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ELECTRIC CIRCUITS (E 250) LECTURE NOTES

(ALEXANDER & SADIKU TEXT)

*************** WEEK 1 ***************

1 BASIC CONCEPTS

Per Alexander – 3 parts (more than enough for 2 semester course) Part 1 – CH 1 – 8 Part 2 – Ch 9 – 14

Part 3 – 15 – 19 (19 total chapters)

I. Introduction (Ch. 1.1 - Alexander) & CT Preliminaries

A. CT Preliminaries 1. Hand out syllabus, adds (add log, add NOW), sign-in sheet, photo 2. What are we going to learn in this course?

a. Fundamentals of circuit analysis b. Basic circuit theorems c. RL, RC, RLC circuits d. Sinusoids and phasors e. Steady state analysis f. Polyphase circuits g. Diodes, transistors (maybe)

3. Syllabus – go over it 4. Hints on how to be a good student

a. Be ON TOP OF STUFF! b. Come to class, get & read the book, do ALL of hw (on time, or even early!) c. Be prepared for lecture – read about the topic beforehand d. Check your email, Bb, & the website e. STUDY – 3 hours of work for each hour of lecture per week (for STEM majors) f. Be ACTIVE in lecture – take notes, ask questions, participate in lecture! g. Don’t fall behind!

5. Learn to take notes a. Write everything the professor writes b. Sometimes write what the prof SAYS (tough one!) c. Develop your own shorthand (abbreviate) d. “A decrease in speed of 10 percent results in approximately a 19 percent decrease in

wind drag” (in your notes, write as: “10% speed ~19% wind drag”) e. Approximately = “~”, increase = , decrease = , “results in…” = .

6. Introductions a. Me – mechanical engineering (robotics), industry, academia b. You – name, why taking class, area of interest

B. Electric circuit theory & electromagnetic theory basis for all branches of EE

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C. Branches of EE: power, electric machines, control, electronics, communications, instrumentation.

D. Electric circuit – an interconnection of electrical elements

+

E. History of Electricity 1. 600 BC – amber can be charged by rubbing 2. 1600 AD – English scientist William Gilbert describes the “electrification” of many

substances & coins term “electricity” (Greek: “amber”) 3. 1700s – Benjamin Franklin and his famous kite experiment

F. Atomic structure

electrons () charge(1836x less massive)

protons (+) charge

neutrons (0) charge

metals

want to loseelectrons

want to gainelectrons

noble gases

B

Si

Ge

TeSb

As

AlZn

Sn

PbHg

Fe Ni Cu

heavier

lighter

Periodic Table of Elements G. Charge

1. Simple rules

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++

+

Like charges repel each other. Unlike charges attract each other.

2. Net atomic charge – count protons & electrons (proton = +1; e- = – 1) 3. So atom with equal # of protons & e- has net atomic charge = zero. 4. Ions – atoms can gain & lose electrons.

a. ( + ) ion – atom with lost electron b. ( – ) ion – atom with gained electron

H. Metals & delocalization of electrons

1. Electrons move in orbitals (some closer to nucleus, some farther), ea with specific # of spaces, & energy level (1s2, 2s2, 2p6; 2, 8, 18, 32)

2. Valence electrons – outermost electrons, & the most likely to be lost. 3. Atoms “prefer” full orbitals. 4. Heavier elements (lower on Periodic table) have more of e-. 5. Elements on LEFT tend to have extra e- that they want to get rid of. 6. Meet both criteria – they are heavy and have extra e-. 7. Have many loosely held electrons.

8. Seen as lattice of positive ions (cations) in a sea of delocalized electrons.

++

+

++

9. Bottom line – many metals are good conductors of electric charge. Copper has 4 major shells (having 2, 8, 18, and 1 electron each). The last e- is loosely held by the nucleus (Cu wants FULL orbitals). At room T, there is plenty of E to ionize Cu atom, so many “free electrons”.

II. System of units (1.2 Alexander) & Technical notation

A. SI (metric) 1. Length (meter) 2. mass (kg) 3. Time (s) 4. Current (A) 5. Temperature (K) 6. Luminous intensity (candela = cd)

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B. Powers of 10 1. 10-1 = 0.1 2. 10-2 = 0.02 3. 1000 m = 1.000 x 103 m = 1,000,000 mm

C. SI Prefixes (customary to use powers of 3)

1. 101 = deka (da) 10-1 = deci (d) 2. 102 = hecto (h) 10-2 = centi (c) 3. 103 = kilo (k) 10-3 = milli (m) 4. 106 = Mega, (M) 10-6 = micro () 5. 109 = Giga (G) 10-9 = nano (n) 6. 1012 = Tera (T) 10-12 = pico (p) 7. 1015 = Peta (P) 10-15 = femto (f) 8. 1018 = Exa (E) 10-18 = atto (a)

D. So, .00000533 Farads = 5.33 F E. Engineering notation (a x 10b)

1. a between 1 & 1000, and b is a multiple of 3

III. Charge & Current (1.3 Alexander)

A. Charge 1. An electrical property of atomic particles, measured in Coulombs

Coulomb1 charge of 181024.6 electrons

Thus, one electron has charge

Ce 19

18

1 10602.11024.6

11

which is the smallest possible quantity of charge

2. Charge conserved (neither created nor destroyed) 3. Electrostatic fields – region near a charged body in which force is applied to charged

bodies.

+-

B. Battery with wire

1. Battery – has an imbalance of charge (excess e on 1 end, excess (+) charge on other). These charges were separated using work.

2. Wire – made of atoms with plenty of free e-. 3. Imbalance pushes the free e- in the wire.

a. Like charges repel – unlike charge attract.

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b. Coulomb’s Law – force of attraction

2

21

r

qqkF e

where

22

9109Cm

Nxke

4. Flow of charge – think of musical chairs

+

+

electrons

current