CHAPTERS 1 & 2
NETWORKS 1:
0909201-01
10 September 2002 – Lecture 1b
ROWAN UNIVERSITY
College of Engineering
Professor Peter Mark Jansson, PP PE
DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING
Autumn Semester 2002
Text is In Bookstore:
Required Text :
 Introduction to Electric Circuits
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5th Edition
Dorf and Svoboda
Assigned Reading per Syllabus
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Chapters 1 & 2
One-Minute Papers -
summary
passive sign convention (3)
little fast, too quickly on slides (2)
energy vs. power (2)
voltage vs. current (defn. & calcs) (2)
voltmeter & ammeter operation (2)
no syllabus?
solving a circuit w/ resistors
unit conversion
remembering the calculus
Networks I
Today’s Learning Objectives –
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Define circuit elements
Analyze electrical circuits
Apply circuit parameters (v, i, r, p, etc.)
Analyze DC circuits with passive elements
including: resistance
chapter 1 – overview
history of electricity - done
electric circuits and current flow
systems of units - done
voltage
power and energy
voltmeters and ammeters
circuit analysis and design
electric circuits & current flow
Current is the time rate of flow of electric
charge (q) past a given point
Use lower case to indicate a time varying
current and upper case to indicate a constant
or direct current
dq
i
dt
i1   i2
i1
i2
voltage
The voltage across an element is the work
(energy) required to move a unit positive
charge from the - terminal to the + terminal.
a
b
dw
v
dq
a
+
vab
-
-
vba
+
vab  vba
b
voltage / current analogy
mechanical system analogy:
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pump, fluid pressure (head), velocity
battery, voltage, current
high pressure (head)  high voltage
increased fluid flow  high current
increasing either: increases power
circuit analogy
envision a closed system of water flowing in
troughs
pumps elevate the head of the flow and
increase its velocity in various troughs
flow of mass is conserved
energy can be added (pumps) or extracted
(waterwheels) though overall system of water
flow is conserved
energy is transferred by head and velocity
in a given part of circuit flowrate is constant
power
Power is the rate of expending energy.
Power absorbed by an element is positive,
Power delivered by an element is negative.
i
a
b
i
a
+
vab
-
-
vba
+
dw dw dq
p


vi
dt dq dt
b
passive sign convention (psc)
positive current flows from positive
voltage to negative voltage.
+
vab
-
i
a
b
i
a
vab
+
b
Is the current in
Is the current in
this resistor positive
this element positive
or negative?
or negative?
power and psc
p=v•i
Power is absorbed by an element adhering to the
passive sign convention (sink)
+ vab i
a
b
Power is supplied by an element not adhering to
the passive sign convention (source)
i
a
vab +
b
power and psc example
what is the power absorbed or supplied by
the element below, when i = 4A?
i
a
vab = 12V +
b
power = 12V x 4A = 48 W
does not adhere to passive sign convention,
so power is supplied.
power and psc quiz
what is the power absorbed or supplied by
the element below, when i = 4A?
i
a
vab = 12V +
b
power = 12V x 4A = 48 W
does not adhere to passive sign convention,
so power is supplied.
power and energy
p=v•i
power = voltage * current
power is the time rate of expending energy

w
0
pdt
t
energy = power * time
energy is the capacity to do work
power and energy
energy = force x distance
power = energy / time period (secs)
power and energy example
a mass of 300 grams experiences a force of
200 newtons. Find the energy (or work
expended) if the mass moves 15 cm. Also
find the power if the move is completed in 10
milliseconds.
energy = force x distance (N • m)
energy = 200 x .15 = 30J
power = energy / second (J/sec=Watts)
power = 30J/10-2 sec = 3000W = 3kW
power and energy quiz
a Motorola StarTAC cellular phone uses
a small 3.6V lithium ion battery with
nominal stored energy of 200 joules.
For how long will it power the phone if
it draws a 3-mA current when in
operation?
quiz solution
200 joules = 200 watt-secs
3.6 V x 3 mA = 1.08 x 10-2 watts
200 watt-secs / 1.08 x 10-2 watts =
18,519 seconds
18,519 seconds / 3600 sec/hr =
5.1 hours
voltmeters and ammeters
dc current and voltage measurements
are made with (analog or digital type)
ammeters and voltmeters
voltage measurements are made with
red probe (+) at point a, and black
probe (-) at point b
+
i
a
vab b
voltmeters and ammeters
current measurements require breaking
into the circuit so the ammeter is in
series with the current flow
made with red probe (+) at point b,
and black probe (-) at point c
+
i
a
vab bc
ideal meters
ammeters – negligible voltage drop
through it
voltmeters – negligible current flows
into it
circuit analysis and design
analysis – concerned with the
methodological study of a circuit to determine
direction and magnitude of one or more
circuit variables (V, A)
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problem statement
situation and assumptions
goal and requirements
plan  act  verify  if correct, solved
if not, plan  act  verify  iterate as needed
chapter 2 - overview
engineering and linear models
active and passive circuit elements
resistors – Ohm’s Law
independent sources
dependent sources
transducers
switches