Power systems convert energy to and from electrical form. Signal processing is concerned with information-bearing
electrical signals.
• Why Study Electrical Engineering?
•
• • • • •
Control systems
and magnetic fields.
gather information with sensors and use electrical energy to control a physical process.
Electromagnetics is the study and application of electric Electronics is the study and application of materials, devices
Alternating Current
On the other hand, a current that varies with time, reversing direction periodically, is called alternating current, abbreviated as AC.
q(t ) i (t )dt q(t0 )
t0
t
Example 1.1 Determining Current Given Charge
q(t )( C )
2
0
Suppose that charge versus time is given by
q( t ) 0
t0
100t
q( t ) 2 2e
•国标符号
i
uR u uL uC R L C
+
VCC RB
a + E R0 b
IB UBE
I + U d
IC RC +
c
R
_
I B UCE
_
+ _
VCC
• Electrical Current
• Electrical current is the time rate of flow of electrical charge through a conductor or circuit element.
.
Sinusoidal current
三角波
方波
•Reference Directions
i1=-2A
i2=2A
i3=-1A
Actual Direction
•Double-Subscript Notation for Currents
Example: if iab 1A , then iba 1A
Final Score = 20% experiment performance + 30% exercise performance + 50% exam score
Electrical Engineering and Electronics II
Electrical Engineering and Electronics II
Reasons:
•To pass the Fundamentals of Engineering (FE) Examination •To have a broad knowledge and you can lead design projects in your own field •To be able to operate and maintain electrical systems •To communicate with electrical engineering consultants
and circuits used in amplifying and switching electrical signals.
Photonics is an exciting new field of science and engineering
that promises to replace conventional computing.
The electrical current flowing through the element in the reference direction is given by
dq(t ) i (t ) dt
Fig.1.4 Current is the time rate of charge flow through a cross section of conductor or circuit element
•Voltages
positive polarity positive charge
positive charge negative polarity
•Voltages’ reference polarity
Another two ways to indicate the reference polarity of a voltage: double subscripts on the voltage variable and an arrow
•Voltages
Voltages are assigned polarities that indicate the direction of energy flow. If positive charge moves from the positive polarity through the element toward the negative polarity, the element absorbs energy that appears as heat, mechanical energy, stored chemical energy, or as some other form. On the other hand, if positive charge moves from the negative polarity toward the positive polarity, the element supplies energy.
-
+
Vab=-5V
Vba=-Vab
1.3 Power And Energy
Consider the circuit element shown in Figure 1.14. Because the current i is the rate of flow of charge and the voltage v is a measure of the energy transferred per unit of charge, the product of the current and the voltage is the rate of energy transfer. In other words, the product of current and voltage is power.
1.1 Overview of Electrical Engineering
Electrical systems have two main objectives: • To gather(采集), store(存储), process (处理) , transport(转换), and present(显示） information • To distribute and convert energy between various forms
Chapter 1 Introduction
4 Course Hours
1. Introduction
1.1 Overview of Electrical Engineering 1.2 Circuits, Currents, and Voltages 1.3 Power and Energy 1.4 Kirchhoff's Current Law 1.5 Kirchhoff's Voltage Law 1.6 Introduction to Circuit Elements 1.7 Introduction to Circuits
Electrical Engineering and Electronics II
Electrical Engineering
Principles and Applications
Hale Waihona Puke Chen Qiangsdnjchq@
Electrical Engineering and Electronics II
t
400
t0
dq(t ) Solution : i (t ) dt 0 t0 200e 100t
i (t ) 200e 100t
t 0
200
t0 0
t ( ms)
Direct Current
When a current’s direction is constant with time, we say that we have direct current, abbreviated as DC.
•Voltages
The voltage associated with a circuit element is the energy transferred per unit of charge that flows through the element. The units of voltage are volts (V), which are equivalent to joules per coulomb (J/C).