Tools of Magnification
How Could We Obtain More Magnification?
Students now have observed newsprint and other materials using a hand magnifier and a drop of water. Ask students, What could we use to magnify the materials further?
Each group of students should have access to a microscope. Allow each group to examine its microscope for a few minutes. Then ask students to locate basic parts as you name and describe the function of each one (eyepiece, arm, stage, lenses, light source, etc.). Tell students, The stage is the part of the microscope that holds a slide. It is similar to a stage for a performance. Can you find it?
It is important for students to notice that the microscope has more than one lens. This is why we call it a "compound" microscope. Be sure students notice the curvature of each lens. Help students relate the lens shape to the observations they made about the water drop and hand lens used earlier in the activity.
The sides of the eyepiece and objectives containing the lenses are marked with a number and the letter "x." Ask students what "x" usually means in mathematics (multiplication or times). This would be a good time to explain how the total magnification is calculated for a compound microscope.
Point out that a microscope's magnification rating is determined by multiplying (not adding, as some students may guess) the power of the top lens (on the eyepiece) by the power of the bottom lens (on the objective being used). For example, a microscope with an eyepiece of 10x and an objective of 4x will magnify an image 40 times (10 x 4 = 40). You may wish to ask students how the compound microscope and the hand lens compare.
Have students use "The Compound Microscope" student sheet to find to review the microscope parts and functions you have discussed as a class. Also, have students locate components not yet mentioned so far. You may have a microscope with a condenser to intensify the light, for example, and/or a microscope with a diaphragm aperture to adjust the amount of light passing from the light source up through the object. Discuss the importance of each part.
- Moreno, N., Tharp, B., Erdmann, D., Rahmati Clayton, S., Denk, J. (2008). The Science of Microbes Teacher’s Guide. Houston, TX: BioEd.
- Caprette, D. (2005). Light microscopy: Instrumentation and principles. BioEd Online. Baylor College of Medicine: Houston, TX.
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Grant Number: 5R25RR018605