MRW wrote:
On Apr 5, 4:40 pm, Roy Lewallen wrote:
Yes. And it's very, very nearly the same for air.

The 30,000 km would be a typo -- the wavelength in a vacuum at 10 kHz
would be 30 km.

Roy Lewallen, W7EL

Thanks again everyone! It makes sense to me to just treat c, in this
case, as a relative speed dependent on the medium.

As others have pointed out, it's risky to treat c as a variable or
medium-dependent speed. That letter is nearly always used to designate
the speed of light (or any EM plane wave) in a vacuum. Using that
nearly-universal definition, the speed of an EM wave in any other medium
is VF * c where VF is the "velocity factor". It's important to realize
that while there's a single value for the speed of all EM waves in a
vacuum (c), this isn't true in many other media. In many media, the
speed of the wave depends on its frequency, a phenomenon called
"dispersion". So in many media there's no universal EM velocity
equivalent to c, but rather a frequency-dependent velocity factor.

In environments where the field is confined such as a waveguide, the
velocity can also depend on the mode, that is the orientation of the
fields. So there's not even a single value for each frequency. And this
can be true even if the waveguide is filled with a vacuum.

Roy Lewallen, W7EL