Transcript Document

A long time ago, in a galaxy
far, far away….
1-1
Chapters I & II
CIRCUIT VARIABLES AND
ELEMENTS
The Empire is bad, mmkay? But
we’re not here to talk about that.
We’re here to learn circuits! So
lets get started!
1-2
Agenda
• Overview of Electrical Engineering
• This Particular Course
• SI Units and Engineering Notation
• Voltage Current Energy Power
1-3
25
Chapter Goals
• Circuit Elements
• Circuit Theory
• Constructing a Circuit Model
• Circuit Analysis with Dependent Sources
1-4
25
Electrical Engineering Subfields
• Communication - Telephones, radios, microwave
communications. Conversion, transmission, and processing of
analog electromagnetic signals
• Computer - EE’s build analog devices that deal with discrete
voltage levels (bits).
• Control - Use electrical signals to regulate processes. Cruise
control, elevators, rockets.
• Power - Generating and distributing electrical power.
• Signal Processing - MRI’s, CAT scans (image processing)
Converting signals to an intelligible form. (Big field now is
Digital Signal Processing (DSP) where analog signals are first
digitized, then processed digitally.)
1-5
THE COURSE IN A
NUTSHELL
1-6
The Course in a Nutshell
• First course in engineering analysis – we
are learning engineering analysis
methodology – Methodology is NOT
limited to just circuits
• How to construct, analyze and solve
mathematical circuit models, in
particularly interested in:
–Voltage, Current, Energy, Power
1-7
!!MODELING!!
• Modeling is and important engineering
skill
• Perhaps THE MOST IMPORTANT
engineering skill
• Kinds of engineering models
– Circuits, drawings, system diagrams, process flow
charts
1-8
N
A
V
1C
kg
J smm
sA s 2
V
C
Important SI Units
Quantity
frequency
force
energy or work
power
charge
potential
resistance
Unit
hertz
newton
joule
watt
coulomb
volt
ohm
Symbol
HZ
N
J
W
C
V
Ω
Formula
1/s
Kg*m/s^2
N*m
J/s
A/s
J/C
V/A
1-9
5
Engineering Notation
• Engineers mostly use the powers divisible by
three, and keep the base number between 1
and 1000.
• ex) 0.000044 seconds= 4 x 10-6 s = 44 µs
• ex) 87625622 volts = 87.6 x 106 V = 87.6 MV
(typically rounded to 3 sigfigs, that’s 1%!!)
1-10
5
VOLTAGE
CURRENT
ENERGY
POWER
1-11
Voltage
The energy of charge separation, or,
The work required to separate charges
volts = Joule/Coulomb
Voltage = Energy/Charge
Analogous to water pressure
1-12
Current
The flow rate of charged particles:
• Amp = Coulomb/Second
• Analogous to water flowing
1-13
Energy
Difficult to intuitively define, actually.
Richard Feynman, "It is important to realize that
in physics today, we have no knowledge what
energy is. We do not have a picture that
energy comes in little blobs of a definite
amount.".
1-14
Energy: Lets’ try again
Comes in many interchangeable forms.
Easiest form to understand is probably WORK
Work = Force * Displacement
[J = N*m]
Other forms of energy are
Heat, kinetic, chemical, electrical, nuclear, etc
1-15
Power
The RATE of energy use:
Watt = Joule / Second
Can be high powered like a rocket
Use up 1 gallon of gas in 1 second
Can be low powered like a scooter
Use up 1 gallon of gas in 1 hour
1-16
More about Power and Energy
Energy and power are always CONSERVED
That is, they can change form but are never created or
destroyed (in classical Newtonian physics)
(But sometimes they leave our system boundaries)
p = iv
p = i2 * R
p = v2 / R
1-17
CIRCUIT
ELEMENTS
1-18
Circuit Elements
•
•
•
•
•
Voltage sources
Current sources
Resistors
Capacitors
Inductors
1-19
2
Voltage and Current Sources
Voltage sources
Direct
Alternating
Function-driven
Independent
Dependent
1-20
2
Resistors
Resist the flow of current
Energy (voltage) is required to
force current thru them
this “voltage energy” is
transformed to heat
analogous to a valve like a faucet
Ohms’ Law: v = iR
1-21
2
Capacitors
Stores up and releases charge
(energy) depending on the
change in voltage
i = C dv/dt
i is the “displacement current”
cuz the dielectric it does not
conduct current
1-22
2
Inductors
Stores up and releases (voltage)
energy depending on the
change in current
v = L di/dt
1-23
2
CIRCUIT
THEORY
1-24
Circuit Theory
1. A Circuit is a mathematical models that
approximates the behavior of an actual
physical system
2. Circuit Theory is the study of electrical
charges (simpler than emphasizing
magnetic fields, although magnetism is a
factor)
1-25
2
Some Basic Assumptions
(simplifications)
1. Electric Effects happens instantaneously
throughout the system. aka “lumped parameter
system”
2. The net charge on every component is always
zero.
3. There is no (usually) magnetic coupling between
components.
4. Conductors (usually) have no resistance
5. Elements are “ideal” – they obey our math
models
1-26
2
A SIMPLE
CIRCUIT MODEL
1-27
A Flashlight Circuit Model
• Constant ideal independent
voltage source
• Ideal Resistor (light bulb)
• Ideal conductor (zero resistance)
• Ohm’s law applies
• KCL and KVL apply
• Power laws apply
(Instructor will now do amazing mathematical things with this model)
!MODELING! Real v Ideal
• Constant ideal independent
voltage source
– Contrast with real battery
• Ideal Resistor (light bulb)
– Contrast with real light bulb
• Ideal conductor (zero resistance)
– Contrast with real conductor
• Other effects
– inductance, capacitance, etc