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ENGS2613 Intro Electrical Science Week & 25 January 2017 Dr

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Presentation on theme: "ENGS2613 Intro Electrical Science Week & 25 January 2017 Dr"— Presentation transcript:

1 ENGS2613 Intro Electrical Science Week 2. 23 & 25 January 2017 Dr
ENGS2613 Intro Electrical Science Week & 25 January 2017 Dr. George Scheets Read 2.1 – 2.5 Problems 1.15, 16, & 29; 2.1, 12, & 16 Quiz #1, 27 January Solve I's, V's, P's given a circuit See Fall 2016 Quiz #1 Yours will be ≈ 20% easier

2 Quiz #1 Closed Book & Neighbor
Up to 3 unattached sheets of notes OK Keep on your desk Calculator OK- No Sharing Smart Phones NOT OK Reaching down for something in backpack? Get permission first

3

4 Wires Generally Have Resistance
12 gauge copper wire (diameter = inches) R ≈ Ω/foot Exception: Superconducting wires have R ≈ 0 Can carry very large currents 77 K = -321◦ F Sources: &

5 Circuit Elements as of 23 January
Active Devices (Ideal. Can generate power) Current flow is Hi → Lo V outside device Independent Voltage Source Independent Current Source Dependent Voltage Source Dependent Current Source Passive Device (can't generate power) Current flow is Hi → Lo V inside device Resistor (Resists current flow) Wire

6 Standard Assumptions Sustained current requires a loop
Path from High to Low voltage side of source Connecting wires have R = 0 Ω No voltage drop regardless of current Treat ground as = 0 volts Ohm's Law: V = IR Voltage drop across device = (Current thru it)(Resistance) Power: P = VI

7 Simple Circuits No current loop exists. Hence no current flows.
V+ 40 Ω 50 Ω 9 V V2 V- = 0 Volts = 0 Volts 9 V V+ 40 Ω 50 Ω V2 = 9 Volts + - + = 0 Volts = 9 Volts - V- = 9 Volts No current loop exists. Hence no current flows. Using V = IR…

8 Resistors in Series I + - + - R1 R2 I + - R = R1 + R2
Exact same current flows thru R1 & R2? Yes? R = R1 + R2 I + - + - R1 R2 I + - R = R1 + R2

9 Electrocution & You Current is the killer 120 VAC
Dangerous if you're wet Image Source:

10 Current Amounts Source: hypertextbook.com/facts/2000/JackHsu.shtml
Source:

11 Hand-to-Hand Resistance, Dry
1.228 MΩ I = V/R = 120 VAC 1,228,000 = μ amps AC = m amps AC = amps AC ≈ amps AC You'll Feel This

12 Hand-to-Hand Resistance, Wet
522 KΩ I = V/R = 120 VAC ,000 = μ amps AC = m amps AC ≈ amps AC You'll Feel This

13 Hand-to-Hand Resistance, Wet & Salty
213 KΩ I = V/R = 120 VAC ,000 = μ amps AC = m amps AC You'll Feel This

14 120 V AC Respect It! Full Body Immersion in Water Can Be Deadly
For Example: Today.Com

15 Current Amounts Those in the water were here.
Source: hypertextbook.com/facts/2000/JackHsu.shtml Source:

16 Residential Areas 240 V AC to House Insulated Lines
120 V AC Neutral 120 V AC Top Wire Not Insulated Sine Wave ≈ 13,200 V AC

17 Hand-to-Hand Resistance, Wet
522 KΩ I = V/R = 13,200 VAC ,000 = 25.3 m amps AC TROUBLE!!

18 Current Amounts Source: hypertextbook.com/facts/2000/JackHsu.shtml
Source:

19 High Voltage Situations
Someone Can't Let Go? Do NOT grab them to pull away Ranked Options Kill Power Pry Them Off Non-metallic Tool Knock Them Off More Dangerous

20 High Voltage Situations
In a Car under fallen Power Lines? Stay There! Car sits on 4 rubber insulators Have to get out? Do NOT step out Do Not simultaneously touch Car & Ground or (Power Line & Ground) Leap Out Still May Kill You if Ground is Wet

21 Lightning 30,000 amps & 15 Coulombs → 500 μsec 120,000 amps & 350 Coulombs → 2.9 msec Human Struck? 10% - 25% Death Rate Source: Wikipedia

22 Kirchhoff's Laws Named after Gustav Kirchhoff 1824 - 1887
Prussian Physicist University Professor 1845: Developed His Laws While a Student Became his PhD dissertation Source: Wikipedia

23 Node generally = Wire Current going in = Current going out
Kirchoff's Current Law Plumbing System Electrical System α Gps α A 3 Gps 3 A β Gps β A α + β Must = 3 α + β Must = 3 Node generally = Wire Current going in = Current going out

24 Kirchoff's Voltage Law Electrical System CW KVL Loop Plumbing System
+ 6 PSI + 50 Ω 9 V - 4 V + - 40 Ω 3 PSI Pump - 0 Volts 1 PSI Electrical System CW KVL Loop = 0 CCW KVL Loop – 9 = 0 Plumbing System +5 – 3 – 2 = 0 psi

25 DC Circuit with Resistors
To Solve, Need… Ohm's Law Kirchhoff's Current Law Kirchhoff's Voltage Law … Properly Applied Algebra

26 Using Kirchhoff's Voltage Law
Draw current loops Arbitrary direction (clockwise or counter-clockwise) Hit each circuit element at least once (preferably only once) Label voltage drops for each element MUST follow current directions Passive device (Resistor): Current into + side, Current out on – side Active device (Voltage or Current Source): Current exits + side, Current enters – side + side is at a higher voltage than – side (if current direction is correct) Write equation for voltage drops or gains around loop Arbitrary direction (with or against current flow) Going from – side to + side? Positive value in equation Going from + side to – side? Negative value in equation Solve Equations

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