A student calibrated an eyepiece graticule using a stage micrometer.
Each division of the stage micrometer was 0.01 mm.
With a 10 magnification objective lens, 10 eyepiece graticule units matched
10 divisions on the stage micrometer.
The same microscope was used with a 40, instead of a 10, magnification objective lens to
measure the diameter of an alveolus. The diameter of the alveolus was found to be 96 eyepiece
graticule units.
The eyepiece lens was not changed.
What is the best estimate for the diameter of the alveolus?
Calibration at ×10 objective
1 stage micrometer division = 0.01 mm
10 stage divisions = 0.1 mm
These match 10 eyepiece units
👉 So at ×10:
1 eyepiece unit = 0.01 mm
Switch to ×40 objective
Magnification increases 4×
So each eyepiece unit now represents 4× less real length
👉 New value:
0.01
mm
÷
4
=
0.0025
mm
0.01 mm÷4=0.0025 mm
Measure the alveolus
Diameter = 96 eyepiece units
96
×
0.0025
=
0.24
mm
96×0.0025=0.24 mm
Convert to micrometres: 0.24mm=240𝜇m
0.24 mm=240μm
