electrical engineering topic 1: energy, power, information, current, voltage
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Electrical Engineering Topic 1: Energy, Power, Information, Current, Voltage. EGR 1301. Information iPod / music Digital cameras Radio/Television Internet/Computers Cellular telephone Satellites Embedded systems Fiber optics, lasers. Power Lighting/Appliances Motors Heating RADAR - PowerPoint PPT PresentationTRANSCRIPT
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.