Making Measurements with a Light Microscope

Metric Conversions

• • 1 mm = 1000 μm 1 μm = 1/1000 mm

Instructions

Step 1

• Place a transparent metric ruler under the low power (LP) objective (10X) of a microscope.

Step 2

• Focus the microscope on the scale of the ruler, and measure the diameter of the field of vision in millimeters (mm).

FOV (LP) = 1.2 mm



Step 3

• Convert this measurement to micrometers (μm) by using the following equation:

diameter in



m (LP) = diameter in mm X 1000



m mm

d (LP) = 1.2 X 1000 = 1200 μm

Step 4

 • Calculate the diameter in μm of the field of vision under high power (HP) using the following formula:

diameter in



m (HP) diameter (LP) x mag. of LP objective mag. of HP objective

d (HP) = (1200 X 10)/40 = 300 μm

Step 5

• To estimate the size of an object seen with a microscope under low power, first estimate what fraction of the diameter of the field of vision that the object occupies (LP). Then multiply the LP diameter you calculated in micrometers (step 3) by that fraction.

Size (μm) = fraction X 1200

Step 5

 • Width

width = 1 X 1200



m = 200



m 6

• Length

length = 1 X 1200



m = 600



m 2



Practice Problems



Practice Problem #1 Couch Fibers

• Width of Red Fiber

width = 1 X 1200



m = 300



m 4

• Width of White Fiber

width = 1 2 X 1200



m = 600



m



100X



Practice Problem #2 Water Flea

• Height

height = 2 3 X 1200



m = 800



m 100X



Practice Problem #3 Paramecia

• Width

1 width = 12 X 1200



m = 100



m

• Length

length = 1 X 1200



m = 400



m 3



100X