Name: ___________________________________________________________ Hour: ________
Microscope Lab: Estimating Size and Calculating Magnification.
Part 1: Microscope Handling
1. Carry the microscope with both hands --- one on the arm and the other under the base
of the microscope.
2. One person from each group will now go over to the microscope storage area and
properly transport one microscope to your working area.
3. Remove the dust cover and store it properly. Plug in the scope. Do not turn it on until
told to do so.
4. Examine the microscope and locate each of the parts listed on your notes and
complete the drawing below.
Part 2: Estimating Size of Specimens under the Microscope
Purpose: To determine an approximate field diameter for each of the objective lenses on our
microscopes.
Background Information:
When viewing a small organism through the microscope, it’s usually necessary to have some
idea of its size. Therefore, you need to have some means of estimating the size. When someone
is standing near a doorway, you can estimate their height by comparing them to the doorway. In
the same way, you can estimate an organism’s length by comparing it to the field of view that
you are using.
Example: If the “doorway is 10 units, how high is the stick person?
Answer: Approximately
6 units high.
Procedure:
To calculate the diameter of the field of view for low and medium power.
1. Use the following 2 tables to record your information. You will each want to write both
these tables down on the back of your notes.
Table 1:
Magnification of
Field Diameter
Field
Calculated
Average
Microscope
(mm)
Diameter
Constant
Constant for
(FD x
Microscope
(m)
Magnification)
LOW
(______X)
Medium
(______X)
High
(_______X)
Table 2:
Magnification of
Microscope
LOW
(______X)
Medium
(______X)
High
(_______X)
Field Diameter (mm)
(Class Average)
Field Diameter (m)
(Class Average)
2. Calculate the total magnification of the low power objective lens by multiplying the
magnification of the ocular lens (eye piece) by the magnification of the objective lens.
The magnification of the lenses is etched on the sides of the actual lens holders. For the
objective lens on the nosepiece, they are written in decimal form. You will need to
multiply this number by 10. (ex: Low power says 0.10 that equals 10X)
3. Locate the numbers on the eyepiece and objectives and fill in the blanks below.
Low Power Objective
Eyepiece magnification
______________
(X)
Objective magnification
=
______________
Total Magnification
_____________X
(X)
Objective magnification
=
______________
Total Magnification
_____________X
(X)
Objective magnification
=
______________
Total Magnification
_____________X
Medium Power Objective
Eyepiece magnification
______________
High Power Objective
Eyepiece magnification
______________
3.
Write out the rule for determining total magnification of a compound microscope.
_____________________________________________________________________________
4. Record and transfer the Magnification of all power levels for your microscope from the
above section to table 1.
5. Take a clear plastic ruler and examine the millimeter scale under low power.
6. Place the center of one of the scale marks along the edge of the field as shown below.
7. Count the whole number of millimeter spaces. If there is part of a spacing, estimate (in
decimals) the size of the millimeter portion that shows. Record the field diameter in
millimetres in your data table 1.
Example:
The distance across this field of view is 4.2 mm.
8. Convert the field diameter for low power into micrometers and record this number in
your data table 1. (1000 m = 1 mm) (For the example above: 4.2 mm= 4200 m)
9. Repeat steps #3-6 for the medium power objective lens. Do not use the ruler with high
power.
Procedure to calculate the field diameter for high power lens.
The field diameter for high power cannot be measure directly using your ruler because this
field diameter is LESS than one millimeter. Therefore, we must calculate the field diameter a
different way.
All microscopes have a “constant” number that can be calculated:
Field diameter x total magnification = a constant
Once you know what the constant is for your microscope, you can use it to solve for the
field diameter.
Example: The constant for my microscope at home is 145. High power is 400X. What is the
field diameter for my microscope at high power?
Field diameter x total magnification
= a constant
Field diameter x 400X= 145
Field diameter = 145/400
Field diameter = 0.36 mm
(Field diameter = 360 m)
1. In your data table, calculate the constant for both low and medium power. If you use
the field diameter in millimeters for the first calculation, then you must use millimeters
for the second calculation. It does not matter if you use millimeters or micrometers, just
as long as you do the same for both calculations. The “constant” that you calculate will
probably not be the same since we have been ESTIMATING the field diameter, and there
is bound to be some error.
2. Take the average of the two constants calculated. Record this number in your data
table. From now on, it is the AVERAGE constant that you will use for your calculations.
(All three powers will have the same average constant)
3. Calculate the field diameter for the high power lens using the formula: field diameter x
total magnification = constant. Substitute the known values for the total magnification
and the constant (the average) and then solve the equation for field diameter.
4. Complete the data table 1.
5. Compare your data table 1 with the rest of the class. Record your field diameters on a
common chart that is with Mr. Parrott.
6. Calculate the class average field diameter for each power and record this information in
Data Table 2. We will use these values from now on when we are estimating the size of
specimens under the microscopes.
Part 3: Preparing a wet mount of the letter "e”.
1. One person from each group will pick up a pair of scissors, part of a newspaper, a slide,
a cover slip, and a small beaker of water.
2. With your scissors cut out the letter "e" from the newspaper.
3. Place it on the glass slide so as to look like (e).
4. Cover it with a clean cover slip. See the figure below.
4. Using your eyedropper, place a drop of water on the edge of the cover slip where it
touches the glass slide. The water should be sucked under the slide if done properly.
Technique for Adding a Stain or Water when making a Wet Mount
5. Turn on the microscope and place the slide on the stage; making sure the "e" is facing
the normal reading position (see the figure above). Using the course focus and low
power, move the body tube down until the "e" can be seen clearly. Draw what you see
in the space below. Off to the side record how long the letter e is in millimeters and
convert that into micrometers using the data from earlier. At the very bottom right
corner give the magnification of low power to identify that it was done at low power.
6. Describe what the letter “e” looks like through the eyepiece compared to what you see
on the stage (normal vision).
________________________________________________________________________
7. Looking through the eyepiece, move the slide to the upper right side the stage. What
direction does the image move?
_________________________________________________________________________
8.
Now, move it to the lower left side of the stage. What direction does the image move?
________________________________________________________________________
9. Re-center the slide and change the scope to medium power. You will notice the "e" is
out of focus. DO NOT touch the coarse focus knob (the big one); instead use the fine focus
(little one) to resolve the picture. Draw the image you see of the letter e (or part of it) on
medium power. Also, using the field diameters from earlier, measure the length (or some
other significant part) of the e in mm and m. Also, write the magnification of medium
power.
10. Locate the diaphragm under the stage. Move it and record the changes in light
intensity as you do so. Start at 5 and go to 1.
________________________________________________________________________
4. Remove the slide and clean it up. Returning the slide and cover slip back up front.
Clean up Rules
Turn off the microscope and wind up the wire so it resembles its original
position. Place the low power objective in place and lower the stage.
Cover the scope with the dust cover. Place the scope back in its original
space in the cabinet.
Part 4: Choose two different slides from the box in the front of the room. On the line, write
the name of the object you are drawing and then draw it underneath low power and medium
power. On the second line you will measure a certain section of your drawing in micrometers
(um). Circle the section that you measured in your drawing.
______________________________
______________________________
______________________________
______________________________
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Conclusion Questions:
1. State 2 procedures which should be used to properly handle a
light microscope.
2. Explain why the light microscope is also called the compound microscope.
3. Images observed under the light microscope are reversed and inverted. Explain what
this means.
4. Explain why the specimen must be centered in the field of view on low
power before going to high power.
5. A microscope has a 20 X ocular lens (eyepiece) and two objectives of 10 X and 43 X
respectively.
a. Calculate the low power magnification of this microscope. Show your formula
and all work.
b. Calculate the high power magnification of this microscope. Show your formula
and all work.
6. In three steps, using complete sentences, describe how to make a proper wet mount of
the letter “e.”
7. Describe the changes in the field of view and the amount of available light when going
from low to high power using the compound microscope.
8.
Explain what the microscope user may have to do to combat the problems incurred in
question # 7.
9.
How does the procedure for using the microscope differ under high power as opposed
to low power?
10. Indicate and describe a major way the stereomicroscope differs from
the compound light microscope in terms of its use.