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 these questions with the people in
your group:
If you wear glasses, compare their behavior to the lenses we have studied.
Borrow everyone else's glasses, too!
You will find that both positive and
negative lenses are common; more rarely, you will find astigmatic lenses,
that stretch things in some direction (this is most clearly revealed if
you turn the glasses while looking through them).
And of course, some lucky people
have several lenses in the same set of glasses.
Make a table that classifies the lenses you
find, and compare them to the lenses in the kit.
You might also have a column in the table listing
the purpose for the glasses (i.e. wearer is nearsighted,
reading glasses, driving glasses, etc.).
Classify the lenses in the kit in the following ways, making a table of
the results
Hold each lens close to your eye and look at some small object -- you will
have to find the right place to hold the object, to see it most clearly.
Keep the lens close to your eye and classify
each lens according to its magnifying ability; also note how far away you
have to hold the object being observed so
that you can see it clearly.
Another way to use a lens as a magnifier is to hold it near to the object
being studied (which might be at arm's length) -- again, there is a right
distance between lens and object. Classify each lens when used this
way.
Now look at a distant object through each lens, holding it close to your
eye, and classify each lens on how it performs (mostly the answer will
be "Too fuzzy for comfortable viewing," and all you will get from
long study of what you see is an eyestrain headache.
But do notice whether the
fuzzy blob looks bigger or smaller
than usual, and whether it is different in any other way).
Finally, look at the distant object through each lens, holding the lens
away from your face -- arm's length, or a bit closer.
Again classify each
lens.
Most of the lenses magnify, and do other similar things; these are the
positive lenses.
We have also included a negative lens, which
does not magnify, no matter how you use it.
Describe a possible use for
a negative lens.
Compare the magnifying ability of a glass vial filled with water to a glass
vial filled with salad oil or rubbing alcohol; a solid cylindrical rod
of glass or plastic might also be interesting to study. Are all of these
lenses positive? Which is the strongest magnifier?
Please send
us your discussion of two of these questions. Don't forget to
tell us who is in the group.
If there is something that you don't understand about lenses, Ask
us! This is the end of this section.
Please note that these activities are written up (in slightly different
form) in the manual (in the Lenses and Light Beams sections).
The next section is about curved mirrors