Transcript E E 2440 Circuits I

E E 1205 Circuit Analysis
Lecture 1 - Introduction to Electrical
Engineering
Overview of Electrical
Engineering
• Electrical engineers design
systems with two main
objectives: to…
– Gather, store, process, transport
or present information
– Distribute, and convert energy
between different forms
• Electrical systems can be
divided into seven major
classifications.
7 Linked Classifications of Electrical
Systems
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Communications Systems
Computer Systems
Control Systems
Electromagnetics
Electronics
Power Systems
Signal Processing Systems
Communications Systems
• Telephony
– Analog and Digital
– Switched Channels
• Radio
– Broadcast AM, FM, & SW
– Two-Way
• Television
Computer Systems
• Programmable Microcircuits
• High-speed switching of logic
circuits
• Used for
– Computation
– Control
Control Systems
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Automated
Adaptable
Faster Operation than Manual
More Reliable than Manual
Modern high-performance
aircraft rely on automated
control systems
Electromagnetics
• Antennas for Sending & Receiving
Information
– Cell Phones
– Satellite Dishes
• Magnetrons for generation of Microwave
Energy
• Induction Heating for Industrial processes
Electronics
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•
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Material Properties
Devices
Circuits
Used for Detecting,
Amplifying and Switching
Electrical Signals
Power Systems
• Large networks connected by low
frequency a-c transmission lines
• Small networks in aircraft and
spacecraft
• Electromechanical Energy Conversion
• Power Electronics
– High frequency switching converters
– High efficiency, high power density
Signal Processing Systems
• Transform and manipulate
signals and the information
they contain
• Image processing
– Data from weather satellites
– MRI scans of the human body
• Noise reduction
• Encryption
Circuit Theory
• Mathematical modeling of
physical phenomena
• Circuit theory is a special case of
electromagnetic field theory
– General EM theory is more
complex than circuit theory
– General EM theory requires more
complex mathematics
Three Basic Assumptions of
Circuit Theory
• Electric effects happen
instantaneously throughout a
system
• Net Charge on every
component in the system is zero
• No magnetic coupling between
components
 cf
Effect of Frequency
Frequency
Wavelength
Usage
0 Hz (DC)
Infinite
Basic Power
60 Hz
5000 km
Power
400 Hz
750 km
Aircraft Power
1000 Hz
300 km
Acoustic
1000 kHz
300 m
AM Radio
500 MHz
60 cm
Television
2.45 GHz
122.4 mm
Microwave Oven
20 GHz
15 mm
K-band Radar
Problem Solving
• Identify what is given and
what is to be found.
• Sketch a circuit diagram or
other visual model
• Think of several solution
methods and a way of
choosing between them
• Calculate a solution
Problem Solving (continued)
• Use your creativity
– If your efforts are not converging
to a solution, you may want to
rethink your assumptions.
• Test your solution
– Is your answer reasonable?
– Does your answer validate your
assumptions?
International System of Units
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Frequency
Force
Energy or work
Power
Electric charge
Electric potential
Electric resistance
Electric conductance
hertz (Hz)
newton (N)
joule (J)
watt (W)
coulomb
volt (V)
ohm ()
siemens (S)
s-1
kg·m/s2
N·m
J/s
A·s
W/A
V/A
A/V
International System of Units
(continued)
– Electric capacitance
– Magnetic flux
– Inductance
farad (F)
C/V
weber (Wb) V·s
henry (H)
Wb/A
Standardized Prefixes
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atto
femto
pico
nano
micro
milli
centi
deci
a
f
p
n

m
c
d
10-18
10-15
10-12
10-9
10-6
10-3
10-2
10-1
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deka
hecto
kilo
mega
giga
tera
peta
exa
da
h
k
M
G
T
P
E
10
102
103
106
109
1012
1015
1018
Circuit Analysis: An
Overview
• A circuit model is used to
connect our visualization to our
analysis of a physical system
• The elements of our circuit
model are ideal circuit
components.
• The behavior of output
parameters is governed by
physical/mathematical laws for
the elements of the circuit
model.
Voltage and Current
• Voltage is the energy per unit of charge.
dw
v
dq
• Current is the rate of flow of charge.
dq
i
dt
Voltage and Current
(continued)
• The relationship between
voltage and current in a circuit
element defines that circuit
element.
• Both voltage and current have
associated polarities.
• These polarities determine the
direction of power flow.
Ideal Basic Circuit Element
• Three attributes of an ideal circuit element:
– There are only two terminals
– Described mathematically in terms of current
and/or voltage
– Cannot be subdivided into smaller components
i
+
v
-
1
2
Voltage Polarity Definitions
i
+
v
-
1
2
• Positive v
– voltage drop from 1 to 2 or
– voltage rise from 2 to 1
• Negative v
– voltage drop from 2 to 1 or
– voltage rise from 1 to 2
Current Polarity Definitions
i
+
v
-
1
2
• Positive i
– Positive charge flowing from 1 to 2
– Negative charge flowing from 2 to 1
• Negative i
– Positive charge flowing from 2 to 1
– negative charge flowing from 1 to 2
Passive Sign Convention
i
+
v
-
1
2
• Whenever the reference direction for the
current in an element is in the direction of the
reference voltage drop, use a positive sign in
any expression that relates voltage to current.
Otherwise, use a negative sign.
Power and Energy
dw  dw   dq 
p

   vi

dt  dq   dt 
• Power associated with a circuit element is
consumed by that circuit element when the
value of power is positive.
• Conversely, power is generated, or produced
by the element if the value consumed is
negative.
Expression of Power
i
i
1
+
v
-
2
1
+
v
-
2
p  vi
p  vi
i
v
+
i
1
2
p  vi
v
+
1
2
p  vi