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Re: Double concave mirror toy



The commercial Mirage is one of our most popular exhibits. The black flying
saucer shaped double mirror is hidden inside a plywood box. The hole in the
top mirror is immediately below a similar hole in the box top. A thin sheet
of Plexiglas covers this hole to prevent small hands from entering.

We use to have a quarter at the object position and our sign said that if
the visitor could pick up the quarter at the top (the real image), he could
keep it. After a year of that we put the original pink plastic pig in the
object position and we now offer a free lifetime Science Place membership to
anyone who can pick up the pig.

We also have a small flashlight attached to the table with a thin cable.
When the visitor shines the light on the image pig at the top, he sees
"specular reflections" from the pig just as if it were a real object.
Obviously, the rays from the flashlight pass through the real image and
reflect from the two mirrors and from the object pig just as the rays from
the ceiling lights do to create the image pig.

The real image looks so "real" that, even with a well-drawn ray tracing
diagram, we sometimes have difficulty convincing visitors that it's not
magic.

Paul O. Johnson
Exhibit Developer
The Science Place
Dallas Texas

----- Original Message -----
From: "Scott Goelzer" <sgoelzer@EARTHLINK.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, May 07, 2002 2:00 PM
Subject: Re: Double concave mirror toy


Wow, so many questions:
best to see it for yourself (worth 40$)

My observations:
When the image of the pink pig supplied with the demo is visible above the
hole in the top of the clam shell mirrors, a pen laser is aim directly at
the image. The result is that the laser appears to illuminate the image as
if the pig were actually there. With clean mirrors, it is most convincing.
I have not measured exact angles, but I would estimate that viewing (and
illumintating ) between 30 to 60 degrees produces the best results.
Looking
down the hole at the pig while someone else is holding the laser and
viewing
the illusion make it very easy to envision the light path.

Apologies to Tom if I said too much (or little)

Scott


*****************************
S.Goelzer
Physics Teacher
Coe - Brown Northwood Academy
Northwood NH 03261
603-942-5531 ext43
sgoelzer@coebrownacademy.com
*****************************



on 5/7/02 2:38 PM, Ludwik Kowalski at kowalskiL@MAIL.MONTCLAIR.EDU wrote:

Tell us more about this. The real image of what? How
was that image produced? The real image where (or on
what)? Was the reflected beam only a tiny fraction of
the incident beam or was it a big fraction? How was
the incident laser beam directed with respect to rays
making the real image? How was the reflected beam
directed? What happens when the real image becomes
fuzzy? Does the reflected beam disappear when the
light producing the real image is turned off?
Ludwik Kowalski

Scott Goelzer wrote:

Just did this! How cool. Took most everyone in the department by
surprise.

Try shining a laser pointer on the real image. Ask students why
something
you can't touch seems to reflect light.

Tom Bross