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On Tue, 09 Apr 2002 17:00:11 -0700 "Daniel L. MacIsaac"
<Dan.MacIsaac@NAU.EDU> writes:
> ...I frequently get odd requests from web-surfers who stumble across > PHYS-L and its archives. Yesterday I got a request from a surfer who was > looking for a nice explanation of the optics of a standard rear-view automobile mirror, which when tilted significantly dims the reflected image. > > I think I know how the mirror works; I THINK it's a glass wedge and > by controlling the incident angles one can reflect light multiple > times within the wedge, attenuating it. I could easily be very wrong. > But I can't find a simple explanation of the design on the web anywheres. Can > anyone help steer me to an appropriate online explanation? > You are correct about the rear view mirror being wedge shape. As you know, there are two reflections fom all rear surface glass silvered glassz mirrors. the first reflection ( a comparatively weak one) comes from the front of the mirror at the air-glass interface. Then a stronger reflection comes from the back of the mirror at the GLASS-"SILVER" interface. When these
two reflections reach our eyes, they are very close together and it is difficult
to perceive the weaker one at the initial air-glass interface . However,
if the mirror is wedge shape. The weak reflection from the air-glass surface and
the stronger rfeflection from the back of the mirror are much further
apart. So we can tilt the mirror to either receive the weak reflection from the
front surface OR we can tilt it to receive the stronger reflection from the rear
surface.
Herb Gottlieb from New York City
(Where our police stations have one way mirrors on the walls
of their interrogation rooms)
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