Re: natural/resonant frequency of water molecules

PD wrote:
On Apr 9, 3:38 pm, none <""doug\"@(none)"> wrote:
PD wrote:
On Apr 9, 2:25 pm, j...@xxxxxxxxxxxxxxxxxxxx wrote:
PD <TheDraperFam...@xxxxxxxxx> wrote:
On Apr 9, 1:20?pm, none <""doug\"@(none)"> wrote:
PD wrote:
On Apr 8, 4:49 pm, ssylee <sta***...@xxxxxxxxx> wrote:
Does anyone happen to know what's the resonant frequency of water
molecules? I'm having a lot of trouble finding it on google.
Hint: Microwave ovens operate on the principle of exciting resonant
vibrations of water molecules.
Sorry, but I have to disagree with this one. They operate on the
principle that lossy conductors get hot in an applied field.
Yes, that's true, but the 2.4GHz frequency is also matched to a set of
resonant frequencies in water, sugars, and oils:
http://home.howstuffworks.com/microwave1.htm
That's why that frequency is chosen.
Actually that part of the spectrum was designated for industrial
machinery because water absorption at those frequencies makes it
unhandy for things like communication and radar.
When microwave ovens came along they were dumped in there because
they are concidered industrial machines.
Serendipity then.
"Can't use these frequencies. Water gets in the way. Throw it to the
machines."
"Throw the ovens in with the machines."
"The oven needs to shake water. Wonder what frequency we should use."
PD
The other reason for picking a frequency in that range is that the skin
depth in materials like meat is on the order of a few cm at those
frequencies so the absorption is good. If the skin depth is too large,
the coupling is poor and if it is too small, only the surface gets
warm.

The interesting part about this is that 2.5 GHz is a lousy frequency
for *ice*. This is part of the reason why the defrost cycle on
microwave ovens is just a 20-30% duty cycle. What this accomplishes is
that the microwaves heat the *water* during the "on" part, and then
the heat passes to and melts the ice on the "off" part.

PD
The reason for this is that the conductivity is ionic and the number
of ions varies exponentially with temperature.
.