[AMRadio] Extra Class isn't dumbed down? (was Viking 1)


Jim Liles hallicrafterssr2000 at k9axn.com
Wed Dec 23 21:03:59 EST 2015


Thanks Nick, Dan, and Don,

Nick, interesting you brought Maxwell's work front and center.  His third and fourth equations proving that displacing a magnetic or electric field in time and space would precipitate electromagnetic radiation.  These were the genesis for Einstein's theory of relativity.  It also proved that a displaced magnetic or electric field radiate exactly equally.  That’s for another time regarding antennas.

The reasons regarding most of these concepts were taught in Physics classes until somewhere in the 70’s when the emphasis was redirected to Computer assisted design tools.  Had a Professor in the early 60’s who taught what is now Physics, Applied Physics, and the logic track in Philosophy; he loved to present analogies.  One of the dozens that he used was inductive reactance and behavior.  After Jan 1 I’ll wrap words around the inductive reactance and 90 degree analogy and add it to my web site.  Doesn’t require complex equations, simply easy to understand logic.   

Kindest regards Jim K9AXN  





-----Original Message----- 
From: Nick England 
Sent: Wednesday, December 23, 2015 4:41 AM 
To: Jim Liles 
Cc: Rob Atkinson ; Discussion of AM Radio in the Amateur Service 
Subject: Re: [AMRadio] Extra Class isn't dumbed down? (was Viking 1) 

See Maxwell's equations but basically what Rob said. For an inductor v=Ldi/dt. So current through an inductor is proportional to the integral over time of the voltage.  The integral of a steady state sine wave is a sine wave lagging by 90 degrees. For the first cycle you probably need Laplace transforms to figure it out exactly but that course was a long time ago.  
Howzzat?

On Tuesday, December 22, 2015, Jim Liles <hallicrafterssr2000 at k9axn.com> wrote:
Hi Rob,

I wasn't suggesting memorizing everything.  I suggested that we all memorize
formulas and concepts not just newbies.  Now, because they may memorize more
than others doesn't qualify them for target practice.

Rob, your comment "Current lags in an inductor because the field is induced
first but the bulk of the current doesn't flow until the field collapses" is
not what I was looking for.

The question that I ask is "How does the current get to the point that it
lags the voltage by 90 degrees in an inductor?".

That's a universally asked question by new comers to the hobby including
myself 62 years ago as a Novice.

Explain it using a single sine wave applied to an inductor; don't cloud the
explanation with resistance, just inductance.  Don't worry about the values,
explain how and at what time during that first cycle there is a 90 degree
relationship: or any cycle after the first.

Articulate the phase relationship at the end of each 1/4 cycle.

I asked this because rote learned concepts do not necessarily mean there is
understanding; but they are a good starting point.

If this is of no interest to anyone simply erase it and I will simply
evaporate.  Some may find it interesting.

Kindest regards Jim K9AXN






-----Original Message----- From: Rob Atkinson
Sent: Tuesday, December 22, 2015 5:22 AM
To: Jim Liles
Cc: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] Extra Class isn't dumbed down? (was Viking 1)

Current lags in an inductor because the field is induced first but the
bulk of the current doesn't flow until the field collapses.

you can't justify memorizing _everything_ because many have memorized
math formulas.  Sorry, but that's a false analogy.  Try something
else; good luck.

73 Merry Christmas

Rob
K5UJ 
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-- 

Nick England K4NYW
www.navy-radio.com


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