The Reflection Property of an Ellipse
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This animation demonstrates the reflection property of ellipses.
(See notes below.)
A light pulse emitted from one focus of an ellipse is reflected by the ellipse to
its other focus. Because every photon travels exactly the same distance
(see
Tracing Out An Ellipse
and
Tracing an Ellipse with Quetelet and Dandelin),
they all arrive at the other focus simultaneously. But note the change in
density. The pulse is emitted from the left focus
with uniform density; it arrives at the right focus with very
non-uniform density. (11/16/07)