Analysis

Determining Size and Uncertainty
From a Microscope Drawing

Introduction:
When you draw a cell or other object under a microscope, you must be able to determine the actual size of the cell and estimate the uncertainty in the size, based on your drawing. Here is an example of how to do that. The figure below shows a student's drawing of a cell in an onion root tip.

Finding the Size of the Cell                    Determining Uncertainty in Size of the Cell Uncertainty in FOV Measurement is ± 1 mm There were 2 measured values in this calculation measured diameter of the FOV on the drawing = 70 mm measured size of the cell drawing = 11 mm. Total Percent Uncertainty 1 mm/70 mm = 0.014 = 1.4% + 1 mm/11 mm = 0.091 = 9.1% =  (the percentages are added) 10.5 % Uncertainty Absolute uncertainty for cell size 31.43 microns x 0.105 (10.5%) = 3.30 mm ~ 3 mm Cell size reported correctly as 31 ± 3 microns

 

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