb of charge contains

CJ

V11

1

Voltage

• 1 “volt” means each Coulomb of charge can release 1 Joule of energy– A 12 Volt battery will produce 12 Joules of

energy for every coulomb of electrons delivered

CJ

V11

1

J C CJV

C sCAs

000,1801500*)/(120

1500)/(15*100

dt

dqi

120 VAC

Voltage

• Voltage exists between two points, – NOT at an individual point

• The earth is a common reference point– “Ground”– Voltages with respect ground are like rubber

bands with one end on the ground

Power

• Remember, power is the rate at which energy is transferred

• Electric Power is found by multiplying voltage and current

Watt1second

Joule

time

Energytime

Coulomb*

Coulomb

Energy

Current*Voltage

Power

• Question: How much power is supplied to a belt sander that draws 15 amps using “wall” voltage?

• Answer: 120 Volts x 15 Amps = 1800 Watts

• 1800 W = 1.8 kW

AC, DC, and all that

• DC stands for “direct current” and means the voltage and current are constant– All batteries supply DC power– “Cigarette Lighter Power” is DC

• AC stands for “alternating current” and means that the voltage and current “alternate” back and forth

• Grid-supplied electric power is AC, cycling 60 times every second, or at 60 Hz.