LAB: MEASUREING WITH THE MICROSCOPE
Name ________________________
S-W-1899
Hour ______
INTRODUCTION: Biologists often wish to know the size of the objects they are examining under the microscope.
Metric units of length such as the millimeter and centimeter are too large to be used as these objects are usually very
small. The unit of length that is commonly used for measuring microscope objects is the MICRON, which is given the
symbol of the Greek letter  (called "mu").
REMEMBER:
1 micron =
1000 =
0.001 mm
1 millimeter
PURPOSE: To estimate the size of some microscopic objects.
PROCEDURE:
1.
2.
3.
4.
With the low power objective in position, place the millimeter ruler on the center of the stage of the
microscope so that you can clearly see the scale as you look through the eyepiece.
Carefully move the ruler until one of its vertical lines is lined up with the left boundary of the circular field
of vision in the microscope.
The lines on the ruler now appear quite wide. The distance from the center of one line to the center of the
next line is one millimeter. Count the number of millimeters covered from one side of the field to the
opposite side. If the right side of the field does not coincide exactly with one of the lines on the ruler,
estimate the fraction of the millimeter which is included in the field. Record this information in the chart
provided.
Carefully rotate the high power objective into position. Note that now the diameter of the field of view is
less than one millimeter. Instead of attempting to measure the diameter of the high power field directly,
more accurate results are obtained by using the following methods:
a. First divide the magnification of the high power objective by the magnification of the low power
objective.
EXAMPLE: high power = 40x
your high power _______________
low power = 10x
your low power ________________
40𝑥
10𝑥
=4
b. Now divide the diameter (in microns) of the low power field by this quotient (from part a above). The
quotient obtained from the division is the diameter of the high power field.
EXAMPLE:
If the low power field has a diameter of 1600 microns, then:
1600𝜇
4
5.
= 400𝜇 = diameter of high power
Complete the following chart:
Low Power Field
Diameter in mm
Diameter in 
Medium Power Field
High Power Field
6.
Now remove the plastic ruler from the stage and prepare a wet mount of a small section of newspaper
print - use a regular size print letter "e". Examine the letter "e" under low power. Compare the height of
the letter with the diameter of the field of view. If the height of the letter is one-fourth of the diameter of
the low power field, and if you estimated the diameter of this field to be 1600, then the height of the
letter "e" is 400.
a. Estimate the height of the letter "e" in millimeters. _________________
b. Estimate the height of the letter "e" in microns. ____________________
7. Find two other slides and determine the size of the cell in millimeters and microns on high and low power.
Specimen 1
Size in mm
Specimen 2
Size in m
Size in mm
Size in m
Low Power
High Power
GOING FURTHER
1.Calculate the area of your low power field and your high power field in square millimeters.
REMEMBER: The area of a circle can be calculated by using the following:
Area = r2
where  = 3.14 and r = one-half the diameter of the circle
Which field of view has the largest area? _________________________
2.The average human red blood cell has a diameter of about 7.5. How many red blood cells could be placed side by
side across the diameter of the low power field? The high power field? Show your work!
3. Approximately 500 of a certain type of bacteria can fit across your low-power field of vision. What is the
approximate size of 1 bacterium? Show your work!
4. Approximately 7 of a certain type of protist can fit across your high-power field of vision. What is the approximate
size of 1 protist? Show your work!
5. If 20 objects fit across a low-power field of view whose field diameter is 3000 micrometers, what is the
approximate size of each object? Show your work!