Tuesday, February 7, 2012

Teaching About the Microscope

We require Microscope Licenses (which have to be renewed every year) for a child to independently use the microscope. Edmund Scientific has the nicest selection of slides that I've found, with sturdy storage cases and helpful identification booklets for each set. They also sell plain glass slides and coverslips for those who want to make their own.

The first step in getting your microscope license is a background lesson on microscopes and an explanation of the parts of the microscope. We have students complete a blank diagram by way of note taking. Then a different diagram is given to them to complete (using a word bank) as part 1 of the test. They are not allowed to look at their notes when they take it.

The second step is to have a one-on-one lesson on removing a slide from the storage box, placing it on the stage, securing it with the stage clips, focusing, drawing the slide, removing and replacing it. We have special paper that the children draw their observations on. Part 2 of the test consists of the child choosing, focusing, sketching, and putting away a slide while the adult observes them. If they are successful and show that they can respect and care for the equipment, we issue a small paper license which goes in their work folders. It is a BIG DEAL because it is the only Test we give all year.

Here is the lesson I've developed to introduce the Microscope:

I use the (now sadly out of print) book It's Fun to Know Why: Experiments with Things Around Us by Julius Schwartz and illustrated by Edwin Herron. Published by McGraw-Hill in 1952. The chapter "Glass -- A Window on the World" is perfect. However, you could easily make up your own text to explain. First, glass is made from sand. Second, glass is made in three ways: blown, pressed, and rolled. Third: mirrors have a silver backing to reflect light. Fourth: lenses and the discovery of Leewenhoek of a microscopic world in a drop of pond water.

If you can find this old book, though, it's really wonderful. There are also chapters on Iron, Coal, Cement, Rubber, Wool, Salt, Bread, Soap, and Paper.

The hands-on demonstrations are these

Demonstration 1:
black construction paper
magnifying glass

Have the children look at plain beach sand on a piece of black construction paper with the hand lens to see the small clear grains that sparkle like glass. There may also be grains of other colors.

Demonstration 2:

Have the children look at themselves in mirrors. Plain mirrors with silver on the back are best (craft stores like Michael's or Edmund Scientific).

Demonstration 3:
water in a glass

Demonstrate that it is the curve that magnifies. Tear a small piece of newspaper and set it on a plate. Rub a dime-sized thin layer of Crisco over a section of the print. Put your finger in a glass of water and carefully drop a single drop of water onto the greased section. If the water lands and makes a bubble, it should magnify that area.

Also try taking an ungreased piece of newspaper on a different plate and just pour a layer of water on top of the whole piece of paper. When the water is flat it will not magnify. This proves that it was the Curve and not the Water that did the magnifying.

Demonstration 4:
bag of lenses

A mixed bag of lenses that can be combined in different ways is fun for exploration.

Demonstration 4 comes in the part of the book that explains Leewenhoek's discoveries.

While students are exploring with the lenses, I like to read a section from The Evolution of Calpurnia Tate, Newbery honor book from 2010. From pages 102 to 106, she describes her experience in 1899 of looking through her grandfather's microscope and seeing the world of invisible creatures in the pond water.

A nice follow-up book for further student exploration would be A World of Microorganisms. Call number 579

After hearing about Calpurnia's experience with the old bronze microscope, it is good to move into a discussion of the parts of the microscope. Instead of using a reflector to capture and focus sunlight, we plug the microscope in and the light source comes on. Some parts of the microscope are still the same, like the focus knob and the eye piece.

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