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naive ideas: Light



Since nobody commented on my quibbles with the "Forces and Motion" section,
I'll assume there is 100% agreement with what I wrote (tongue firmly in
cheek).

many of the items, aren't exactly misconceptions as much as imprecise
statements; e.g. in the Forces and Fluids statement, item #1 states "Objects
float in water because they are lighter than water". This is correct if you
interpret "lighter" to mean less dense. This is the only interpretation of
"lighter" that makes sense in the construct of the sentence. Since no
quantity of water was given. In other words if it said "lighter" than a
litre of water we would have a genuine statement of a misconception.

Light:

2. An object is "seen" because light shines on it. Light is a necessary
condition for seeing an object an eye.

I think this is basically correct. Light is a necessary condition for my
eye to see an object. Light must be shining on the object that I am trying
to see. For if it were not, there would be no scattering of the light into
my eye.

5. Light is not necessarily conserved. It may disappear or be intensified.

This is correct. Photon number is not a conserved quantity. The purpose of
photo-multiplication tubes, lasers etc is to intensify the light in the
instrument. The purpose of sunglasses is to diminish the light going
through them.

19. Students will often think about how a lens forms an image of a
self-luminous object in the following way. They envision that a "potential
image" which carries information about the object leaves the self-luminous
object and travels through the space to the lens. When passing throught the
lens, the "potential image" is turned upside down and may be changed in
size.

One way of viewing an optical system is to view each optical element of the
system producing a transform on the information that goes through, "a
transform function"; the above strikes me as a fair description of what a
transform function of a particular optical element produces.

Joel Rauber
rauberj@mg.sdstate.edu