Download ppt

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
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
TA Error Report
4V
+
?? V
4V
-
-26 V
+
?? V
4V
1A
-30 V
30 Ω
Siemen
Named after Werner von Siemens
1816 - 1892
 German Inventor
 1847
Founded what has
become Siemens AG

 One
of largest electrotechnical companies in
world
Source: Wikipedia
DC Circuit with Resistors
R's in Series?
 Pause. Look at circuit.
R's in Parallel?
 Mark known voltages
Voltage Divider Circuit?
Current Divider Circuit?
 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
Quiz #3

Resorting to Step 4?
 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
Resistors in Series

Exact same current flows thru R1 & R2?
Yes? R = R1 + R2
I
+
- +
-
R1
+
R2
-
R = R1 + R2
I
Resistors in Parallel
Same nodes on both ends
V1

R1
R2
…
Rn
=
V2
1/Requivalent = 1/R1 + 1/R2 + … +1/Rn

Two resistors in parallel?
Requivalent = (R1*R2)/(R1 + R2)
Requivalent
Voltage Divider Circuit


Resistors in series?
Voltage across series resistors known?
I
R1
R2
R3
V

Voltage drop across resistor Rx =
V(Rx)
(R1+R2+R3)
Current Divider Circuit


Resistors in
parallel
I, R1 – Rn known
R1
I
R2
V1
…
V2
Ix = I(Requivalent /Rx) if n resistors in ||
I1 = I[R2/(R1+R2)] if 2 resistors in ||
Rn
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: www.izapmen.com & www.learningaboutelectronics.com/Articles/Battery-internal-resistance
& data.energizer.com/PDFs/522.pdf