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8/6/2019 3336 Lect 1-Intro
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INTRODUCTION TO CIRCUITS& ELECTRONICS
ECE 3336
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Technology & Electrical Engineering
http://c/Users/Admin/Main%20folders/Academic/Teaching/ECE%201100%20Intro%20to%20Elec%20and%20Comp%20Eng/ece%201100%20lectures/Study%20engineering%20ECE1100.pptx8/6/2019 3336 Lect 1-Intro
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Introduction to Circuits & Electronics
http://c/Users/Admin/Main%20folders/Academic/Teaching/ECE%203336/ECE3336%20Admin%20items/3336Syllabus_Fall2010.pdf8/6/2019 3336 Lect 1-Intro
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Will this course make you an electroniccircuit design wiz?
May be, not necessarily (it takes in-depthtraining and years of practice to be a circuitdesigner)
Can this course make you a smart user(informed user) of electronic circuits?
Yes, if you study hard
Is this course easy?
No
Is this course hard?
Not really
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Introduction to Circuits & Electronics
Input Output
It doessomething
useful:-information-power
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Transition from the firstindustrial revolution to the
second industrial revolution
Remember this?
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Source of water
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Fetch water
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Circuits & Electronics:to control the flow of
electrons for:
- work: power, energy
- information:communication, computation
Plumbing: control the
flow of water
molecules
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INTRODUCTION TO CIRCUITS& ELECTRONICS
ECE 3336
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ECE 3336Introduction to Circuits & Electronics
Prof. Han LeECE Dept.
Lecture Set #1
Voltage, Current, Energy and Power
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WHAT ARE CURRENT AND
VOLTAGE?
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Overview
In this part, we will cover:
Definitions of current and voltage
Hydraulic analogies to current and voltage
Reference polarities and actual polarities
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Current: Formal Definition
Current is the net flow of charges, per time, past anarbitrary plane in some kind of electrical device.
We will only be concerned with the flow of positivecharges. A negative charge moving to the right is
conceptually the same as a positive charge moving tothe left.
Mathematically, current is expressed as
dqi
dt
Current,
typically inAmperes [A]
Charge, typically inCoulombs [C]
Time, typically inseconds [s]
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The Ampere
The unit of current is the [Ampere],which is a flow of 1 [Coulomb] ofcharge per [second], or:
1[A] = 1[Coul/sec]
Remember that current is definedin terms of the flow of positivecharges.
One coulomb of positive charges per second flowingfrom left to right
- is equivalent to -
one coulomb of negative charges per second flowingfrom right to left.
Andre Marie Ampere(1775-1836)
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What is the Dealwith the Square Brackets [ and ]?
The unit of current is the
[Ampere], which is a flowof 1 [Coulomb] of chargeper [second], or:
1[A] = 1[Coul/sec]
Remember that currentis defined in terms of theflow of positive charges.
In these notes, we placeunits inside squarebrackets ([ and ]). This isdone to make it clear thatthe units are indeedunits, to try to avoidconfusion. This step is
optional. Showing unitsis important. Using thesquare brackets is notimportant, and is not
required.
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How to measure current
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Hydraulic Analogy for Current
It is often useful to think in terms of hydraulicanalogies.
The analogy here is that current is analogous tothe flow rate of water:
Charges going past a plane per time is analogous to
volume of water going past a plane in a pipe pertime.
W t fl C t
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Water flow Current
So, if we put a plane (a screen, say) across a waterpipe, and measure the volume of water that movespast that plane in a second, we get the flow rate.
In a similar way, current is the number of positive
charges moving past a plane in a current-carryingdevice (a wire, say) in a second.
The number of charges per second passing theplane for each [Ampere] of current flow is called a
[Coulomb], which is about 6.24 x 1018
electroncharges.
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Voltage: Formal Definition
When we move a charge in the presence ofother charges, the potential energy of thatcharge changes. Voltage is the change inpotential energy, per charge, as we movebetween two points; it is a potential difference.
Mathematically, this is expressed as
Voltage,
typically inVolts [V]
Energy, typically inJoules [J]
Charge, typically inCoulombs [C]
dwvdq
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What is a [Volt]?
The unit of voltage is the [Volt]. A[Volt] is defined as a [Joule perCoulomb].
Remember that voltage is defined interms of the energy gained or lost by
the movement of positive charges.
Alessandro GiuseppeAntonio Anastasio Volta
(17451827)
One [Joule] of energy is lost from anelectric system when a [Coulomb] ofpositive charges moves from onepotential to another potential that isone [Volt] lower.
Charles Augustin de Coulomb
(17361806)
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Hydraulic Analogy for Voltage
Hydraulic analogy: voltage isanalogous to height. In a gravitationalfield, the higher that water is, themore potential energy it has.
The voltage between two points
is analogous to
the change in height between twopoints, in a pipe.
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Hydraulic Analogy:Voltage and Current
height ~ voltageflow rate ~ current
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V=g h Flow mass
Power P=V x Flow mass
Power P=V x I
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Hydraulic Analogy With Two Paths
This diagram is intended toshow a water pipe that
breaks into two parts and
then combines again. The
size of the blue arrows are
intended to reflect the
amount of water flow at
that point.
Two Pipes Analogy
Water is flowingthroughthe pipes.
There is a heightdifference acrossthesepipes.
We can extend this analogy tocurrent throughand voltageacrossan electric device
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Current Through
If we have twopipes connectingtwo points, the flowrate through onepipe can bedifferent from theflow rate through
the other. The flowrate depends onthe path.
Flow rate in thesmaller pipe
is less than it is
in the
larger pipe.
Like flow rate,
current is pathdependent.
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Voltage Across
No matter whichpath you follow,the height is the
same acrossthose two points.The height doesnot depend on thepath
Height
Like height, voltageis path independent.
The heightbetween two
points does
not change
as you go
through the
two pipes.
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Polarities
It is extremely important that we know thepolarity, or the sign, of the voltages andcurrents we use. Which way is the
current flowing? Where is the potentialhigher? To keep track of these things,two concepts are used:
1. Reference polarities, and
2. Actual polarities.
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Reference Polarities
The reference polarity is a directionchosen for the purposes of keeping track.It is like picking North as your referencedirection, and keeping track of your
direction of travel by saying that you aremoving in a direction of 135 degrees. Thisonly tells you where you are going withrespect to north, your reference direction.
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Actual Polarity
The actual polarity is the direction something isactually going. We have only two possible
directions for current and voltage.
If the actual polarity is the same direction asthe reference polarity, we use a positive sign
for the value of that quantity. If the actual polarity is the opposite direction
from the reference polarity, we use anegative sign for the value of that quantity.
R l i hi b
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Relationship between
Reference Polarity and Actual Polarity
The actual polarity is the direction something isactually going. The reference polarity is adirection chosen for the purposes of keeping
track. We have only two possible directionsfor current and voltage.
Thus, if we have a reference polarity defined,and we know the sign of the value of thatquantity, we can get the actual polarity.
Example: Suppose we pick our referencedirection as up. The distance we go up is
5[feet]. We know then, that we have movedan actual distance of +5[feet] down.
The referencepolarity is up.
The actualpolarity is
down.
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Reference Polarities
Reference polarities do not indicate actualpolarities. They cannot be assigned
incorrectly. You cant make a mistakeassigning a reference polarity to a variable.
Always assign reference polarities for thevoltages and currents that you name.Without this step, these variables remainundefined. All variables must be defined ifthey are used in an expression.
Polarities for Currents
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Polarities for Currents
For current, the reference polarity is given by an arrow.
The actual polarity is indicated by a value that is associatedwith that arrow.
In the diagram below, the currents i1 and i2are not defineduntil the arrows are shown.
Use lowercase variables for current. Uppercase subscriptsare preferred. i2 i1 -3[A] 3[A]
i1 = 3[A]
i2 = -3[A]These are all different ways to show the same thing, a
current of 3 [Coulombs] per [second] of positive charges
moving from left to right through this wire.
The arrow shows a reference polarity, and the sign of the
number that goes with that arrow shows the actual
polarity.
a wire
Polarities for Voltages
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Polarities for Voltages
For voltage, the reference polarity is given by a + symbol
and a symbol, at or near the two points involved. The actual polarity is indicated by a value that is placed
between the + and - symbols.
In the diagram below, the voltages v1
and v2
are not defined
until the + and symbols are shown. Use lowercase variables for voltage. Uppercase subscripts
are preferred.
+
-
v1(t)Device
+
-
v2(t)
+
-
5[V]
+
-
-5[V]
Defining Voltages
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Defining Voltages
For voltage, the reference polarity is given by a +symbol and a symbol, at or near the two pointsinvolved.
The actual polarity is indicated by the sign of thevalue that is placed between the + and - symbols.
In the diagram below, the voltagesv1 and
v2 arenot defined until the + and symbols are shown.
In this case,
v1 = 5[V]and
v2
= -5[V].
These four labels
all mean the same
thing.
+
-
v1(t)Device
+
-
v2(t)
+
-
5[V]
+
-
-5[V]
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Why bother with reference polarities?
Students who are new to circuits oftenquestion whether this is intended just tomake something easy seem complicated.
It is not so; using reference polaritieshelps.
The key is that often the actual polarity ofa voltage or current is not known until
later. We want to be able to writeexpressions that will be valid no matterwhat the actual polarities turn out to be.
To do this, we use reference polarities,
and the actual polarities come out later.
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Overview
In this part, we will cover:
Definitions of current and voltage
Hydraulic analogies to current and voltage
Reference polarities and actual polarities
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PART 2
ENERGY, POWER, AND WHICHWAY THEY GO (INPUT OROUTPUT)
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Overview of this Part
In this part of the module, we will cover thefollowing topics:
Definitions of energy and power
Sign Conventions for power direction
Which way do the energy and power go?
Hydraulic analogy to energy and power, and
yet another hydraulic analogy
This is the definition found in most
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Energy
Energy is the ability or the capacity to do
work. It is a quantity that can take on many forms,
among them heat, light, sound, motion ofobjects with mass.
This is the definition found in mostdictionaries, although it is dangerous touse nontechnical dictionaries to definetechnical terms. For example, some
dictionaries list force and power assynonyms for energy, and we will neverdo that for this course!
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Joule Definition
The unit for energy that we use isthe [Joule] [J].
A [Joule] is a [Newton-meter].
In everything that we do in circuit
analysis, energy will be conserved. One of the key concerns in circuit
analysis is this: Is a device, object,or element absorbing energy ordelivering energy?
James Prescott Joule(1818 1889)
Isaac Newton (16431727)
http://www.energy.gov/energysources/electricpower.htm
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Electric energy generation
Air molecules
kinetic energy
Blades/turbine
kinetic energy
Electrons energy(electrical energy)
V x I
http://www.energy.gov/energysources/electricpower.htm
http://www.energy.gov/energysources/electricpower.htm
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Electric energy generation
Blades/turbine kineticenergy
Electrons energy(electrical energy)
V x I
coal + CO2 moleculeskinetic energy
H2O molecules
kinetic energy(hot steam)
H2O moleculeskinetic energy
(hot steam)
p gy g gy p
El t i tihttp://www.energy.gov/energysources/electricpower.htm
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Electric energy generation
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Electric energy generation
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Power
Power is the rate of change of the energy,with time. It is the rate at which the energy isabsorbed or delivered.
Again, a key concern is this: Is power being
absorbed or delivered? We will show a wayto answer this question.
Mathematically, power is defined as:
Power,typically inWatts [W]
Energy, typically inJoules [J]
Time, typically inseconds [s]
dwp
dt
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Watt Definition
A [Watt] is defined as a [Joule per
second].
We use a capital [W] for this unit.
Light bulbs are rated in [W]. Thus, a100[W] light bulb is one that absorbs100[Joules] every [second] that it is
turned on.
James Watt (1736-1819)
An athlete burning 1300 Wexercising
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Power from Voltage and Current
Power can be found from the voltage andcurrent, as shown below. Note that if voltage
is given in [V], and current in [A], power willcome out in [W].
dw dw dq p vidt dq dt
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Capacitor discharge
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Sign Conventions or Polarity Conventions
To determine whether power and energy aredelivered or absorbed, we will introduce signconventions, or polarity conventions.
A sign convention is a relationship betweenreference polarities for voltage and current.
As in all reference polarity issues, you cant
choose reference polarities wrong. You justhave to understand what your choice means.
Passive Sign Convention Definition
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ass e S g Co e t o e t o
The passive sign convention is when the referencepolarity for the current is in the direction of thereference voltage drop.
Another way of saying this is that when thereference polarity for the current enters the positiveterminal for the reference polarity for the voltage,we have used the passive sign convention.
Circuit Circuit
vX
+
-
iX
iYvY
+
-
Passive Sign Convention
Passive Sign Convention Discussion
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g
of the Definition
The two circuits below have reference polaritieswhich are in the passive sign convention.
Notice that although they look different, these twocircuits have the same relationship between thepolarities of the voltage and current.
Circuit Circuit
vX
+
-
iX
iYvY
+
-
Passive Sign Convention
Active Sign Convention Definition
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g
The active sign convention is when the reference polarity forthe current is in the direction of the reference voltage rise.
Another way of saying this is that when the reference polarityfor the current enters the negative terminal for the referencepolarity for the voltage, we have used the active signconvention.
Circuit Circuit
vW
+
-
iW
iZvZ
+
-
Active Sign Convention
Active Sign Convention Discussion of
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g
the Definition
The two circuits below have reference polaritieswhich are in the active sign convention.
Notice that although they look different, these twocircuits have the same relationship between thepolarities of the voltage and current.
Circuit Circuit
vW
+
-
iW
iZvZ
+
-
Active Sign Convention
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Using Sign Conventions for Power
Direction Subscripts We will use the sign conventions that we just
defined in several ways in circuit analysis. Fornow, lets just concentrate on using it to determine
whether power is absorbed, or power isdelivered.
We might want to write an expression for powerabsorbed by a device, circuit element, or other part
of a circuit. It is necessary for you to be clear aboutwhat you are talking about. A good way to do thisis by using appropriate subscripts.
. . ABS BY DEVICEp
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Using Sign Conventions for Power
Direction The RulesWe will use the sign conventions to
determine whether power isabsorbed, or power is delivered.
When we use the passive signconvention to assign referencepolarities, vigives the powerabsorbed, and vigives the powerdelivered.
When we use the active signconvention to assign referencepolarities, vigives the powerdelivered, and vigives the power
absorbed.
Using Sign Conventions for Power
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g g
Direction The Rules
We will use the sign conventions to determine whether poweris absorbed, or power is delivered.
When we use the passive sign convention to assignreference polarities, vigives the power absorbed, and vigives the power delivered.
When we use the active sign convention to assignreference polarities, vigives the power delivered, and vigives thepowerabsorbed.
PassiveConvention
ActiveConvention
Powerabsorbed
pABS= vi p ABS= -vi
Power
delivered
pDEL
= -vi p DEL
= vi
Example of Using the Power Direction
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p g
Table Step 1
We want an expression for the power absorbed by thisSample Circuit.
1. Determine which sign convention has beenused to assign reference polarities for thisSample Circuit.
Sample
Circuit
iS
vS
+
-
PassiveConvention
ActiveConvention
Powerabsorbed
pABS= vi p ABS= -vi
Powerdelivered
pDEL = -vi p DEL = vi
Example of Using the Power Direction
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p g
Table Step 2
We want an expression for the power absorbed by thisSample Circuit.
1. Determine which sign convention has been used.
2. Next, we find the cell that is of interest to ushere in the table. It is highlighted in red below.
Sample
Circuit
iS
vS
+
-
This is the active sign convention.
Passive
Convention
Active
Convention
Power
absorbedpABS= vi pABS= -vi
Power
deliveredp
DEL
= -vi p DEL
= vi
Example of Using the Power Direction
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p g
Table Step 3
We want an expression for the power absorbed by thisSample Circuit.
1. Determine which sign convention has been used.
2. Find the cell that is of interest to us here in thetable. This cell is highlighted in red.
3. Thus, we write pABS,CIR= -vSiS.
Sample
Circuit
iS
vS
+
-
Go back toOverview
slide.
This is the active signconvention.
Passive
Convention
Active
Convention
Power
absorbedpABS= vi pABS= -vi
Power
delivered
pDEL
= -vi p DEL
= vi
Example of Using the Power Direction
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p g
Table Note on Notation
We want an expression for the power absorbed by thisSample Circuit.
1. Determine which sign convention has been used.
2. Find the cell that is of interest to us here in thetable. This cell is highlighted in red.
3. Thus, we write pABS.BY.CIR= -vSiS.
Sample
Circuit
iS
vS
+
-
In your power expressions, always
use lowercase variables for power.Uppercase subscripts are preferred.Always use a two-part subscript for allpower and energy variables. Indicate
whether abs or del, and by what.
Hydraulic Analogy
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Hydraulic Analogy
The hydraulic analogy here can be used to test our rule
for finding the direction that power goes. Imagine awaterfall. A real waterfall, and a schematic waterfallare shown here.
Hydraulic Analogy
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Hydraulic Analogy
for Power Directions Test
The hydraulic analogy here can be used to test our rule for findingthe direction that power goes. Imagine a waterfall.
The waterflow is in the direction of the drop in height. Thus, this isanalogous to the passive sign convention. Thus, if we wrote anexpression for power absorbed, we would write:
pabs= vi
Since the values are positive, the power absorbed will be positive.
Does this make sense?
Height
Flow direction
Hydraulic Analogy
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Hydraulic Analogy
for Power Directions Answer
The power absorbed will be positive. Does this make sense? Yes, but only if we understand a key assumption. In circuits, when
we say energy absorbed, we mean the energy absorbed from theelectrical system, and delivered somewhere else.
In this hydraulic analogy, energy is being lost from the water as it
falls. This energy is being delivered somewhere else, as sound,heat, or in other forms. We call this energy absorbed. Thus, thepower absorbed is positive.
Height
Flow direction
Power Directions Assumption #1
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Electrical System
made up of various parts
and componentsComponent
in circuit
which
delivers
positive
power
Electrical power
that is delivered
to the system
Nonelectrical power
that will be converted
to electrical power
p
So, a key assumption is that when we say power delivered, wemean that there is power taken from someplace else, converted
and delivered to the electrical system. This is the how thisapproach gives us direction.
For example, in a battery, this power comes from chemical powerin the battery, and is converted to electrical power.
Remember that energy is conserved, and therefore power will be
conserved as well.
Positive power delivered bysomething means that powerfrom somewhere else enters
the electrical system aselectrical power, through thatsomething. In this diagram,the red power (nonelectrical)is being changed to the bluepower (electrical).
Power Directions Assumption #2
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Electrical System
made up of various parts
and components
Component
in circuit
which
absorbs
positive
power
Electrical power
that is absorbed
out of the system
Nonelectrical power
that was converted
from electrical power
p
So, a key assumption is that when we say power absorbed, we
mean that there is power from the electrical system that isconverted to nonelectrical power. This is the how this approachgives us direction.
For example, in a lightbulb, the electrical power is converted tolight and heat (nonelectrical power).
Remember that energy is conserved, and therefore power will beconserved as well.
Positive power absorbed bysomething means that powerfrom the electrical system
leaves as nonelectrical power,through that something. Inthis diagram, the blue power(electrical) is being changedto the red power(nonelectrical).
Power Directions Terminology
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Power Directions Terminology
Synonyms
There are a number of terms that are synonyms for powerabsorbed. We may use:
Power absorbed by Power consumed by Power delivered to Power provided to Power supplied to Power dissipated byThere are a number of terms that are synonyms for power
delivered. We may use: Power delivered by Power provided by Power supplied by
Electrical System
made up of various parts
and components
Component
in circuitwhich
absorbs
positive
power
Electrical power
that is absorbed
out of the system
Nonelectrical power
that was converted
from electrical power
Electrical System
made up of various parts
and components
Component
in circuit
which
delivers
positive
power
Electrical power
that is delivered
to the system
Nonelectrical power
that will be converted
to electrical power
Another Hydraulic Analogy
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ot e yd au c a ogy
Another useful hydraulic analogy that can be used to help
us understand this is presented by A. Bruce Carlson in histextbook, Circuits, published by Brooks/Cole. Thediagram, Figure 1.9, from page 11 of that textbook, isduplicated here.
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Another Hydraulic Analogy Details In this analogy, the electrical circuit is shown at the
left, and the hydraulic analog on the right. As Carlson puts it, The pump (source) forces water
flow (current) through pipes (wires) to drive theturbine (load). The water pressure (potential) ishigher at the inlet port of the turbine than at theoutlet.
Note that the Source isgiven with referencepolarities in the activeconvention, and the Load
with reference polarities inthe passive convention. Asa result, in this case, sinceall quantities are positive,the Source delivers power,and the Load absorbs
power.
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Another Point on Terminology
We always need to be careful of our context.When we say things like the Source deliverspower, we implicitly mean the Source
delivers positive power.Note that the Source isgiven with referencepolarities in the activeconvention, and the Loadwith reference polarities inthe passive convention. Asa result, in this case, sinceall quantities are positive,the Source delivers power,and the Load absorbspower.
Another Point on Terminology
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At the same time, it is also acceptable to write
expressions such as pABS.BY.SOURCE=-5000[W]. This isthe same thing as saying that the power delivered is5000[W].
However, unless the context is clear, it is ambiguous tojust write p =5000[W]. Your answer must be clear,because the direction is important!
Note that the Source isgiven with referencepolarities in the activeconvention, and the Load
with reference polarities inthe passive convention. Asa result, in this case, sinceall quantities are positive,the Source delivers power,and the Load absorbs
power.
Why bother with Sign Conventions?
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Why bother with Sign Conventions?
Students who are new to circuits often questionwhether sign conventions are intended just to makesomething easy seem complicated. It is not so;using sign conventions helps.
The key is that often the direction that power ismoving is not known until later. We want to be ableto write expressions now that will be valid no matterwhat the actual polarities turn out to be.
To do this, we use sign conventions, and the actualdirections come out later whenwe plug values in.
O i f hi P
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Overview of this Part
In this part of the module, we will cover thefollowing topics:
Definitions of energy and power
Sign Conventions for power direction
Which way do the energy and power go?
Hydraulic analogy to energy and power, and
yet another hydraulic analogy