1. ENGS2613 Intro Electrical Science Week 5
Read 4.4 – 4.8
Problems 3.30; 4.3, 6, 7, 17, & 22
Exam #1, Friday, Chapters 1.1 – 4.8 < Source Transformations
HKN Review, Thursday, 7:00 pm, PS141
Quiz 3 Results Hi = 10, Low = 2, Ave = 6.81, Deviation = 1.82

2. Exam #1 Friday 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
Budget your time!

3. A Possible Exam Technique
4 pages, 50 minutes
1st Pass
Allocate 10 minutes a page
Not done after 10? Move on.
2nd Pass
Have at least 9-10 minutes left
Seen all problems
Should know where it's cost-effective to go
Don't get sucked into a single page!!!

4. 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

5. What are you Comfortable With?
KVL? ΔVoltage & Loop Currents Use it on everything
KCL? Current I/O at Nodes Use it on everything
Both? One might be easier to use

6. Some Terminology ne: Number of Essential Nodes
Essential Node = Node with > 2 elements attached
be: Number of Essential Branches
Path from 1 Essential Node to another…
…that doesn't pass thru another Essential Node…
…and has Unknown Current
Mesh
Loop that does not Enclose any other Loop
Nodal Analysis (KCL) a.k.a. Node Voltage Method
Requires ne – 1 equations
Mesh Current Analaysis (KVL)
Requires be – (ne – 1) # equations
Frequently this = # Enclosed Regions

7. Node Voltage Method (KCL)
Identify Essential Nodes
If necessary, make one ground
Define Essential Node voltages
If voltage known, write # value. If unknown, assign label.
Draw & label currents in/out of each node. Mark voltage drops accordingly (+ & -)
Apply KCL at each Essential Node (except ground) Generally ne -1 equations
Solve

8. Mesh Current Method (KVL)
Draw [be – (ne – 1)] Current Loops
Frequently this = Number of Enclosed Regions
Label Voltage Drop or Increase (+ or -)
Caused by each loop
Have a current source?
Note Δvoltage across, if known. Otherwise assign a label (such as V1 = voltage across source).
Write KVL around each loop
Solve

9. Planar Circuit
Figure 4.2 in the text shows an example of a non-planar circuit.
Source: Our textbook

10. Some Exceptions Node Voltage Method (KCL) Exception
Generally requires (ne – 1) KCL equations
Exception
Voltage Source only element between 2 Essential Nodes?
Number of KCL equations can be reduced
See Section 4.4 for details
Mesh Current Method
Generally requires [be – (ne – 1)] Loops Usually this = Number of Enclosed Regions
Branch includes a Current Source?
Number of KVL equations can be reduced
See Section 4.7 for details

11. Source TransformationVs R + - Is R ↑ =
These circuits are functionally the same if Vs = Is R

12. Source Transformation Possible on 9 A & 8 Ω elements?
Vout
10 V + -
9 A ↑
8 Ω
16 Ω
Vout
10 V + -
9 A ↑
16 Ω
8 Ω

13. Source Transformation Possible on 9 A & 8 Ω elements?
5 Ω
Vout - ↑
10 V
9 A
16 Ω
8 Ω +
Vout
10 V + -
72 V
16 Ω
8 Ω
5 Ω

14. Thevenin Equivalent Circuit
Named after Leon Charles Thevenin
1857 – 1926
French Telegraph Engineer
1880's Investigated Complex Electrical Circuits
Source: Wikipedia