Here’s the third of three video introductions to Section 4.2, Electrical Principles, in the ARRL Extra Class License Manual for Ham Radio. This video focuses on resonance, Q, and magnetic cores, particularly on resonance. Resonance is the fundamental building block that Mother Nature provides that makes radio possible. NOTE: Lester Wetherell points out an error: “In your video amateur extra lesson 4.2 part 3 @ ~ 24 minute, made a mistake saying 10 pF = 1 X 10^-12. Just thought you should know. WD4IFU Lester.” In fact, of course 10 pF is 10 x 10^-12 farads, or in engineering notation, 10E-12 farads. You can return to the list of Amateur Extra videos by clicking here. Please leave a comment if you have comments, concerns, questions, or suggestions.