Exercise 2: Use of the Microscope
The ocular lens has a magnification power of
10
All of the following are correct steps in focusing on a specimen under the microscope EXCEPT which statement?
Start with a high power objective lens when focusing.
As the magnification __________, the field diameter ___________.
increases; decreases
If a student is using the 40X lens, what is the total magnification of the image being viewed?
400X If the 40X objective was being used, the total magnification would be 400X. (10 x 40 = 400).
If the field diameter is 8mm and an object occupies one-half of the field, the object is approximately ______wide.
4mm
To best control the magnification of the microscope
Always use low magnification during your initial observation. To examine part of the specimen at higher magnification, move that part of the slide to the center over the aperture before changing to a higher-magnification lens. Use a drop of immersion oil to look at the specimen under the highest magnification.
Viewing the slide with the layered colored threads demonstrated that _____.
At higher magnification less of the slide is visible in the field of view The focal plane is thinner at higher magnification Depth of field is greatest at low power Each thread layer comes into focus separately because the specimen is three-dimensional (it has thickness) By moving the fine adjustment knob back and forth, the layers of the specimen will come in and out of focus
What must be done when using a microscope
Carry the microscope with two hands, one on the arm and the other on the base. Completely unwrap the electrical cord before plugging in the microscope. Store the microscope with the cord wrapped neatly around the base, with the lowest power lens in position. Store the microscope with the low-power objective lens in position. Checking the position of the condenser
The amount of a specimen that is in focus at any given time is called the __________.
Depth of field
If the field of view is too bright, the light intensity can be lowered by turning the fine adjustment knob. (T/F)
False
At higher magnification the light intensity should be decreased so that the image will have good contrast. (T/F) (Why/Why Not)
False - at higher magnifications the amount of light should be increased to adjust the brightness allowing for good contrast and no glare.
Upon initial observation of a specimen, it is best to start with the highest magnification lens in place. (T/F) (Why / Why Not)
False - it is easiest to initially focus using the lowest power magnification as a large portion of the specimen will be in the field of view.
The body tube is the broad flat portion that supports the microscope. (T/F) (Why / Why Not)
False - the body tube supports the ocular lenses.
The ocular lenses are mounted to the nose piece and have variable magnifications. (T/F) (Why / Why Not)
False - the ocular lenses are mounted to the body tube and typically magnify the image ten times (10X).
What are the two ways the brightness or light intensity can be lowered
First, the iris diaphragm creates an aperture that regulates the amount of light passing through the condenser and ultimately the ocular lenses. Second, the amount of light emitted from the light source can be adjusted by turning the illumination intensity control typically located near the on/off switch on a microscope.
If a paramecium appears to be moving to the left in the microscopic field of view, which way should you move your slide to keep it in view?
Left The image through the microscopic view is opposite of the real image being emitted. to keep the specimen in the field of view, the mechanical stage should be moved to the left.
The following are all procedures to measure the field diameter EXCEPT which statement?
Position the slide so that the horizontal line on the paper is on the top of the field.
Which of the following terms refers to the ability of a lens to clearly distinguish adjacent objects as separate?
Resolution
Why should you never clean the microscope with any soft cloth or tissue and water.
The lenses should only be cleaned with lens paper and lens cleaner.
All of the following are ways to best control the magnification of the microscope EXCEPT which statement?
To examine part of the specimen at higher magnification, move that part of the specimen off to the side.
When using the fine adjustment knob to focus, the lens will move either closer to or farther away from the slide, thus causing the focal plane to move through the specimen layers. (T/F)
True
When preparing a wet-mount it is important to cover the specimen with a cover slip to ensure that the objective lenses remain dry. (T/F) (Why/Why Not)
True - water or other liquids will damage the objective lenses.
To measure the field diameter what procedures should be taken
Use your low-power measured field diameter to calculate the field diameter for high power. Position the slide so that a vertical line on the paper lines up with the edge of the field. Count the number of millimeters across the field to measure the field diameter.
In focusing on a specimen under the microscope, you must
When you are ready to change magnification, do not move the adjustment knobs before changing the objective lens. Once the image is clear, use the fine adjustment knob to focus on small details. If two images are visible, slowly move the body tubes closer together until you see with both eyes open, a single circular field of view.
Working distance
amount of space between the upper surface of the glass slide and the lowest part of the objective lens.
The _________ is the supportive frame of the microscope that joins the body tube to the base.
arm
Resolution is defined as
being able to see adjacent objects as separate.
The _______ is a small lens under the stage that narrows the beam of light and directs it through the specimen on the slide.
condenser
As magnification increases the diameter of the image being viewed
decreases
As magnification increases the field diameter
decreases
The focal plane thickness _________ as magnification __________.
decreases; increases
Working distance
distance between objective lens and the upper surface of the slide, with the specimen in focus
field diameter
distance from either side of the image through the center, which is dependent on magnification. As magnification increases the field diameter decreases.
The in-focus thickness of a specimen viewed under a microscope is called the _____________.
focal plane
All of the following are steps in setting up the microscope in order to view a specimen EXCEPT _________.
focusing
Depth of field is ______________.
greatest at low power and decreases as magnification increases
The virtual image being viewed through the ocular lenses is
inverted and opposite of the real image being emitted into the objective lens
Field of view
is the entire area that is seen when looking through the ocular lenses.
If the image through a microscope appears to be moving to the left
it is actually moving right.
At lower magnification the field diameter is
larger
Parfocal
lens design that allows specimens to remain near focused at different magnification powers
Compound microscope
microscope that uses more than one lens to direct light through a specimen mounted on a glass slide
Total magnification is determined by
multiplying the magnification of the ocular lens by that of the objective lens.
What part of the microscope is mounted on the nosepiece?
objective lenses
The _________ is the eyepiece where you place your eyes to observe the specimen.
ocular lens
Parfocal
refers to the ability of the microscope to stay nearly in focus when moving between objective lenses of different magnification.
The ability to distinguish between two objects located close to each other is called ____________.
resolution
Four basic steps in successfully viewing a specimen under the microscope?
setup focusing magnification
Depth of field
the amount (thickness) of a specimen that is in focus
As magnification increases ____________.
the field diameter decreases
Field of view
visible area that is seen when looking through the oculars.
