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 inμ ( ) m LP = diameter in mm X1000 μm

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 inμ ( ) 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

€

width = 16 1200 X μ m = 200 μm

€

length = 12 1200 X μ m = 600 μm

Step 5

• Width

• Length

Practice

Problems

€

width = 14 1200 X μ m = 300 μm

€

width = 12 1200 X μ m = 600 μm

Practice Problem #1

• Width of Red Fiber

• Width of White Fiber

Couch Fibers

100X

€

height = 23 1200 X μ m = 800 μm

Practice Problem #2

• Height

Water Flea

100X

Practice Problem #3

Paramecia

100X

• Width

• Length

€

length = 13 1200 X μ m = 400 μm

€

width = 112

1200 X μ m = 100 μm