Measuring with a Microscope
Purpose: To learn how to measure the size of microscopic structures and organisms using the microscope to make estimations.
Instructions:
1. Get a microscope and a thin, metric ruler.
2. Place the ruler on the stage, so that when it is viewed it takes up half of your field of vision.
3. Move the ruler so that one of the millimeter lines rests along the right hand edge of your field of vision, with half of the line in view; half out of view.
4. A millimeter is the measurement from the midpoint of a line to the midpoint of the next line. Under the 10X lens, How many millimeters across is the field of vision?(estimate to the nearest tenth of a millimeter if not to the whole millimeter)
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5. Microscopic organisms are measured in units of Micrometers (µm), which are 1,000th of a millimeter. Convert the field of vision to micrometers by multiplying the millimeters by 1,000. How many micrometers across is the 10X (100x total magnification) field?
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6. Viewing the ruler under high power is difficult, and so determining what the micrometer measurement is for high power must be determined mathematically. The equation to do so is:
High power field diameterLow power magnification
------= ------
Low power field diameterHigh power magnification
7. Substitute the numbers you know into the equation and figure out the high power diameter. Show math in the space below:
8. How many millimeters across is the high power field?
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9. How many micrometers across is the high power field?
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Practice Procedures:
When examining objects under the microscope you will have to estimate their size based on the knowledge you have about the diameter of your field of vision. Follow the instructions below and draw a picture of what you see. Label your illustrations with the objects name, magnification and estimated size (in µm)
Examine samples of Paramecium and Mites under low power and estimate their size.
Paramecium= ______
Mites= ______
Examine a cross section of a plant leaf. On the outer surface are small, thin walled cells called epidermal cells. How many epidermal cells would fit across the diameter of the low power field?
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10. To calculate the size of a epidermal cell, divide the field diameter by the number of cells across the field. What is the average size (estimate) of a pith cell?
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11. Now examine the epidermal cells and repeat the above steps to determine the size of the cells under high power. What is the average size of the epidermal cells under high power?
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12. Are your answers to #10 and #11 the same, or close to the same?
13. Should #10 and #11 be the same? Why?