Microscopes and Telescopes

Vanderjack, Karisa Dwight D. Eisenhower H. S.

Objectives: 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. Apparatus Needed: 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) Recommended Strategy: 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 observations.
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