© 2005 Baylor University EGR 1301 Slide 1 Lecture 21 Introduction to Engineering Approximate...
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Transcript of © 2005 Baylor University EGR 1301 Slide 1 Lecture 21 Introduction to Engineering Approximate...
Slide 1 © 2005 Baylor University EGR 1301
Lecture 21Introduction to Engineering
Approximate Running Time - 23 minutesDistance Learning / Online Instructional Presentation
Presented byDepartment of Mechanical Engineering
Baylor University
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Slide 2 © 2005 Baylor University EGR 1301
Lecture 21:Electrical Engineering Topic 1
Voltage and Current
Professor Brian Thomas Speaking
Slide 3 © 2005 Baylor University EGR 1301
Outline
• Electrical Engineering: Information and Power
• Electricity Basics– Charge– Current, Voltage, – Power– AC, DC, grid power
Slide 4 © 2005 Baylor University EGR 1301
Information and Power
• Information– Radio– Television– Internet– Cellular telephone– Satellites– Embedded systems– Fiber optics, lasers
• Power– Lighting– Appliances– Motors– Heating– Welding &
manufacturing– On grid / off grid– EMP
Slide 5 © 2005 Baylor University EGR 1301
Electricity Basics
• Charge– The smallest bit of charge is the charge of an
electron– Charge flowing is called “Current”– Charge accumulated produces “Voltage”
Slide 6 © 2005 Baylor University EGR 1301
Electric Current
“Free” electron
Atom
• Electrons are free to flow in metals and other “conductors”
• Materials where charge may not flow are “insulators”
• An electron removed from a neutral atom leaves behind a “hole”
• By convention: electrons have negative charge, protons (and holes) have positive charge
Slide 7 © 2005 Baylor University EGR 1301
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”
Slide 8 © 2005 Baylor University EGR 1301
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)
Slide 9 © 2005 Baylor University EGR 1301
Electrostatic Forces
• Electrostatic force gives rise to stored energy
• Stored energy mental images– Stretched rubber bands– Compressed springs– Water pressure (or height
of column of water)
2
212
0
221
41
m-N10*854.8
)(0
C
r
qqF
Slide 10 © 2005 Baylor University EGR 1301
Electrostatic Force Example
f
2
m-N
12
2
20
21
lbbillion 2.02 Nbillion 99.8
)m1(10*854.8*4
1
)1(4
)1)(1(
1
1
if electrons, of
handfuleach on force theCalculate :Example
2
2
F
C
m
CCF
mr
Cqq
C
1q 2q
F F
r
Slide 11 © 2005 Baylor University EGR 1301
Voltage
• Voltage arises from accumulated charge being separated
• Opposite Charges Attract– Positive likes negative and visa versa – Energy is required to keep them apart
• Like the ends of a rubber band• Rubber bands can be stretched to different lengths
• “Voltage” is a measure of how much energy each coulomb of charge contains
Slide 12 © 2005 Baylor University EGR 1301
• 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
Voltage
JoulesCqjoulesVolts
CoulombscoulombsAmps
000,180 1500*)/( 120
1500sec)/(15sec*100
dt
dqi
120 VAC
Slide 13 © 2005 Baylor University EGR 1301
• 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
Voltage
Slide 14 © 2005 Baylor University EGR 1301
Power
• 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
Slide 15 © 2005 Baylor University EGR 1301
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
Slide 16 © 2005 Baylor University EGR 1301
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.