Did you think of a question that could be studied, or make an observation
that was interesting or unexpected? You should send it to the Question
board!
Discuss some of these questions with the people in your group:
My friend Bob is 213 cm (7 feet) tall. He wants to hang a mirror on the wall so that
standing 3 meters away from it he will be able to see all of himself
-- cowboy boots to cowlick. None of the mirrors in the catalog are 213 cm tall,
and some of the prettiest are rather smaller. Draw some pictures showing how
light travels from his toes to his eyes, to determine
exactly how high above the floor the bottom edge of the mirror can be, and still
be able to see them. If he is standing a different distance from the mirror,
will the answer change a lot, a little, or not at all?
Tape a piece of paper to a table, and stand a mirror vertically somewhere
in the middle of it (this time it works better to have the mirror in the
"billboard" orientation). Place some small object at one corner of the
piece of paper, where you can see it in the mirror if you look from the
right direction. Draw a straight line on the paper between your eye and
the mirror that seems to be aimed at the object that is seen in the mirror.
Now move yourself a little bit, to where the object is just visible at
one edge of the mirror, and draw another line aimed at the object; and
then move again so that the object is seen at the other edge of the mirror
and draw a third line. Now remove the mirror (marking on the paper where
it had been), and extend the three lines you drew until they cross. The
crossing points are the apparent position of the image (the object seen
in the mirror). Where was the image, and how is it related to the actual
position of the object?
Why was it recommended that the mirror used with the light beam be arranged
in the taller orientation (like a door, instead of a billboard)? What kind
of problem arises with the other orientation (especially when the mirror
is close to the slot)?
Why is it important that the mirror used with the light beam be vertical
(perpendicular to the table top), and not tilted forwards or backwards?
What problems arise in each case?
Sometimes when you look out the airplane window, you see bright flashes
of light from the ground, caused by swimming pools, rivers, and puddles.
The places where the flashes occur seem to move along with the airplane.
What are the conditions (time of day, direction you are looking) that lead
to this effect?
These discussion questions are a bit open-ended, and some people find them
very confusing. We have provided
some examples of good and bad discussions on a
separate page.
Please send
us your discussion of either Question 1 or Question 2, and discussions
of two other questions.
Don't forget to tell us who is in the group.
If there is something that you don't understand about mirrors, Ask
us!
This is the end of this section.
Please note that these activities are written up (in slightly different
form) and expanded upon in the manual (in
the Mirrors and Light Beams sections). We particularly want to bring to
your attention the activities Making A Periscope, Corner Mirror, and Pieces
of a Circle in the Mirrors section of the manual.