Re: [Phys-L] Inverse Square for reflected light (Scott Goelzer)

[Scott Orshan <sdorshan@aol.com>]

You have to measure the full path from the light source to the mirror 
and then to the light meter. If you just measure the distance from the 
light meter to the mirror, doubling that distance is not doubling the 
path length, i.e., the distance to the virtual image of the source.

On 12/8/2021 12:00 PM, phys-l-request@mail.phys-l.org wrote:
> Today's Topics:
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>     1. Inverse Square for reflected light (Scott Goelzer)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Wed, 8 Dec 2021 11:34:57 -0500
> From: Scott Goelzer <s.goelzer@comcast.net>
> To: "Phys-L@phys-l.org" <Phys-L@Phys-L.org>
> Subject: [Phys-L] Inverse Square for reflected light
> Message-ID: <A58DE255-DB76-4959-9224-F62CA11132D4@comcast.net>
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> I wanted some opinions or confirmation about some results of an optics experiment some of our freshman devised.
>
> In the first part, students were tasked with proving the inverse square lab using a Pasco light meter and a standard ray box. No problems - reasonable and expected results were obtained by varying the distance.
>
> Student were then asked to devise their own experiments to test inverse square law. Two groups decided to measure the intensity of reflected light from a plane mirror as a function of distance. They were puzzled (as was their teacher) with very linear results. At this time, I believe the groups did a reasonable job taking measurements.
>
> There is surprisingly little about this effect on any physics site, but some photography sites confirm the effect without explanation.
>
> 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.
>
> Any ideas?
>
> Scott
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> Scott Goelzer
> Physics, Engineering, & Chemistry
> Coe-Brown Northwood Academy
> Northwood NH
> sgoelzer@coebrown.org
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