| Chronology | Current Month | Current Thread | Current Date |
| [Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
The distance between source and sensor for light reflected from a clean plane mirror is measured as the sum of the distance from source to mirror, and the distance from mirror surface to sensor, both rays at the same vertical angle to the mirror perpendicular.
Students may not be correctly assessing distance for a reflected light ray.
On Dec 9, 2021, at 11:40 AM, Brian Whatcott <betwys1@sbcglobal.net> wrote:
A ray box provides a well defined ray, narrow in one axis typically the vertical axis and wide in the second orthogonal axis typically the horizontal axis, so that the ray box has no need for critical positioning in more than one axis.
A pasco light meter may have a choice of point or ambient light measuring capability.
An evenly illuminated field has zero light intensity variation with distance in its bounds; a line source has inverse distance light intensity, and a point source has inverse distance squared luminance
The distance between source and sensor for light reflected from a clean plane mirror is measured as the sum of the distance from source to mirror, and the distance from mirror surface to sensor, both rays at the same vertical angle to the mirror perpendicular.
A ray box may be arranged as a line source.
A spot photometer may be arranged to provide an increasing light intensity reading with distance from a line source.Students may not be correctly assessing distance for a reflected light ray.
I think one or more of these factors is responsible.
Brian
-
- From: Scott Goelzer <s.goelzer@comcast.net <mailto:s.goelzer@comcast.net>>
- Date: Wed, 8 Dec 2021 11:34:57 -0500
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
Forum for Physics Educators
Phys-l@mail.phys-l.org <mailto:Phys-l@mail.phys-l.org>
https://www.phys-l.org/mailman/listinfo/phys-l <https://www.phys-l.org/mailman/listinfo/phys-l>