Question

example #2: ocular power = 10x power objective = 10x high power objective = 40x the diagram shows the edge of a millimeter ruler viewed under the microscope with the lenses listed above. the field shown is the low - power field of view. a) what is the approximate width of the field of view in micrometers? b) what would be the width of the field of view under high power? c) if 5 cells fit across the high - power field of view, what is the approximate size of

Explanation:

Step1: Recall the relationship between magnification and field - of - view

The field of view is inversely proportional to the magnification. The magnification formula is $M = M_{ocular}\times M_{objective}$. The low - power magnification $M_{low}=10\times10 = 100x$ and the high - power magnification $M_{high}=10\times40 = 400x$.

Step2: Measure the low - power field of view

Assume we measure from the diagram that the low - power field of view (using the millimeter ruler in the field) has a certain width. Let's say by measuring the part of the millimeter ruler visible in the low - power field of view, we find that if 1 mm is visible in the low - power field of view, and since 1 mm = 1000 micrometers.

Step3: Calculate the high - power field of view

Since the magnification ratio of high - power to low - power is $\frac{M_{high}}{M_{low}}=\frac{400}{100}=4$. The width of the field of view at high - power is $\frac{1}{4}$ of the width at low - power. If the low - power field of view width is $w_{low}$, then the high - power field of view width $w_{high}=\frac{w_{low}}{4}$.

Step4: Calculate cell size

If 5 cells fit across the high - power field of view, and we know the width of the high - power field of view $w_{high}$, then the size of each cell $s=\frac{w_{high}}{5}$.

Let's assume we measure the low - power field of view width as 1000 micrometers.

• a) The low - power field of view width is 1000 micrometers (assumed measurement from the diagram).
• b) The high - power field of view width is $\frac{1000}{4}=250$ micrometers.
• c) The size of each cell is $\frac{250}{5}=50$ micrometers.

Answer:

a) 1000 micrometers
b) 250 micrometers
c) 50 micrometers