1. Introduction to Electric Circuits – Engr 240
Lecture 1
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

2. Definitions Engineering (Webster) Electrical Engineering (Webster)
A science by which the properties of matter and the sources of energy are made useful to mankind
Electrical Engineering (Webster)
A science by which the properties of matter and the sources of electrical energy are made useful to mankind
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

3. History
1884
American Institute of Electrical Engineers (AIEE) formed as professional society for electrical engineers
1912
Institute of Radio Engineers (IRE) formed as professional society for radio engineers
1963
Institute of Electrical and Electronics (IEEE) formed as merger of AIEE and IRE
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

4. Branches of Electrical Engineering
Electric Utility Industry
Generation, Transmission, Distribution, Utilization
Electronics Industry
Communications, Signal/Image Processing, Analog/Digital Electronics, IC Design, VLSI
Computer Industry
Hardware, Software
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

5. Circuit Theory Commonality among different branches?
Yes, electric circuits
Electric Circuit
A mathematical model that approximates the behavior of an actual electrical system
Circuit theory is a special case of electromagnetic field theory
The study of static and moving electric charges
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

6. Assumptions
Electrical effect happen instantaneously throughout a system
The net charge on every component in the system is always zero
There is no magnetic coupling between the components in a system
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

7. Problem Solving Identify what’s given and what’s to be found
Sketch a circuit diagram or other visual model
Think of several solution methods and decide on a way of choosing among them
Calculate a solution
Use your creativity
Test your solution
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

8. The International System of Units (SI)
SI units are based on six defined quantities
Length (meter, m)
Mass (gram, g)
Time (second , s)
Electric current (ampere, A)
Thermodynamic temperature (degree kelvin, K)
Luminous intensity (candela, cd)
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

9. SI Standard Prefix Prefix Symbol Power atto a 10-18 femto f 10-15 pico
10-12
nano n
10-9
micro 
10-6
mili 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
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

10. Voltage and Current
Electric charge is the basis for describing all electrical phenomena
Important characteristics of electric charge (q):
Bipolar (+, -)
Electron (-), Proton (+)
Discrete quantities, x10-19 C
Electron ( x10-19 C), Proton ( x10-19 C), Neutron (0 C)
Electrical effects are attributed to both separation of charge (voltage) and charges in motion (current)
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

11. Voltage The separation of charge creates an electric force
Whenever positive and negative charges are separated, energy is expended
Voltage is the energy per unit charge created by the separation
where
v = the voltage in volts
w = the energy in joules
q = the charge in coulombs
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

12. Current The motion of charge creates an electric fluid
The electrical effects caused by charges in motion depend on the rate of charge flow
The rate of charge flow is known as the electric current
where
i = the current in amperes
q = the charge in coulombs
t = the time in seconds
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

13. Ideal Basic Circuit Element
Attributes:
Only two terminals
Describes in terms of current and/or voltage
Cannot be subdivided into other elements v
voltage drop from terminal 1 to terminal 2 or
voltage rise from terminal 2 to terminal 1 i 1 2 + - v i
positive charge flowing from terminal 1 to terminal 2 or
negative charge flowing from terminal 2 to terminal 1
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

14. Power and Energy
Power is the time rate of expending or absorbing energy
where
p = the power in watts
w = the energy in joules
t = the time in seconds
Power is associated with the flow of charge
where
p = the power in watts
v = the voltage in volts
i = the current in amperes
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

15. Power Polarity p = vi p = -vi p = -vi p = vi 1 2 + - v i 1 2 + - v i 1
Department of Electrical and Computer Engineering, Boise State University, SML, Fall 2003

16. Algebraic Sign of Power
Power is being delivered to the circuit inside the box
- (p<0)
Power is being extracted from the circuit inside the box

17. Reading Assignment
Chapter 1
Chapter 2