Re: Do you see what I see?

[roger haar <haar@soliton.physics.arizona.edu>]

Hi,
	

	Item 1 on the bowing line.  I tried it and saw the moving.
I used a bit of cardstock instead of my finger to get a sharp edge.
I observed that the bowing started when the outermost blur of the edge of 
the card started to eclipse the line (actually I used my door frame).
Also the line appears to narrow.
	For introductory textbook optics, blocking half of the rays 
should not cause the focused image to move.  The direction of motion is 
consistant with the focus of the eye being a bit short of theposition of 
the line.  This shortening of the focus of the eye could be in response to 
the new object (the finger) in its viewing field.  There are enough 
oddities in the human eye that this is probably just a wild guess.   

 

	Item 2 on flourescenct paints,  True florescent paints absorb 
light a higher frequencies and re-emit the part of the energy at a lower
frequency.  The classic example of this is fabric whitener which absorb
UV and emit blue.  If you dispere the light from a mercury bulb using a 
grating and project it onto a sheet of white paper you can probably
see lines on the paper that are actually UV.

	Item 3 on colors.  The spectra of molecules is different 
than those of atoms in the the absorption lines for atoms are
very narrow while the lines for molecules are broad lines or bands.
For gas  molecules, in addition to the electronic transitions there are 
rotation and vibrational levels that are small relative to the electronic 
levels and appear in the spectrum as the broadening of the electronic 
transition lines.  
	For solids, it is the widths, and separation of the filled and 
unfilled electron band structure that determines what wavelength of light 
can be absorbed.  Usually the light energy is converted to thermal energy,
but in the case of the flourescent paints, the molecules de-excite by
emitting light.  Usually there is more than one transition by which the
excited state can de-excite.  If the transition associated with lower 
wavelength on is more probable than one gets something like fabric 
whiteners as in Item 2



****************************************************************

On Wed, 27 Nov 1996, Ken Kiehlbauch wrote:

> Here are three somewhat related questions:
>
> 1. Draw a vertical chalk line on the blackboard and then step back a few
> meters.  With your index finger a few inches in front of your eye,
> slowly push it across the line.  Just before your finger eclipses the
> line, the line will seem to bow ahead of your finger.  Is this due to
> diffraction, the width of the pupil, or ????
>
> 2. Why do so called "flourescent" colors (hot pink, day glo orange) seem
> so bright.  Nothing can reflect more light than white, and any dye only
> produces a color other than white by absorbing wavelengths.  So why do
> these colors seem to leap out at me?
>
> 3. In all my years of teaching physics, I have never seen an explanation
> of how surfaces produce their characteristic color.  I know well enough
> that matte red paper is red because it absorbs all colors but red (and
> most likely some orange), but how are all the all other colors
> absorbed?  How can the molecules absorb a tremendous range of
> frequencies at once?  And how can one group of frequencies reflect off
> this surface?  Is it reflected or reemitted?  What's the actual
> mechanism involved?
>
> Thanks for the expertise of those who repond.
>
> Ken Kiehlbauch
> Faith Academy
> Manila, Philippines