Reader Feedback
Dear Nuts & Volts:
I was taken back to my college
days at the University of Colorado by
the article “A New Life for LORAN”
(August 2004). I took power lab from
Prof. Easton and electronic lab from
Prof. Wicks in the same semester.
There was a friendly exchange of
barbs between the two; in particular,
Prof. Easton accused the circuits lab
of dealing in “sneak currents,”
milliamps vs. real currents of dozens
or even hundreds of amps in the
power lab. The last day of class, Prof.
Wicks distributed data sheets for the
F1086 tube, pointing out that the
12.6 volt AC filaments ran 200 amps,
asking us to “Tell Prof. Easton that
this is not a sneak current!” when we
went to the final power lab class.
Thanks for the memory.
Jerry Berry, BSEE ' 59
via Internet
Gernsback. This is the first complete
account I have ever seen of his life
and accomplishments. Those of us
who got our start in radio in the
1930s well remember waiting in
anticipation each month for the latest
issue of his Shortwave Craft (if I have
the name right?).
Paul Rafford Jr. NY4L
via Internet
Dear Nuts & Volts:
Having been a Loran A instructor
during World War II, and having
conducted the first airline evaluation of
Loran C in the 1950s, I was surprised
to learn from Clifford Appel's article in
your August issue that Loran C is still
alive and pulsing. However, he fails to
mention what agencies might use it
today. Considering that GPS seems to
have become the method of
preference for geographic position
fixing in the 21st century, I would have
thought that Loran C would have gone
the way of Decca/Dectra, Omega, and
the other navigational systems of the
20th century.
Also, I was very interested in
Michael Banks' article about Hugo
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Dear Nuts & Volts:
While thumbing through your
August 2004 issue, I came to the article
“Just for Starters” by Mark Balch and
was happy to see a section titled Ohm's
Law. One of my minor hobbies is
analyzing explanations of “Ohm's Law
for beginners” to see how close to the
truth the author came. (What does that
tell you about my life!?)
People who work with objects that
conduct electricity are often interested
in knowing the current I that flows
when a voltage E is applied, and the
ratio of E/I of these quantities. This
ratio turns up so often that it is handy
to have a name and symbol for it, and
in fact it has been given the name
“resistance” and the symbol R. Thus,
the expression R=E/I is not any kind
of law, but simply a definition of
resistance. Ohm's Law, on the other
hand, is more significant than this. It
is an experimentally determined law
of nature, not just a definition.
So what is Ohm's Law? If we apply
voltage E1 and measure current I1,
and then apply a different voltage E2
and measure current I2, Ohm's Law
states that E1/I1 will be equal to E2/I2.
Since we have made a definition for the
ratio E/I, and since the test voltages
were arbitrary, another way to
say this is R=constant. In other
words, Ohm's Law states that
the resistance of a conductor
stays the same for any applied
voltage. Since we all know this
isn't true (visualize the
characteristic curve of a silicon
diode), why is Ohm's Law
important? The answer, of
course, is because lots of
important devices do obey the
Law for a wide range of voltages
and currents. The diode just isn't
one of them. Even for the
diode, we can use the definition
to calculate an effective
resistance for a given voltage or
current. But when we do this,
(Continued on Page 45)
by J. Shuman
6
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