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Calculations Related to the Microscope:

Source: www.saskschools.ca/curr_content/biology20/unit1/UNIT1MODULE2LESSON4.htm

1) Calculating the magnification of a microscope:

Total magnification = magnification of eyepiece x magnification of objective lensOcular Lens - W10XD (Look for a whole

number or a number followed by an X to

determine the power.

Low Power

Objective - DIN4

10X ocular x 4X

objective = 40X

total

Medium Power Objective - DIN10

10X ocular x 10X objective = 100X total

2) Measuring the microscope field of view on lowest power:

Place a clear plastic ruler with mm markings on top of the stage of your microscope. Looking through the lowest p

mage. Count how many divisions of the ruler fit across the diameter of the field of view. Multiply the number of d

field of view in micrometers (m). Record this in m (1mm = 1000 m ).

Magnified at 40X, the lines of the ruler

are clearly visible. However, in order to

accurately measure the field of view, one

ine should be moved to the edge of the

field of view, as shown in the image to

he right.

Now that one of the

lines has been moved to

the extreme left, it is

easier to determine the

field of view:

2 mm x 1000 = 2000m

(image @ 40X)

In this example, the field of view would be calculated:

3 mm x 1000 = 3000 m

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3) Calculating the microscope field of view on other powers:

. Using the above procedure, determine the field of view in micrometers (m) for the lowest power on your micros

i. After you have determined the field of view for low power, use the equation below to mathematically calculate th

powers:

Microscope Calculations Practice Questions

Using the formulas you have just learned, complete each of thefollowing questions.

1. A microscope has an eyepiece lens with a power of 5X. The objective lens

being used has a power of 10X.

Total magnification =

2. A microscope has an eyepiece lens with a power of 15X. The objective lensbeing used has a power of 40X

Total magnification =

3. A microscope has an eyepiece lens with a power of 10X. The objective lensbeing used has a power of 10X.

Total magnification =

4. Sue observes a clear plastic, millimeter ruler under low power of hermicroscope. She sees three divisions of the ruler. What would be the fielddiameter of Sues microscope on low power? (in micrometers ('m')

5. Convert each of the following to micrometers (m).

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a) 3.5mm

b) 4.0mm

c) 1.5 cm

d) 0.5 cm

6. The following information is for a microscope which has an eyepiecelens (ocular lens) with a power of 10X:

Objective Lens Power Field Diameter

low 4X 3500 m

medium 10X ?

high 40X ?

Using the information provided above, calculate the field diameter for mediumand high power.

Microscope Calculations (continued)

4) Estimating the size of an object:

You must first calculate the diameter of the field of view for the power of magnification you are using.

Looking through the eyepiece, estimate how many times the object will fit across the field of view. Calculate the size of the object using the formula below. Remember to use um

Example:

The image of the amoeba to the left is seen under medium power (10magnification).

If the diameter of the field of view on low power (40X) for this micro

4000 m, first calculate the diameter of the field of view for medium

follows:

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Second, estimate the number of times the object (amoeba) fits across the

view. Unless otherwise instructed, estimate using the longest dimension oIn the image to the left, the amoeba would fit across the field of view app

times. Because the diameter of the field of view for medium power was c

1600 m, the size of the object would be calculated as follows:

Therefore, the approximate length of the amoeba is 800 m or 0.8mm

The final calculation you will need to use when using the microscope is to calculate the magnification

drawing. (This is a way of calculating how many times larger your drawing is in relation to the estima

the object.)

5) Calculating the magnification of your drawing:

First calculate the size of the object using the procedure outlined above. Using a ruler, measure the size of your drawing and convert units to um. (In the diagram below a ruler

has been superimposed on the drawing to illustrate how to measure. The image in this particularexample is 13.7cm or 137mm, which converts to 137 000 m.)

Calculate the magnification of your drawing using the formula below the diagram.

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This number indicates how many times larger your

drawing is relative to the actual size of the object.

This number should appear at the bottom of yourdrawing.

Calculations Related to the Microscope

Anne viewed an amoeba under the high power 40X objective lens on her microscope.

She drew the following picture of that amoeba:

She needs to calculate the magnification of her drawing. Other important information

includes:

Eyepiece lens = 5X Low Power Objective = 4X Low Power Diameter of Field of View = 4.2 mm Estimate of the number of times object fits across field of view (high

power) = 4.5

*Anne used the longest dimension to estimate.

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a) Convert the diameter of field of view on low power to um.

b) Calculate the total magnification under low power and high power.

c) Calculate the diameter of the field of view under high power.

d) Calculate the size of the object under high power.

e) Measure the size of the drawing. Convert to um.

f) Calculate the magnification of Annes drawing.