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Unit 2: Introduction to Alternating Current and Voltage

In EET 1150 you learned how to analyze circuits containing DC (direct-current) sources. In this course you’ll learn how to analyze circuits containing AC (alternating-current) sources. AC electricity is more complicated than DC, so this unit will introduce some concepts and terms that we’ll use for the rest of the course.

But we will pick up some new ideas, such as angular frequency and a way to write mathematical expressions for sinusoidal waves. For instance, here’s a mathematical expression that describes a particular sinusoidal voltage:

     v = 4.62  V sin(968t + 50°).

At first sight, this may look complicated, but with a bit of practice you’ll be able to interpret and use expressions of this kind.

In this unit we’ll get a start on analyzing AC circuits. Fortunately, resistors in AC circuits behave pretty much the same way they behave in DC circuits. Therefore, you can use circuit rules that you already know–such as Ohm’s Law, Kirchhoff’s Voltage Law, and Kirchoff’s Current Law–in pretty much the same way that you used them in DC circuits. (But as we’ll see in later units, inductors and capacitors behave one way in DC circuits, and they behave entirely differently in AC circuits.)

Unit 1 Review

DC and AC
AC versus Pulsating DC
Sine Wave
Sinusoids In, Sinusoids Out
Periodic Waveform

Waveform Parameters
How Period and Frequency Are Related
Instantaneous Value
Peak Value
Peak-to-Peak Value 
p and pp

Function Generator
Using the Oscilloscope to Measure Voltage
Using the Oscilloscope to Measure Period and Frequency
Oscilloscope Challenge Game

Different Ways to Give AC Values
RMS Value (or Effective Value)
Relationship Between Peak Values & RMS Values
Multimeter for AC
True rms Meter

Average Value

Phase of a Sine Wave
Converting Between Degrees and Radians
Phase Shift
Lead and Lag
Using the Oscilloscope to Measure Phase Shifts

Lowercase and Uppercase
Mathematical Expression for a Sine Wave 
Mathematical Expression for a Phase-Shifted Wave

Rotating Phasors
Phasor Diagrams
Angular Frequency
Vp sin(ωt)
Instantaneous Value
General Form of a Sinusoid

Analyzing AC Circuits
Sinusoids In, Sinusoids Out
Phase in Resistors
Ohm’s Law for Resistors
KVL and KCL for AC Circuits
Power in a Resistor

Superimposed DC and AC Voltages 

Review of Electrical Quantities

Unit 2 Review

Congratulations! You’ve completed the e-Lesson for this unit.