Name_________________________________________________ Period ________ Date _______________
MicroMeasurement Lab
Background: As you now have discovered, a microscope, as the name implies, is used to observe very small
structures. Exactly how small are these objects? Since using a ruler is not possible, we can’t really measure
them directly. Is it possible to use the microscope to help us determine the dimensions of such a small object?
Let’s investigate…
Two metric units are useful when measuring small objects:
1 meter (m) = 1,000 millimeters (mm) and 1mm = 1,000 micrometers, or microns (m)
Purpose: to learn how to measure using a compound light microscope.
-to measure the diameter of the low-power field
-to calculate the diameter of the high power field
-to measure specimens on prepared slides
Procedure: The following procedure is utilized to perform this experience:
1. Obtain a clear plastic ruler.
2. Look through the ocular at 40X and focus on the edge of the ruler using the coarse adjustment.
Adjust the ruler so that the view in the low power field is similar to what you see in the figure below.
Be sure you are looking at the cm/mm side of the ruler!
Empty area of field
Ruler
mm marking on ruler
3. Adjust the slide so that the edge of one mark is at the left side of the field of view and the ruler is at
the “equator” of your field of view (the illustration above isn’t quite lined up correctly). You want
the measurement of the diameter of the circle!
4. Note that 1 millimeter is the distance from the middle of one mark to the middle of the next mark.
What is the diameter measurement of your 40X field of view? Estimate to the nearest tenth of a
millmeter:
5. Now using the skills you have learned previously, convert the measurement from millimeters to
microns (show your work):
6. We can’t use the same method to determine the diameter of the high power field of view. Why not?
Try it out, then write the reason below:
©Mr. Comet’s Living Environment Laboratory Manual, 2005-2006, South Lewis High School, Turin, New York 13473. Permission is granted for not-for-profit
educational use by certified teachers.
7. Luckily, we can use math to help us with this problem. We can set up a ratio, since there is a
relationship between the magnification and the diameter of both lenses. Because it is an inverse
relationship, we can assume that:
high-power field diameter
low-power field diameter
=
low-power magnification
high-power magnification
Use this relationship, and your incredible algebra skills, to calculate the diameter of your 400X field of
view. Show your work in the space below (remember to include units as necessary).
Answer: 400X diameter = _________________________
Prepared Slide Observations
Find a prepared microscope slide that has a measurement scale printed in the center.
a. Focus the prepared slide on low power, then at medium and high power. Sketch the view at high
power, and note in the box below the diameter of medium and high power according to this scale.
How does it compare to your calculated measurement above?
Observed dimensions from scale on slide:
100X:
400X:
Comparison to calculated dimension above:
For the items below, sketch and make observations of prepared microscope slides of three different
organisms/cell types. For each one, record your observations and sketch the specimen at the highest appropriate
magnification. Be sure to estimate the size of the specimen (either the entire organism, or an average cell,
depending on the specimen) using the information you learned on the previous page!
.
Specimen:________________________________
Observations:
Approx. dimensions:
Magnification:_________________________
Date:_________________________
Specimen:________________________________
Observations:
Approx. dimensions:
Magnification:_________________________
Date:_________________________
Specimen:________________________________
Observations:
Approx. dimensions:
Magnification:_________________________
Date:_________________________
Analysis Questions
1. Calculate the diameter of the high-power field of a microscope with an ocular marked 10X, a low power
objective marked 10X, a high power objective marked 40X, and a low-power field diameter of 1600
micrometers.
2. What approximate fraction of the low power field AREA would you see if you were to change to the
high-power objective, using the microscope in question 1? Show your calculations or explain your
reasoning.