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Re: Spherical Mirrors



Even if the focusing and "gate" problems were "solved"
in a mind experiment, would not the interior fade to
black due to less than perfect photon re-emission on
each successive reflection ? John Barrere

--- Jennifer S <jmsphys@JUNO.COM> wrote:
In the course of our classroom (high school)
discussion about concave
mirrors one of my students posed the following
question about a
reflective sphere. Suppose you have a sphere with a
small hole in it.
The inside surface is reflective. If light passes
into the sphere, would
it be possible to "trap" any and all light inside
the sphere? Of course,
this is assuming that ALL wavelengths of light are
reflected to the SAME
focal point.

We talked about the fact that parallel rays hitting
the surface of a
concave mirror will be reflected to the focal point
(F), halfway between
the suface of the mirror and the center of curvature
(C). Since the
concave mirror is part of a sphere just assume that
the entire sphere
exists. If parallel rays enter through the hole
they will travel to the
other side of the sphere at which point they will
hit the reflective
surface and pass through F. If we choose any light
ray and follow its
path AFTER passing through F, will it continue until
it hits the "next"
reflective surface and then pass through a focus, F'
which lies on a
"new" principal axis? (That is, the principal axis
of this "next"
reflective surface?) If so, would this process
repeat and actually
"trap" light inside the sphere?

If there are flaws in my reasoning, please correct
me (gently!) Thanks.

Jennifer




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