Microscopes and Telescopes
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Vanderjack, Karisa Dwight D. Eisenhower H. S.
1. To use a knowledge of lenses to develop how microscopes and
telescopes were first invented.
2. To apply ray diagrams to explain why these instruments work the
way they do.
1. cheap magnifying glasses -- the kind given away at carnivals
2. various converging and diverging lenses
3. poster board, protractor, markers, and ruler for posters
4. cheap telescopes -- see #1
5. compound microscope and astronomical telescope (optional)
1. As a preliminary stage to my mini-teach, I drew posters containing
the ray diagrams for converging lenses, converging mirrors,
diverging lenses and mirrors, microscopes (simple and compound) and
telescopes (astronomical, Galilean, and Newtonian). I explained
that this lesson comes after the teaching of ray diagrams. I
displayed my posters of the lens and mirror diagrams. Also, I
showed the group an 'air' lens which consists of two watch glasses
epoxied together to appear to be a converging lens. When the lens
is immersed in water (phosphorine added for effect) and a light
shown through the lens, the light actually diverges. This is due
to a smaller index of refraction for air than water. Another neat
idea is to use very large concave and convex mirrors to show
student the pronounced difference in the two. Harry Hasegawa
demonstrated using the large concave mirror to project a real image
on a far wall.
2. To begin, give every student a cheap magnifying glass. Ask
students to explain what it is and what it does. Students will be
able to make real images of the classroom lights on their desks.
Also, they will be able to magnify print, their finger, etc. Then
most students will be able to say this is a converging lens. Refer
to lens diagram for distant objects and objects closer than focal
length. Ask students if there are other instruments which make
objects appear larger. Most will say microscopes and telescopes.
Then ask if the telescope actually makes the moon larger than it
really is. To illustrate the optical principle that far away
objects look smaller than near objects, let students look out the
window, place their hand palm up in front of them, and see if they
can put a car in their palm. Then conclude that the telescope
makes objects appear closer not larger.
3. Now let students 'play' with various combinations of lenses to form
microscopes and telescopes. Pick a distant object to view
(example: the wall clock). Also have books or typed papers to view.
Let students 'play' for about 5 to 10 minutes with lenses and record
their observations. Encourage them to find combinations that have
erect and inverted images.
4. Use posters of ray diagrams to explain why certain lens
combinations have different effects. Use posters of the
microscopes and telescopes in your explanation. Also include
tidbits of information on Anton Van Leeuwenhoek and Galileo Galilei
and their ideas.
5. As an optional activity, have a compound microscope and a nice
telescope for the students to look through and make some qualitative