Neville Munn wrote:
Apologies for the appalling way in which I put my queries, and
I'll answer in one go here.
1) Particle size and beam strength: What I meant to say
was...although the other colour reflected/refracted? is grey and
unseen with naked eye, if the light beam is 'reflected' from the
larger particles among the smaller particles, could that be a
misguided belief that there are a large number of larger particles
present in a given solution, when in actual fact there isn't?
Example: Lemon yellow solution {although this would apply to a clear
solution as well}...shine laser thru solution...strong beam of light
suggesting larger particles, BUT, could that beam strength also
indicate light 'refracting?' off those larger particles and as it
scatters in the liquid 'reflect?' light off the smaller ones, giving
the illusion that there are *many* larger particles in solution due to
beam strength, when if fact there may be a *lesser* number of larger
particles but the beam strength indicates otherwise.
As I indicated before the liquid is isotropic, thus whether any photons
refracted then hit a small particle is irrelevant, the probability of
hitting a small particle is the same regardless of what direction the
photon is moving. However if it is refracted it could end up outside of
the beam when it hits a particle, thus in actuality refraction would
result in a slight reduction in the intensity of the beam.
In a clear solution that beam would just appear stronger than perhaps
it otherwise would in a clear solution with minimal larger particles.
Jeez, I don't know if this is decipherable either?
Look at the equations, they tell the complete story. Reflection off a
particle goes up by the 6th power of the size of that particle. So if
you have 1% large particles which are 10 times bigger than 99% small
particles (by count, not ppm), then the amount of light coming off the
large particles will be 10^6/100, or 10,000 times as bright as what is
coming off the small particles even though they only account for 1% of
the partiles..
I'll move on to the other one...
2) Laser failing to pass thru liquid: Shone light thru
solution...puts spot on wall as light exits glass but no path thru
liquid. I believe both you and Dok have answered this one now.
Although you're right regarding spot 'size' on wall, I've switched
batteries over from laser with larger spot size {now there's the
appropriate larger spot size on wall with this laser} and there
appears to be little difference. If I look *real* close I can see a
*very* faint beam, but when batteries are returned to original laser
that beam is *very* evident. This suggests to me that there is a
basic difference in construction of both lasers {for the want of
better description}.
Laser light is laser light. If you are seeing a difference then it is
going to be either a difference in the intensity of the beam, or a lack
of coherence implying tht one is not lasing, provided they are the same
wavelength.
I believe I understand the different apearance of a laser spot as
compared to an LED. An led couldn't really be defined as a 'spot',
besides, they won't light up the trees 15 streets away with a 'spot'.
A laser beam is both coherent as well as columinated. An LED is
neither. A non lasing laser is an LED.
Marshall
If I still haven't made myself clear I guess we'll have to put it down
to a "failure to communicate" with the uneducated.
Your 'spot size on wall' indictor for the laser is very useful too
Marshall, Thanks very much for that. I knew there was a reason I
don't participate in other discussion groups anymore <g>.
N.
> Date: Thu, 15 Apr 2010 11:09:51 -0400
> From: [email protected]
> To: [email protected]
> Subject: Re: CS>Serious EIS Colour Size/Zeta=[Malvern DLS]
>
> You might be correct there, but I had assumed that the statement
that it
> was throwing a good spot on the wall meant that it was lasing. If the
> spot is more than 1/4 inch in diameter at 10 feet, then it would not be
> a good spot on the wall as far as I am concerned. So, how big is the
> spot on the wall at 10 to 20 feet? Should be about the size of a
> pencil. If it is bigger then the laser is not lasing and is nothing
> more than an LED.
>
> Marshall
>
>
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