Networks I for M.E.
ECE 09.201 - 2
James K. Beard, Ph.D.
Rowan Hall 238A
beard@rowan.edu
http://rowan.jkbeard.com
September 11, 2006
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
+
vab
-
-
vba
+
a
September 11, 2006
vab  vba
b
Networks I for M.E.
Slide 2
Power


Power is the time rate of expending energy.
Power absorbed by an element is positive,
Power delivered by an element is negative.
i
a
b
+
vab
-
-
vba
+
i
a
September 11, 2006
dw dw dq
p


vi
dt dq dt
b
Networks I for M.E.
Slide 3
Learning Check #6

If 6V (volts) is dissipated across a resistor
in which the current is 2A (amperes) what
is the power used in watts?
September 11, 2006
Networks I for M.E.
Slide 4
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?
September 11, 2006
Networks I for M.E.
Slide 5
Learning Check #7

PSC: positive current flows from
positive voltage to negative voltage.
+
vab
-
i
a
b
i
a
vab
+
b
If i is positive, does
If i is positive, does
this conform with PSC?
this conform with PSC?
September 11, 2006
Networks I for M.E.
Slide 6
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?
September 11, 2006
Networks I for M.E.
Slide 7
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
- vab (source)
+
i
a
b
September 11, 2006
Networks I for M.E.
Slide 8
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.

September 11, 2006
Networks I for M.E.
Slide 9
Power and PSC Quiz

What is the power absorbed or
supplied by the element below, when i =
-2A?
-
i
a
vab = 12V +
b
Power = -12V x -2A = 24 W
 Does adhere to passive sign
convention, so power is absorbed.

September 11, 2006
Networks I for M.E.
Slide 10
Power and Energy
p=v•i
power = voltage * current (units = watts)
power is the time rate of expending energy
t
w   pdt
0
energy = power * time (units = Joules [w-s])
Energy is the capacity to do work
September 11, 2006
Networks I for M.E.
Slide 11
Power and Energy

energy = force x distance

power = energy / time period (secs)
September 11, 2006
Networks I for M.E.
Slide 12
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
September 11, 2006
Networks I for M.E.
Slide 13
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?
September 11, 2006
Networks I for M.E.
Slide 14
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
September 11, 2006
Networks I for M.E.
Slide 15
Learning Check #8

Your iPod shuffle uses a small 3.7V
polymer lithium battery with stored energy
of 11,322 joules. How many hours will it
play tunes if it draws 70.81mA current
when in operation?
September 11, 2006
Networks I for M.E.
Slide 16
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
September 11, 2006
vab -
b
Networks I for M.E.
Slide 17
Voltmeters and Ammeters


Current measurements require breaking into
the circuit so the ammeter is in series with the
current flow (or an expensive inductive
pickup)
Made with red probe (+) at point b, and black
probe (-) at point c
+
i
a
September 11, 2006
vab bc
Networks I for M.E.
Slide 18
Ideal Meters


Ammeters – negligible voltage drop
through it
Voltmeters – negligible current flows into it
September 11, 2006
Networks I for M.E.
Slide 19
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)





Problem statement
Situation and assumptions
Goal and requirements
Plan  act  verify  if correct, solved
If not, plan  act  verify  iterate as needed
September 11, 2006
Networks I for M.E.
Slide 20
Homework for next Tuesday




See next slide for Assignment #1
Show all work for any credit
Dorf & Svoboda, pp. 16-18, pp. 44-45
Begin Lab HW Assignment 1
September 11, 2006
Networks I for M.E.
Slide 21
Assignment 1

Due Tuesday, September 19, 8:00 AM
 Dorf

& Svoboda, pp. 16-18
Problems
1.2-1, -4, -6
 1.5-2, -3, -8
 1.7-1

 Dorf

& Svoboda, pp. 44-45
Problems
2.2-1, -2, -4
 2.4-1, -2, -3, -5

NOTE: Show ALL WORK for credit
September 11, 2006
Networks I for M.E.
Slide 22
Lab Homework Assignment 1







Due Monday, September 11, 12:15 PM
Lab report due Monday, September 18, 12:15 PM
Complete all four (4) MentorGraphics tutorials linked to
http://users.rowan.edu/~jansson/autumn06/Networks1/tutorial.html
In the last tutorial (Accusim) you will generate a DC Power Report
for the circuit you build and saved in the Design Architect tutorial.
Print out this DC Power Report and turn it in at the beginning of the
next lab meeting on September 11.
Show that you personally have completed each step by the
appropriate number of “Snapshot” pictures added to your report.
Complete the Matlab tutorial linked to the same page and include at
least three (3) screen snapshots to show that you completed the
work.
Log on using your Elvis Account
For assistance please see Mr. Al Capuano (capuano@rowan.edu)
September 11, 2006
Networks I for M.E.
Slide 23