Transcript Voltage - Mars at UMHB

Lecture 21
Introduction to Engineering
Approximate Running Time - 23 minutes
Distance Learning / Online Instructional Presentation
Presented by
Department of Mechanical Engineering
Baylor University
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Slide 1
© 2005 Baylor University
EGR 1301
Lecture 21:
Electrical Engineering Topic 1
Voltage and Current
Professor Brian Thomas Speaking
Slide 2
© 2005 Baylor University
EGR 1301
Outline
• Electrical Engineering:
Information and Power
• Electricity Basics
– Charge
– Current, Voltage,
– Power
– AC, DC, grid power
Slide 3
© 2005 Baylor University
EGR 1301
Information and Power
• Information
–
–
–
–
–
–
–
Slide 4
Radio
Television
Internet
Cellular telephone
Satellites
Embedded systems
Fiber optics, lasers
© 2005 Baylor University
• Power
–
–
–
–
–
Lighting
Appliances
Motors
Heating
Welding &
manufacturing
– On grid / off grid
– EMP
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 5
© 2005 Baylor University
EGR 1301
Electric Current
• Electrons are free to flow in metals and other
“conductors”
“Free” electron
Atom
• 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 6
© 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 7
© 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 8
© 2005 Baylor University
EGR 1301
Electrostatic Forces
• Electrostatic force gives
rise to stored energy
q1q2
F  ( 4 0 ) 2
r
1
• Stored energy mental
images
– Stretched rubber bands
– Compressed springs
– Water pressure (or height
of column of water)
Slide 9
© 2005 Baylor University
 0  8.854 *10
12
2
C
N - m2
EGR 1301
Electrostatic Force Example
Example : Calculate the force on each handful
of electrons, if
q1  q2  1 C
r 1m
F
F
q1
q2
r
(1C )( 1C )
1C 2
F

2
40 (1m)
4 * 8.854 *10 12
C2
N -m 2
(1m 2 )
F  8.99 billion N  2.02 billion lb f
Slide 10
© 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 11
© 2005 Baylor University
EGR 1301
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
i
dq
dt
120 VAC
100 sec*15 Amps(coulombs / sec)  1500 Coulombs
120 Volts( joules / q) *1500 C  180,000 Joules
Slide 12
© 2005 Baylor University
EGR 1301
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
Slide 13
© 2005 Baylor University
EGR 1301
Power
• Power is the rate at which energy is
transferred
• Electric Power is found by multiplying
voltage and current
Voltage * Current 
Energy Coulomb
*

Coulomb
time
Energy
Joule

 1 Watt
time
second
Slide 14
© 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 15
© 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.
Slide 16
© 2005 Baylor University
EGR 1301
This Concludes Lecture 20
Slide 17
© 2005 Baylor University
EGR 1301