Tuesday, January 18, 2011

Lesson 23: General Class Exam Course G6A

Hello again!  Here is lesson 23 covering the G6A questions from the question pool.  The questions deal specifically with resistors, capacitors, and inductors.  More specifically, quirks with these types of components.  Depending on the situation, sometimes a capacitor may inadvertently act like and inductor, an inductor may act like a capacitor, and a wire-wound resistor may act like an inductor.  How much these components decide to pretend to be other components depends primarily on their design and the frequency of AC.  It is important to understand because these issues can cause a lot of problems, especially in tuned circuits.

Another quirk with resistors is they are temperature sensitive.  Depending on the resistor, as temperature increases or decreases their resistance value may increase or decrease as well.  The other problem is that this change in resistance with temperature is not universal for all resistors.  Some resistors increase resistance as their temperature increases, some decrease resistance as their temperature increases.  Resistors have a temperature coefficient rating (sometimes called tempco) which tells how they react to temperature.  A positive temperature coefficient means resistance increases as temperature increases.  A negative temperature coefficient means as temperature increases, resistance decreases.

There is one question that you will want to memorize, unless you are familiar with filters:

A filter choke is the common name for an inductor used to help smooth the DC output from the rectifier in a conventional power supply.

As always, please leave any suggestions, comments, or questions in the comments box.  Thanks!

73,
Andy
KE4GKP

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