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Biology 11-Microscope Calculations
1. Using a ruler, you found that the size of your field of view (fov) at low power (40x) was
4mm.
(a) Change 4mm to µm. Remember that 1mm = 1000 µm.
(b) Calculate the size of your fov at 100x. Remember that to find the new field
size you need to use this formula:
New field size = Original field size ( the one you measured at 40x)
The number of times the magnification has increased
(c) Calculate the size of your fov at 400x.
2. Calculating the Size of an Object Observed Through the Microscope
Object size = Size of fov in µm__
Number of times
Object fits across fov
(a) The amoeba above was observed at 100x. Calculate the size (length) of this amoeba
in µm, using the above formula.
(b) Use the object size formula to find the width of the amoeba in µm.
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3. Calculating Drawing Magnification (DM)
When you sketch an object that you are viewing under the microscope, you are making it
much larger than its’ actual size. The larger the sketch, the greater is the “magnification”
of the object. As the artist you can control how big you want your sketch to be. The
bigger the sketch the greater is the DM. To find out how much your sketch has magnified
the object use the following formula:
Drawing Magnification (DM) = The size that you made your drawing of the object
The actual size of the object
Example:
Calculate the DM for the Amoeba in the above sketch:
Step 1- Measure the size (length) of your sketch using a ruler. Your measurement will
be in mm and then changed to µm. In this example the amoeba is 130 mm in length.
130 mm x 1000 = 130 000 µm.
Step 2 – You are told that the actual size of this ameba is 800 µm.
Step 3- Use the above formula to find the DM of the ameba that you sketched:
DM = The size that you made your drawing of the object
The actual size of the object
DM = 130 000 µm = 162.5x
800 µm
Your DM is 162.5x. This means that because you made the sketch this size, it has
magnified the ameba 162.5 times its’ actual size!
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DM continued
Answer the following questions based on the sketch of the amoeba shown below:
(a) How do you think the DM in the example on page 2, will compare to the DM for
this sketch? Smaller or larger? Why?
(b) Calculate the DM on the basis of this sketch. Show your work.
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A very rare organism known as the triangicium was observed under the microscope at
low power (40 X). Assume the fov at 40 x is 4 mm.
(a) Estimate how many triangicia could fit across the fov.
(b) What is the actual size of a triangicium in µm? Show your work.
(c) Calculate the DM of the trangicium shown the sketch. Show your work.
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