Lab # _____: Using a Compound Light Microscope
Lab Skills: 6, 8, 13, 23
Background: The microscope is an important scientific tool. It enables a person to observe
things too small to be seen with the unaided eye. A compound microscope has at least two
lenses in it. Light passes through the specimen from a lamp underneath the specimen. The
objective causes the light rays coming from the specimen to spread apart, forming an enlarged
image of the object. The second lens is located in the eyepiece and is referred to as the
ocular. It focuses and further enlarges the image.
Working with a compound light microscope, you may use specimens that have been prepared in one of two ways. A
prepared slide is made to be permanent by science manufacturing companies. A wet mount slide, on the other hand, is
made for temporary use, but can be made by you. During this lab you will gain experience using a microscope properly.
Hypothesis: If the lenses of a microscope magnify an image, then… (tell me what will happen to the appearance of the
specimen observed.)
Procedure:
Part 1 – Learning about the microscope…
1. The proper way to carry a microscope is in
the upright position with one hand holding the
arm and the other supporting the base. You
should always use the microscope away from
the edge of your lab table. Also, check to
make sure that the electrical cord is not
dragging through water or interfering with
your work area in any way.
2. Refresh your memory of the parts of a
microscope. Compare the parts shown in the
diagram to the actual parts of the microscope.
3. Examine the diaphragm. Adjust it to the
largest opening so that the greatest amount
of light possible enters the microscope. Look
through the eyepiece and describe what
happens when you slowly rotate the dial
to the lowest light setting on a sheet of lined paper labeled with each step for which you need to record a
response.
4. Look at the microscope from the side. Slowly turn the coarse adjustment one-half turn clockwise. In which
direction does the stage move?
5. Look at the number followed by an “X” on the side of each objective. This number is the objective’s magnifying
power. The “X” stands for “times.” The number tells how many times an object is magnified by that lens. What
is the magnifying power of the low-power objective?
6. Locate the high-power objective. What is its magnifying power?
7. If the lenses ever look dirty or smudged notify your teacher. Use special lens cleaning towels only because other
kinds can damage the lenses.
8. The eyepiece, or ocular lens, also has a magnifying power. The total magnification of the microscope is
calculated by multiplying the power of the eyepiece by the magnification of the objective. If the power of the
eyepiece is 5X and the objective is 10X, then the total magnification of the image is 5X x 10X = 50X.
9. Examine the eyepiece. What is its magnification?
10. What is the total magnification produced at low power? Show your work.
11. What is the total magnification produced at medium power? Show your work.
12. What is the total magnification produced at high power? Show your work.
Microscope Use Lab
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Part 2 – Preparing and examining a wet mount…
13. Cut a 5-mm square of newsprint with the letter “e” near the center.
14. Place the square in the middle of a clean slide so that you can read it as you normally would. With a pipette, put
2-3 small drops of water on the square.
15. Now carefully drop a clear plastic cover slip onto your slide. Hold the cover slip at about a 45° angle to the slide
and move it toward the drop. As the water touches the cover slip it will
spread along the edge.
16. Make sure that your slide does not contain too many air bubbles in the
water underneath the cover slip. If there are too many then you will
have to start over.
17. Blot off any excess water on the top or bottom of the slide with a paper
towel.
18. Set the slide on the stage so that the “e” is over the hole in the stage in
position so that it can be read normally. Make sure the diaphragm is at the largest opening.
19. Focus the image at low power.
20. Draw exactly what you see through the eyepiece in exactly the same position and at
the same size in a circle about the size as the one shown to the right.
21. Move the slide to the left. Which way does the image move?
22. Move the slide to the right. Which way does the image move?
23. Move the slide downward. Which direction does the image move?
24. Before changing to high power, the specimen must be in sharp focus in the center of the low-power field of view.
All focusing at high power is done with the fine adjustment knobs.
25. Again, but this time at high power, focus the letter “e”. Only a slight turn of the fine adjustment knob will be
needed to do this.
26. As you did for step 20, draw the letter “e” again but this time exactly as you see it at high power.
27. Is the field of vision larger under high power or low power? How do you know?
28. Which field of vision is brighter, high power or low power?
Part 3 – Resolving power and depth of field…
29. Make a wet mount slide using a small square of colored newsprint (approx. 5mm X 5mm).
30. Record the colors of the square as you normally see it with your eyes.
31. Resolving power is the ability to distinguish between two separate points that are very close together.
Microscopes have a resolving power greater than that of the human eye.
32. Observe the slide at low power. Then switch to high power. Examine the light and dark areas of the
square. How is the color distributed and what colors do you see?
33. The depth of field is the distance above the slide in which the object is in good focus.
34. Prepare another wet mount, this time using two hairs of different colors. Cross them on the slide.
35. View the slide at low power. Focus directly on the point where the hairs cross. Are both hairs in focus at low
power?
36. Switch to high power and observe the hairs. Are both hairs in focus at high power? Explain.
37. Prepare wet mounts of other things, such as pieces of cloth, skin, a fly’s wing, or anything that is thin enough for
light to pass through it. Sketch the things that you observe under the microscope. Label each drawing with
its name and the magnification used. Your data for this step should resemble the boxes shown on the
top of page 3 of this lab handout. You will need to draw your pictures in the results section of your lab
report.
Microscope Use Lab
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1
Specimen 1 name:
______________________
2
Magnification: _________
Specimen 2 name:
______________________
Magnification: _________
3
Specimen 3 name:
______________________
4
Magnification: _________
Specimen 4 name:
______________________
Magnification: _________
38. As soon as you are done using the microscope you should turn off the lamp, unplug the microscope, and return
the objective to low power.
Analysis:
A. Why should you make sure that a wet mount slide does not have air bubbles?
B. Besides magnifying it, what did the microscope do to the image of the letter “e”?
C. What is the resolution or resolving power of a microscope?
D. Is a microscope’s resolving power greater under low power or high power?
E. Using the concept of resolving power, explain why the color of the newsprint looked different when you looked at it
under the microscope.
F. What is depth of field?
G. Is the depth of field greatest under low power or high power?
H. If you were quickly scanning a slide to find a certain type of organelle, which
objective would be the best one to use? Why?
Microscope Use Lab
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Name(s) ______________________________________________________________________________________
1
Specimen 1 name:
______________________
2
Magnification: _________
Specimen 2 name:
______________________
Magnification: _________
3
Specimen 3 name:
______________________
4
Magnification: _________
Specimen 4 name:
______________________
Magnification: _________
Name(s) ______________________________________________________________________________________
1
Specimen 1 name:
______________________
2
Magnification: _________
Specimen 2 name:
______________________
Magnification: _________
3
Specimen 3 name:
______________________
4
Magnification: _________
Specimen 4 name:
______________________
Magnification: _________
Microscope Use Lab
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