On Apr 5, 1:14 pm, Jim Kelley wrote:
K7ITM wrote:
Hi Jim,

Some people may use only c-sub-zero for the speed of light in a
vacuum, but most commonly I see it simply as c, a fundamental physical
constant. To avoid confusion, I would HIGHLY recommend that either
you be very explicit that you're using co as the constant, and c as
the speed of light in whatever medium you're dealing with -- OR that
you're using c as the constant and whatever other notation for the
speed elsewhere.

NIST lists the constant both ways: c, c-sub-zero. SEVERAL other
places I just looked (reference books from my bookshelf; a web survey
including US, UK and European sites--mostly physics sites; several
university sites) only used c as the constant, except the NIST site
and one other, which both listed it as c or c-sub-zero with equal
weight.

It's clearly a matter only of notation, but I'll elect to stay with
the most commonly used notation, and from what I've seen just now,
most think c is a constant.

Cheers,
Tom

Hi Tom -

This is becoming circuitous. What you're saying is exactly what led
the original correspondent to be confused in the first place. Since
the relavant equation doesn't read c = f*w/n, the only way to explain
the phenomenon is by using a value of c that varies with medium. That
was the entire point.

73. Jim AC6XG

Hi Jim,

OK, but I still say that, in that case, the equation (c=f*w) uses c in
a way that's inconsistent with common usage of c. I don't know if the
article quoted by the OP mentions that, or if somewhere it adds other
qualification, but if it's not out of context, then it would confuse
me, too, if I were trying to understand it for the first time. At the
very least, the article should say somewhere that c is the speed of
propagation in whatever medium we're dealing with, and if it did,
perhaps the OP wouldn't have been confused about it in the first
place. His posting makes it very clear to me that HE thought c was a
constant, as I would if the author didn't tell me otherwise.

Cheers,
Tom