Re: [Phys-L] Inverse Square for reflected light

[John Denker <jsd@av8n.com>]

On 12/8/21 9:34 AM, Scott Goelzer via Phys-l wrote:

> using a Pasco light meter and a standard ray box

1) I hate to ask dumb questions, but.... 
Have they got the geometry right?

1a) I can imagine scenarios where they move the mirror in
such a way that the image does not "fill" the mirror; that 
is, the edge of the mirror cuts off some of the beam.

1b) I can imagine scenarios where the sensor module blocks
the beam on its way from the source to the mirror.




2) The "ray box" can be used in lots of ways.
Much depends on what you consider "standard".

It can be configured to put out a large beam that is
more-or-less collimated:

	_______________________________
	_______________________________
	_______________________________


Or a beam that diverges from a more-or-less point source:

           /
          /
         /
        /_____________
        \
         \
          \
           \


So you can have a dependence that goes like 1/x⁰ or 1/x² or
anything in between. In general you will get non-power-law
behavior that only asymptotically settles down to a power law.


> Best explanation I could give was that the mirror was not functioning
> as a point source any longer and was producing effectively parallel
> wave fronts.

That leaves us with the obvious follow-up question: why would
it do that?

If the mirror is behaving as normal mirror, the method of
images should apply. That is, the situation should look like
light being emitted from the image.

> some photography sites confirm the effect without explanation

Reference?