1. ENGS2613 Intro Electrical Science Week 4 Dr. George Scheets
Read 3.3 – 3.4, 4.1 – 4.3
Problems 2.28, 36; 3.6, 13, 17, & 20
Quiz #3, 10 February: Analyze a Circuit
Quiz 2 Results Hi = 10, Low = 1, Average = 5.32, Deviation = 1.80
Quiz A scores bumped by +1

2. Quiz #3 Next Time Closed Book & Neighbor
Up to 3 unattached sheets of notes OK Keep on your desk Have them on hand before you start
Calculator OK
Smart Phones NOT OK
Reaching down for something in backpack?
Get permission first
All we're doing Friday

3. TA Error Report
4 V + -
?? V
30 Ω
4 V + -
?? V
-26 V
4 V
-30 V
1 A

4. Siemen Named after Werner von Siemens 1816 - 1892 German Inventor
1847 Founded what has become Siemens AG
One of largest electro- technical companies in world
Source: Wikipedia

5. DC Circuit with Resistors
R's in Series?
R's in Parallel?
Voltage Divider Circuit?
Current Divider Circuit?
Pause. Look at circuit.
Mark known voltages
Mark known currents
Is it possible to simplify? Worth doing so?
Can you use Ohm's Law?
Have 2 of 3 (ΔV, I, or R)?
Can you use KCL?
Know I's thru a node, except one?
Formally use KCL or KVL
KCL: Write current equations based on Node Current I/O
KVL: Write voltage add/drop equations (ΔV's) based on Current Loops

6. Quiz #3 Resorting to Step 4? If using KCL Node Equations…
Let Grader Know KCL or KVL
If using KCL Node Equations…
Show current directions on each branch
Show voltage drop (+ & - side) across element
If using KVL Loop Equations…
Show current loop direction
Show voltage drop (+ & - side) across element due to each loop
Technique to Use Never Specified

7. 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

8. … Resistors in Parallel = R1 R2 Rn Requivalent
Same nodes on both ends
Two resistors in parallel? Requivalent = (R1*R2)/(R1 + R2) V1 R1 R2 Rn … =
Requivalent V2
1/Requivalent = 1/R1 + 1/R2 + … +1/Rn

9. Voltage Divider Circuit
Resistors in series?
Voltage across series resistors known?
Voltage drop across resistor Rx = V(Rx) (R1+R2+R3) R1 R2 R3 I V

10. Current Divider Circuit
Resistors in parallel
I, R1 – Rn known R1 R2 Rn … V1 V2 I
Ix = I(Requivalent /Rx) if n resistors in ||
I1 = I[R2/(R1+R2)] if 2 resistors in ||

11. 9 volt battery Has an internal resistance of ≈ 2 Ω
When new
Internal resistance ↑ as battery is used
Max current draw (terminals shorted) ≈ 4.5 amps
600 mAh = 24 hours
25 mA
Source: &
& data.energizer.com/PDFs/522.pdf