Download EE1 Energy Power Info Current Voltage

Electrical Engineering
Topic 1: Energy, Power,
Information, Current, Voltage
EGR 1301
Information and Power
• Information
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iPod / music
Digital cameras
Radio/Television
Internet/Computers
Cellular telephone
Satellites
Embedded systems
Fiber optics, lasers
• Power
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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
Electric Current
• Current  flow of positive charge
“Free” electron
Atom
Electron Flow
Current
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” (+)
A B C D E
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
 1
F  
 4
qq

 r
1
2
2
0
2
C
  8.854  10
N m
12
0
• Stored energy mental images
– Stretched rubber bands
– Compressed springs
2
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.
F
F
q1
q2
r=1m
r
 1
F  
 4
 ( 1C )( 1C )
 8.99  10 N  2.02  10 lbs

 (1m)
9
2
0
q1=q2=-1C
9
Voltage
1J
1V 
1C
• 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
Voltage
1J
1V 
1C
dq
i
dt
• 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
120 VAC
100s *15 A(C / s )  1500 C
120 V ( J / C ) *1500 C  180,000 J
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
Voltage * Current 
Energy Coulomb
*

Coulomb
time
Energy
Joule

 1 Watt
time
second
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.