Electric Circuit Variables

1
Electric Circuit Variables

• NETWORKS 1 ECE 09.201.02
• 09/04/07 Lecture 1
• ROWAN UNIVERSITY
• College of Engineering
• Prof. John Colton
• DEPARTMENT OF ELECTRICAL COMPUTER ENGINEERING
• Fall 2007 - Quarter One

2
Welcome to Networks I

• Course Learning Objectives
• Define circuit variables and elements
• Master Ohms Law, Kirchoffs Laws, etc.
• Analyze electrical circuits
• Apply circuit parameters (v, i, p, etc.)
• Analyze DC circuits with passive elements
  including resistance, energy storage (C,L)
• Analyze op amp circuits
• Build and Model circuits using Mentor Graphics
  and MATLAB

3
Course Potpourri

• Lectures M/T 800 AM-915 AM Rowan 239
• Laboratories M 1215 PM-300 PM Rowan 204/6, 221
• Required Text Introduction to Electric
  Circuits, Dorf and Svoboda,
• 7th Edition 2006
• Syllabus/Text (read ahead Chapters 1/2)
• Problem Sets (issued on each Tuesday, due 800
  AM the next
• Monday no credit for late problem sets
  show all work for credit)
• Labs (labs conducted each Monday, reports due
  1215 PM the next
• Monday no credit for late lab reports)
• Website users.rowan.edu/colton/fall07/networksI
  /index.html
• Course announcements made in class
• Email check regularly (daily)

4
Learning Evaluation

• Grading Policy
• 3 Tests 60 (3X20)
• Assignments (40)
• Problem Sets (15)
• Lab reports, participation, homework (15)
• In-Class Participation (10)

5
Networks I Labs

• Lab Groups 31 students, 10 WS 9 groups of 3,
  1 group of 4
• Email your lab group to me by Monday 09/10
• Lab group pictures taken during 09/10 lab period
• Logging on to Mentor Graphics and MATLAB see
  website
• Labs start 1200 noon 1215 PM and end 300 PM
  be efficient
• Attendance and punctuality are mandatory
• Labs are standalone not synchronized with
  lectures read ahead
• Student tool kit see website
• Do lab homework prior to lab to hand in at
  beginning of lab period
• Read and understand lab project before the lab
  starts
• Lab reports due at beginning of next lab late
  reports not accepted
• Laboratory Report Format see website
• Lab Report Grading see website for Guidelines

6
09/10 Networks I Lab

• General Lab Procedures 20 min
• Mentor Demonstration 30 min
• Mentor Tutorials Run-through, 115 min
• including DC Circuit Project

7
Electric Circuit Variables Topics

• Historical perspective
• Electric circuits and current
• Systems of units
• Voltage
• Power and energy
• Measurement voltmeters and ammeters
• Circuit analysis and design

8
Imagine a World with..

• No Internet
• No cell phones
• No computers
• No television or video games
• No mass communication
• No tall buildings

9
Imagine a World with..

• No electricity
• No electronic devices
• No medical technology
• No appliances
• Refrigerators
• Microwaves
• Water heaters
• Air conditioning
• No traffic controls

10
That world would be

• Primitive
• A very hard life for human beings
• Difficult for human survival on todays
  population scale

11
Historical Perspective

• 13.7B BC Big Bang
• 13.4B Stars and galaxies form
• 5B Birth of our sun
• 3.8B Early life begins
• 700M First animals
• 200M Mammals evolve
• 65M Dinosaurs extinct
• 600K Homo sapiens evolve
• 600 AD Attractive power of ES materials
• 1551 Electricity and magnetism defined
• 1746 Atmospheric electricity discovered
• 1814 Electrical Spectrum detailed

12
Electrical Technology Emerges Relatively Recently

• 1821 First Electric Motor
• 1825 First Electromagnet
• 1832 First E-M Induction Generator
• 1837 Telegraph
• 1879 First DC Power System
• 1888 First AC Generator
• 1895 X-rays Discovered
• 1901 Radio

13
Quotable Quotes

• Take warning! Alternating currents are
  dangerous! They are fit only for powering the
  electric chair. The only similarity between an AC
  and a DC lighting system is that they both start
  from the same coal pile.
• Thomas Edison Pamphlet of 1887
• Heavier than air flying machines are impossible
• Lord Kelvin Royal Society 1895
• There is no likelihood man can ever tap the
  power of the atom
• Robert Milliken Nobel Laureate Physics 1923

14
20th Century Discovery

• AC Electric Grids - 1900s
• Fluorescent Lighting - 1930s
• Computing 1930s
• Television 1940s
• Personal Computing - 1970s
• Internet 1990
• 21st Century ?

15
Electric Circuits Current Flow

• An electric circuit is an interconnection of
  circuit elements linked together to form a closed
  path, so that electric current may flow
  continuously

i1
Resistor
Battery
Where is ground in this circuit?
16
Electric Circuits Current Flow

• An electric circuit is an interconnection of
  circuit elements linked together to form a closed
  path, so that electric current may flow
  continuously

i1
Resistor
Battery
17
Electric Circuits Current Flow

• An electric circuit is an interconnection of
  circuit elements linked together to form a closed
  path, so that electric current may flow
  continuously

i1
Resistor
Battery
18
Current flow defined

• 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

i1
i2
19
Learning Check charge and current
Assuming q(t) 0 for t lt 0, how much charge
enters the element in 2 seconds if the current
entering the element is as pictured?
20
Learning Check charge and current
Assuming q(t) 0 for t lt 0, how much charge
enters the element in 2 seconds if the current
entering the element is as pictured?

1 1.5 2.5 coulombs
q
21
Units

• Systeme International dUnites
• Base Units (m, kg, s, A, K, mol, cd)
• Derived Units (J, W, C, V, O, S, F, Wb, H)
• What are base units for Energy (J) and Power (W)?

22
Voltage

• The voltage across an element is the work
  (energy) required to move a unit positive charge
  from the - terminal to the terminal.

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Power

• Power is the time rate of expending energy
• Power can be absorbed (dissipated) by an element
• Power can be delivered (supplied) by an element

dq
dw



dt
dq
24
Learning Check power

• If 6V (volts) is dissipated across a resistor in
  which the current is 2A (amperes) what is the
  power used in watts?

25
Learning Check power

• If 6V (volts) is dissipated across a resistor in
  which the current is 2A (amperes) what is the
  power used in watts?

26
Passive Sign Convention (PSC)

• Positive current flows from positive voltage to
  negative voltage.

Positive current into a positive terminal means
power is dissipated
Positive current into a negative terminal means
power is supplied
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Power and PSC

• p v i
• Power is absorbed by an element adhering to the
  Passive Sign Convention (sink)
• Power is supplied by an element not adhering to
  the passive sign convention (source)

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Example Power and PSC

• What is the power absorbed or supplied by the
  element below, when i 4A?

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Example Power and PSC

• What is the power absorbed or supplied by the
  element below, when i 4A?
• p 12V x 4A 48 W
• adheres to passive sign convention, so power is
  dissipated.

30
Example Power and PSC

• What is the power absorbed or supplied by the
  element below, when i 4A?

31
Example Power and PSC

• What is the power absorbed or supplied by the
  element below, when i 4A?
• p 12V x 4A 48 W
• does not adhere to passive sign convention,
• so power is supplied.

32
Example power and PSC

• What is the power absorbed or supplied by the
  element below, when i -2A?

33
Example power and PSC

• What is the power absorbed or supplied by the
  element below, when i -2A?
• p 12V x 2A 24 W
• adheres to passive sign convention, so power is
  dissipated.

34
Power and energy

• energy force (n) x distance (m)
• power energy (J) / time period (s)

35
Example Power and energy

• 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.

36
Example Power and energy

• 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 30 J
• power energy / second (J/secWatts)
• power 30J/10-2 sec 3000W 3kW

37
Electrical power and energy

• p v i
• power voltage current (units Watts)
• power is the time rate of expending energy
• energy power time (units Joules W
  s)
• energy is the capacity to do work

38
Example Power and energy

• 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?

39
Example Power and energy

• 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?

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
40
Example Power and energy

• 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?

41
Example Power and energy

• 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?
• Answer about 12 hours

42
Electrical Measurements

• I often say that when you can measure what you
  are speaking about and express it in numbers, you
  know something about it but when you cannot
  measure it or express it in numbers, your
  knowledge is of a meager and unsatisfactory kind
  it may be the beginning of knowledge, but you
  have scarcely, in your thoughts, advanced to the
  stage of a science, whatever the matter may be.
• Lord Kelvin, 1883

43
Voltmeters

• Voltage measurements are made with (analog or
  digital type) voltmeters
• Voltage measurements are made with the voltmeter
  red probe () at point a, and black probe (-) at
  point b

44
Ammeters

• Current measurements require breaking into the
  circuit so the ammeter is in series with the
  current flow
• Current measurements made with the ammeter red
  probe () at point b, and black probe (-) at
  point c

45
Ideal meters

• Ammeter negligible voltage drop through it
• Voltmeter negligible current flows into it

46
Circuit analysis

• Circuit Analysis is concerned with the
  methodological study of a circuit to determine
  direction and magnitude of one or more circuit
  variables (v, a, p, )
• Problem statement
• Situation and assumptions
• Goal and requirements
• Plan ? act ? verify ? if correct, solved
• If not, plan ? act ? verify ? iterate as needed

47
Homework for next week

• See website for Problem Set 1
• Problems Chapters 1 and 2
• Due Monday 09/10 800 AM
• Show all work for any credit
• See website for Lab Homework 1
• Mostly reading Mentor tutorials
• DC Circuit example worked report to be turned
  in
• Dont have to read MATLAB tutorial yet
• Report due Monday 09/17 1215 PM
• Read and understand Lab Project 1

48
Problem Set 1

• Dorf and Svoboda pp 16-18
• 1.2-4, 1.2-5
• 1.3-2
• 1.5-2, 1.5-3, 1.5-6, 1.5-7, 1.5-8
• Dorf and Svoboda pp 44-52
• 2.2-1, 2.2-4