Saturday, January 1, 2011

Lesson 20: General Class Exam Course G5A

Hello again!  Here is lesson 20 and the G5A questions from the exam question pool.  This lesson deals with impedance, reactance, and resistance. 

A lot of the time impedance is associated with antennas and antenna matching.  Impedance is much more broad of a topic.  Impedance matching is important to maximize the transfer of power.  The more closely the impedance is matched between the power source and the load, the more efficient the transfer of power is.  For the purposes of the exam, impedance is the opposition to current flow in an AC circuit.  Resistance and reactance are both types of impedance. 

Reactance is the other new term in this lesson.  Reactance is the opposition to the flow of current in an AC circuit caused by capacitance and/or inductance.  The electric field created by capacitors and the magnetic field created by inductors react to the constant reversal of current direction in AC circuits.  As the frequency of the AC current increases, the reactance (or opposition of current flow) caused by inductors increases.  For inductors, the higher the AC frequency, the higher the reactance.  Capacitors are just the opposite,  The higher the AC frequency, the lower the reactance caused by the capacitor.

Impedance, reactance, and resistance are all measured in Ohms.

If you have any suggestions, comments, or questions, please feel free to leave them in the comments box.  Thanks!


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