Microscopes and Telescopes

Vanderjack, Karisa                   Dwight D. Eisenhower H. S.
                                     597-6300
                           

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.