E E 1205 Circuit Analysis

1
E E 1205 Circuit Analysis

• Lecture 1 - Introduction to Electrical
  Engineering

2
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.

3
7 Linked Classifications of Electrical Systems

• Communications Systems
• Computer Systems
• Control Systems
• Electromagnetics
• Electronics
• Power Systems
• Signal Processing Systems

4
Communications Systems

• Telephony
• Analog and Digital
• Switched Channels
• Radio
• Broadcast AM, FM, SW
• Two-Way
• Television

5
Computer Systems

• Programmable Microcircuits
• High-speed switching of logic circuits
• Used for
• Computation
• Control

6
Control Systems

• Automated
• Adaptable
• Faster Operation than Manual
• More Reliable than Manual
• Modern high-performance aircraft rely on
  automated control systems

7
Electromagnetics

• Antennas for Sending Receiving Information
• Cell Phones
• Satellite Dishes
• Magnetrons for generation of Microwave Energy
• Induction Heating for Industrial processes

8
Electronics

• Material Properties
• Devices
• Circuits
• Used for Detecting, Amplifying and Switching
  Electrical Signals

9
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

10
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

11
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

12
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

13
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
14
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

15
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?

16
International System of Units

• Frequency hertz (Hz) s-1
• Force newton (N) kgm/s2
• Energy or work joule (J) Nm
• Power watt (W) J/s
• Electric charge coulomb As
• Electric potential volt (V) W/A
• Electric resistance ohm (?) V/A
• Electric conductance siemens (S) A/V

17
International System of Units (continued)

• Electric capacitance farad (F) C/V
• Magnetic flux weber (Wb) Vs
• Inductance henry (H) Wb/A

18
Standardized Prefixes

• atto a 10-18
• femto f 10-15
• pico p 10-12
• nano n 10-9
• micro ? 10-6
• milli m 10-3
• centi c 10-2
• deci d 10-1

• deka da 10
• hecto h 102
• kilo k 103
• mega M 106
• giga G 109
• tera T 1012
• peta P 1015
• exa E 1018

19
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.

20
Voltage and Current

• Voltage is the energy per unit of charge.

• Current is the rate of flow of charge.

21
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.

22
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

23
Voltage Polarity Definitions

• 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

24
Current Polarity Definitions

• 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

25
Passive Sign Convention

• 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.

26
Power and Energy

• 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.

27
Expression of Power