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MODULE 3: Basic Circuits - Resistance
SUMMER CHALLENGE
Electrical Engineering: Smart Lighting
Michael Rahaim, PhD Candidate
Multimedia Communications Lab
Boston University
[email protected]
Module 3: Basic Circuits
07/08/2015
Overview
Boston
Circuits
Review
University Slideshow Title Goes Here
 Resistance and Resistors
 Ohms Law
 Breadboards
 Capacitance
 Experiments
 Resistive Circuit
 Voltage Divider
 RC Circuit
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Module 3: Basic Circuits
07/08/2015
Recap - What is a Circuit?
Boston
InUniversity
a circuit,
how are the start and end related?
Slideshow Title Goes Here
 They’re the same!
 What happens if there isn’t a continuous path?
 Open Circuit – No flow of charge (or electrons)
 What happens when a conduit connects two points?
 Charge (and electrons) can flow between the points
 Short Circuit – Directly connecting two points of different voltage
 Switch
 Device that can open or close a circuit
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Module 3: Basic Circuits
07/08/2015
Resistance
Boston
AsUniversity
charge
flows from high to low V, energy is released
Slideshow Title Goes Here
 Where does it go??
 As electrons flow, they encounter resistance
 Friction from electrons moving against the resistance generates heat
 Resistance is a function of material, length, and cross-sectional area
 Resistance is measured in Ohms [Ω]
 Wires have resistance, but it is minimal and a direct
connection between different voltage levels is a short
 The filament in an incandescent
light introduces resistance
 The heat energy causes the filament to
“glow” white-hot and produce light
Incandescent
Light
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Module 3: Basic Circuits
07/08/2015
Resistors
Boston University Slideshow Title Goes Here
??
??
??
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Module 3: Basic Circuits
07/08/2015
?? Law
Ohms
 German professor who published a book in 1827
Boston University Slideshow Title Goes Here
that includes what is now known as Ohm's law
𝑉 = 𝐼𝑅
 Ohm's Law: Voltage across a resistor is directly
proportional to the current flowing through it.
+
𝑉 = 𝐼𝑅
-
i𝐼
v
R
-
+
 The proportionality constant is the resistance!
𝑉
𝐼=
𝑅
Georg Simon Ohm
(1789 – 1854)
𝑉
𝑅=
𝐼
 What happens in the case of an open circuit (i.e., 𝑅 ≈ ∞)?
 What happens in the case of a short circuit (i.e., 𝑅 ≈ 0)?
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Module 3: Basic Circuits
07/08/2015
Series vs Parallel
V0  V1  V2  IR1  IR2
 I  R1  R2 
Boston
Series
Resistance
University Slideshow Title Goes Here
I
 IRs
+
+
A
Rs
V
Rs  R1  R2
V2
R2
V0
I
V1
R1
-
 Parallel Resistance I  I  I  V  V  V  1  1   V


1
2
R1 R2
R
R
I
Rp
2 
 1
I
I1
V
R1
I2
R2
V
Rp
1
1
1
 
Rp R1 R2
Rp 
R1 R2
R1  R2
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Module 3: Basic Circuits
07/08/2015
Breadboards
 Why do we use breadboards?
Boston University Slideshow Title Goes Here
 Temporary Circuits
 Prototyping
 No Soldering
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Module 3: Basic Circuits
07/08/2015
Anatomy of a Breadboard
Boston University Slideshow Title Goes Here
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Module 3: Basic Circuits
07/08/2015
Boston University Slideshow Title Goes Here
POSITIVE
NEGATIVE
RESISTOR
LED
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Module 3: Basic Circuits
07/08/2015
SHORT EXERCISE
1. Copy the schematic.
2. Label where each of the
numbers are.
Boston University Slideshow Title Goes Here
1
8
7
6
2
3
4
5
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Module 3: Basic Circuits
07/08/2015
Voltage Divider Circuit
I
Boston University Slideshow Title Goes Here
R1
V1
R2
V2
V0
V0
I

Rs R1  R2
A
V0
R1
Also V1 
V0
 R1  R2 
V0
V2  IR2 
R2
 R1  R2 
R2
V2 
V0
 R1  R2 
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Module 3: Basic Circuits
07/08/2015
Experiment I
Boston
Voltage
Divider
University Slideshow Title Goes Here
 Resistive Circuits
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Module 3: Basic Circuits
07/08/2015
Capacitance
Boston
A University
capacitor
has capacity to store energy in the form of
Slideshow Title Goes Here
electrical charge producing a voltage across plates
 Storage of energy leads to time dependency
 This was NOT the case in purely resistive circuits.
 Capacitance is measured in Farads [𝐹]
𝑖 = Instantaneous Current
d𝑣
𝑖=𝐶
d𝑣
= Instantaneous rate of
d𝑡
d𝑡
voltage change
Capacitors are sometimes polarized
𝜀𝐴
𝐶=
𝑑
𝜀 = Permittivity of dielectric
𝐴 = Area of plate overlap
𝑑 = distance between plates
NOTE: Directly connecting a capacitor to a voltage supply isn’t practical
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Module 3: Basic Circuits
07/08/2015
RC Circuits
Boston
RC
circuits
consist
of a resistor and capacitor in series
University
Slideshow
Title Goes Here
 How do capacitors react to a sudden change in voltage?
𝜏 ≡ 𝑅𝐶
𝑉𝑐 = 𝑉𝑠 1 − 𝑒 −𝑡
𝜏
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Module 3: Basic Circuits
07/08/2015
RC Circuits
Boston
Charge
University Slideshow Title Goes Here
 Discharge
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Module 3: Basic Circuits
07/08/2015
Experiment II
Boston
Resistor
– Capacitor (RC) Circuits
University Slideshow Title Goes Here
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Module 3: Basic Circuits
07/08/2015
Recap
Boston
What
did you
University Slideshow Title Goes Here
today?
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