Neville Munn wrote:
OK, I'll tackle this from another angle and see if this prompts a
response.
I'll start with what Marshall said earlier, and I'm discussing the use
of a 650nm red laser operating at <1mW here.
Apparently Tyndall in a yellow solution signifies particles of around
50nm {correct me if I'm wrong Marshall} so what would one observe if
using a 750nm laser, or an 850nm laser, or a 1000nm laser for
observation of particles in solution, assuming that those particles
present ARE around that 50nm range? Would there be NO change to
Tyndall? Stonger Tyndall? Weaker Tyndall? Praps NO Tyndall even?
I posted the equations earlier. The Tyndall goes DOWN with increases
in wavelength, that is why the sky is blue (lots of Tyndall in the blue
range, virtually none in the red). But of course you won't be able to
see the 850 or 1000 since they are both infrared, although an infrared
camera might pick them up.
Do the varying operating wavelengths in different lasers alter any
characteristics of that laser when used for particle detection in
solution?
Just the efficiency of the Tyndall goes down with increase in wavelength.
Marshall
N.
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From: [email protected]
To: [email protected]
Date: Tue, 4 May 2010 17:08:01 +1030
Subject: CS>Tyndall cone...or lack of?
Well, apart from a couple of comments suggesting a possible lack of
particles in solution {which is not applicable I might add} it would
appear nobody has an explanation, or has ever experienced my little
quandary with lasers?
Praps one of the more 'knowledgable' folk among us who are into
experimentation and/or research {gurus <g>} may wish to pick the ball
up and run with it by getting hold of a red laser of <1mW and run the
batteries down and see if they get a similar occurrance, although, if
my issue happens with an El Cheapo freebie laser I can't see why it
wouldn't do the same thing with my more expensive ones, lasers are
lasers. They either operate, or they don't...DO THEY?
It's fine to assume that battery power falling below *some?* threshold
may affect the operational function of a laser, nevertheless it
doesn't afford a suitable explanation as to what one would expect to
observe in such an eventuallity when making observations of colloids
in liquids?
At this stage I've gotta be thinking the use of lasers for determining
pretty much *anything* with solutions is questionable...[battery
reserve dependant!] That could be a trap for young players I suspect.
Guess I'll just have to wait til some batteries have drained in one of
my other more expensive lasers and do some more observations to find
out. BUT, it still won't give me an explanation as to WHY the light
fails to backscatter off particles as it passes through that liquid?
How about this then...
What if I were to suggest that if battery power falls below a specific
operational threshold it may alter the wavelength and if particles are
smaller than that wavelength then the light may pass *straight
through* the liquid but the particles FAIL to backscatter that light?
N.
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