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ENGS2613 Intro Electrical Science
Week 3
Dr. George Scheets
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Read
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Problems
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2.17, 20, 22, 23, 26, & 27
Quiz #2, 3 February
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2.5, 3.1, & 3.2
Analyze a circuit using either KVL or KCL equations
Quiz #1 Available for pickup in ES016
Quiz 1A Scores have been bumped by 1 point
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Up to a max score of 10
Using Kirchhoff's Current Law
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Draw & label current thru every element
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Label voltage drops for each element
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Node = wire at single voltage. Boundary is set by any circuit element.
Write Current Equations, mostly using KCL & Ohm's Law
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Passive device (Resistor):
 MUST follow current directions
 Current into + voltage side, Current out on – voltage side
Active device (Voltage or Current source):
 Generally Assume Current exits + side & enters – side
Label voltages at each node
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Arbitrary direction
Hit each circuit element once (& only once)
Same current? Use same label
KCL: Sum of currents entering node = sum of currents exiting
Solve Equations
DC Circuit with Resistors
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Pause. Look at circuit.
 Mark
known voltages
 Mark known currents
 Is it possible to simplify? Worth doing so?
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Can you use Ohm's Law?
 Have
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2 of 3 (V, I, or R)?
Can you use KCL?
 Know
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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
Noted Problem Areas
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Ohm's Law: V = IR
 Voltage
Drop across a device =
Current thru the device * Device's Resistance
 Might Help to think of it as ΔV = IR
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KVL Loop Currents
=
Actual current thru a device if only 1 Loop Current
 More than one Loop Current?
Actual current = sum of the Loop Currents
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Power
 Active
device: P = VI
 Passive device (Resistor): P = VI = I2R = V2/R
Transistors
Source: learn.mikroe.com
& hothardware.com

Intel's i7 processor
has over 1.3 billion
transitors.