Using the Microscope Purpose: To become familiar with the parts and operation of the compound microscope and to learn how to prepare and observe wet mount slides. Materials: microscope pipette Clean slide scissors Cover slip magazine picture Lens paper hair of two different people Paper towel ruler Newsprint water Dissecting probe Procedure: Follow all procedure statements which are interspersed with the observations questions in the next section. Observation questions are lettered. Observations: Part 1 – Learning about the microscope ¾ Obtain a microscope from your teacher. Carry it with one hand holding the arm and the other hand supporting the base. Plug in your microscope and turn on the light source. ¾ Locate the diaphragm underneath the stage. Adjust it to the largest opening so that the maximum amount of light enters the microscope. Look through the ocular lens when you are adjusting the diaphragm to see the effect of the different amounts of light. ¾ Carefully rotate the revolving nosepiece. You can hear and feel it click as an objective is snapped into place. It contains three objective lenses, each with a different magnifying power. There is a low power, medium power and a high power objective lens. ¾ Locate the low power objective lens. It is the smallest objective on the nosepiece. The magnifying power for each objective is engraved on its side. This tells you how many times that particular lens magnifies an object. a) What is the magnifying power of the low power objective lens? b) What is the magnifying power of the medium power objective lens? c) What is the magnifying power of the high power objective lens? ¾ Locate the ocular lens. This lens if found in eyepiece tube. This also has a magnifying power. d) What is the magnifying power of the ocular lens? ¾ The total magnification of the microscope can be calculated by simply multiplying the magnification of the ocular lens by the magnification of the objective lens being used. For example, if the ocular lens was 15X and the objective lens being used was 10X, the total magnification being used is 15 x 10 = 150X. e) What is the total magnification power when the low power objective is being used? f) What is the total magnification power when the medium power objective is being used? g) What is the total magnification power when the high power objective is being used? ¾ Locate and carefully move the coarse adjustment knob and observe the movement it produces. h) Which part of the microscope moves when you turn the coarse adjustment? ¾ Turn the fine adjustment knob and closely observe the movement it produces. This motion may be difficult to see. i) How do the effects of the coarse and fine adjustments differ? PART 2 – Preparing and examining a wet mount. ¾ Using a pipette, put one drop of water on the slide. ¾ Find a small letter “e” in some newsprint and cut it out. Place the “e” in the middle of a clean slide right side up. ¾ Now cover the specimen with a clean cover slip. Hold the cover slip at a 45⁰ angle to the slide and gently lower the cover slip into place. Use the end of your pencil or your little finger to gently tap out any bubbles. ¾ Place the slide on the stage and click the low power objective into place. Using the mechanical stage, move the slide to the left. a) As you look through the ocular lens, which way does the image move? ¾ Move the slide to the right. b) Now as you look through the ocular lens, which way does the image appear to move? ¾ Move the slide away from you. c) As you look through the ocular lens, which way does the image move? ¾ Look through the ocular lens and change the diaphragm to observe each of its settings. d) What does the diaphragm control? ¾ Before using the medium or high power objective, the specimen must be focused in the center of your field of view. Change to the medium power objective and focus the letter “e”. Now switch to high power. All focusing under high power is done only with the fine adjustment knob. e) Is the field of view (area seen) larger under high power or low power? f) Compare the brightness of the field under high power and low power. DIAGRAM: Draw the letter “e” under as seen under low power. Label : dark
ink, plain newsprint. (Remember to look at your diagram guideline sheet from
your binder for guidance in drawing.)
PART 3 – Resolving Power and Depth of Field ¾ Make a wet mount using a 1 cm square piece of colored magazine print. Try to choose a square that has both light and dark tones but try to avoid black. a) What are the colors of the square that are seen with the naked eye? ¾ 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. Observe the slide under low power then switch to high power. b) How is the color distributed? (pattern) c) What colors do you see under high power? ¾ Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus under the microscope. Prepare another wet mount slide, this time of two hairs of different colors. Add your drop of water and then cross the two hairs on the slide. Add your cover slip. Place the slide on the microscope and using the low power objective, focus directly on the point where the hairs cross. d) Are both hairs in focus on low power? e) Switch to high power. Are both hairs in focus at the same time under high power? Explain. the hairs
high power. Label : outer edge, DIAGRAM:
Draw
as seen
under
center shaft
CONCLUSION: Proper use of the microscope has been studied. Answer the following concluding questions: 1. Why should a wet mount not have any bubbles? 2. What did the microscope do to the image of the letter “e”? 3. Why must you center and focus the object in the field of view under low power before switching to high power? 4. Why is only fine adjustment used for high power? 5. Explain why the color of the magazine picture looked different when you looked at it under the microscope. 6. By using the idea of depth of field, how can you tell which hair was above the other? 7. If you were scanning a slide to find a particular area, which objective lens would be better to use?