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What kinds of mirrors can I use to make a periscope?
You need two small mirrors, but they don't have to be identical.
If you have a rectangular mirror, or one with a handle, it's okay if part
of it sticks out the side of the carton. If your mirror is round, like the
mirror in a make-up compact, you may want to tape or glue it to a square
of cardboard before inserting it into the slot in the milk carton. If you
have a mirror with a magnifying side and a nonmagnifying side, have the
nonmagnifying side facing the hole.
To make a periscope from a 1-quart milk carton, your mirrors
must be smaller than 31/2 inches in at least one dimension. If the only
mirrors you can find are larger than that, you can use half-gallon milk
cartons instead.
What if I want to use half-gallon milk cartons or some
other boxes?
When you are making a periscope, it's important to make
sure that your mirror is positioned at a 45-degree angle. If you use a wider
milk carton or some other box, just measure how wide your box is. Then measure
that same distance up the side of the box and make a mark. The line between
your mark and the opposite corner of the box will be at 45 degrees.
How does my
periscope work?
Light always reflects away from a mirror at the same angle
that it hits the mirror. In your periscope, light hits the top mirror at
a 45-degree angle and reflects away at the same angle, which bounces it
down to the bottom mirror. That reflected light hits the second mirror at
a 45-degree angle and reflects away at the same angle, right into your eye.
Can I make a periscope with a really long tube?
You can make your peri- scope longer, but the longer the
tube is, the smaller the image you'll see. Periscopes in tanks and submarines
have magnifying lenses between the mirrors to make the reflected image bigger.
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Use the knife to cut around the top of each milk
carton, removing the peaked "roof."
Cut a hole
at the bottom of the front of one milk carton. Leave about 1/4 inch of carton
on each side of the hole.
Put the carton on its side and turn it so the
hole you just cut is facing to your right. On the side that's facing up,
measure 2 3/4 inches up the left edge of the carton, and use the pencil
to make a
mark
there. Now, use your ruler to draw a diagonal line from the bottom right
corner to the mark you made.
Slide the mirror through the slot so the reflecting
side faces the hole in the front of the carton. Tape the mirror loosely
in place.
Hold the carton up to your eye and look through
the hole that you cut. You should see your ceiling through the top of the
carton. If what you see looks tilted, adjust the mirror and tape it again.
Repeat steps 2 through 6 with the second milk
carton.
Starting at the bottom right corner, cut on that
line. Don't cut all the way to the left edge of the carton-just make the
cut as long as one side of your mirror. If your mirror is thick, widen the
cut to fit.
Stand one carton up on a table, with the hole facing you. Place
the other carton upside-down, with the mirror on the top and the hole facing
away from you.
Use your hand to pinch the open end of the upside-down
carton just enough for it to slide into the other carton. Tape the two cartons
together
Now you have a periscope! If
you look through the bottom hole, you can see over fences that are taller
than you. If you look through the top hole, you can see under tables. If
you hold it sideways, you can see around corners.
