Chapter 3: The Microscope

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The microscope slide rests on the _______ while being viewed.

a. base

b. condenser

c. iris

d. stage

d. stage


Your lab microscope is parfocal. What does this mean?

a. The specimen is clearly in focus at this depth.

b. The slide should be almost in focus when changing to higher magnifications.

c. You can easily discriminate two close objects as separate.

b. The slide should be almost in focus when changing to higher magnifications.


If the ocular lens magnifies a specimen 10X, and the objective lens used magnifies the specimen 35X, what is the total mangification being used to observe the specimen?

10X x 35X = 350X


How do you clean the lenses of your microscope?

a. with a paper towel

b. with soap and water

c. with special lens paper and cleaner

c. with special lens paper and cleaner



You should always begin observation of specimens with the oil immersion lens.

False. You should always begin with the scanning objective lens.


Explain the proper technique for transporting the microscope.

Carry it upright with one hand supporting the base and one holding the arm.



The microscope lens may be cleaned with any soft tissue.




The microscope should be stored with the oil-immersion lens in position over the stage.




When beginning to focus, use the lowest-power lens.




When focusing on high-power, always use the coarse adjustment knob to focus.




A coverslip should always be used with wet mounts.



What part of the microscope is the:

platform on which the slide rests for viewing?



What part of the microscope is:

used to adjust the amount of light passing through the specimen?

iris diaphragm lever


What part of the microscope:

controls the movement of the slide on the stage?

mechanical stage


What part of the microscope is:

delivers a concentrated beam of light to the specimen?



What part of the microscope is:

used for precise focusing once initial focusing has been done?

fine adjustment knob


What part of the microscope:

carries the objective lenses; rotates so that the different objective lenses can be brought into position over the specimen?



Define virtual image.

The image generated by the ocular lens after it magnifies the real image created by the objective lens.


Define resolution.

The ability to discriminate two close objects as separate.


The distance from the bottom of the objective lens to the surface of the slide is called _______.

working distance


Assume there is an object on the left side of the field that you want to bring to the center (that is toward the apparent right). In what direction would you move your slide?



The area of the slide seen when looking through the microscope is the ______.



If a microscope has a 10X ocular lens and the total magnification at a particular time is 950X, the objective lens in use at that time is _____.



Why should the light be dimmed when looking at living (nearly transparent) cells?

to increase contrast


If, after focusing in low power, you need to use only the fine adjustment to focus the specimen at the higher powers, the microscope is said to be _____.



You are using a 10X ocular and 15X objective, and the field diameter is 1.5 mm. The approximate field size with a 30X objective is _______mm.

0.75 mm


If the diameter of the high-power field is 1.2 mm, an object that occupies approximately a third of that field has an estimated diameter of ______mm.

0.4 mm


Say you are observing an object in the low-power field. When you switch to high power, it is no longer in your field of view. Why might this occur?

What should you do initially to prevent this from happening?

Moving to a higher power lens narrows the field of view, and the object could be outside of the new field of view if it was not perfectly centered under the lower powered lens.

Center the object being viewed before switching to a higher powered lens.


Does the following factor increase or decrease as one moves to higher magnifications with the microscope?


increases within limits


Does the following factor increase or decrease as one moves to higher magnifications with the microscope?

working distance



Does the following factor increase or decrease as one moves to higher magnifications with the microscope?

amount of light needed



Does the following factor increase or decrease as one moves to higher magnifications with the microscope?

depth of field



A student has the high-power lens in position and appears to be intently observing the specimen. The instructor, noting a working distance of about 1 cm, knows the student isn't actually seeing the specimen. How so?

The working distance for the high-power lens should be much smaller - about 0.5 mm, so the whatever the student is observing is not in focus.


Describe the proper procedure for preparing a wet mount.

Place a drop of water or saline on a clean slide. Place the object/sample in the drop of water. Hold a cover sip at a 45 degree angle at on side of the drop and slowly lower the coverslip.


Indicate the probable cause of the following situation during use of a microscope.

Only half of the field is illuminated.

Something is blocking the light path.


Indicate the probable cause of the following situation during use of a microscope.

The visible field does not change as the mechanical stage is moved.

The slide could be stuck to the lens or the working distance could be too great and not properly focused.

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