Microscopy - Calculations

This lesson covers:

  1. How to use the equation "magnification = image size ÷ object size"

The equation you need to know for this subtopic is:

Equation showing magnification equals image size divided by object size

Magnification - how many times larger the image is, than the object

Image size - how large the object appears when you view it through the microscope

Object size - the real size of the object

Illustration showing an image 1000 times larger than the object with magnification of 1000x.

For example, here the image is 1000x larger than the object. 

How would you rearrange the magnification equation to find image size?

Image size = magnification ÷ object size

Image size = object size x magnification 

Image size = object size ÷ magnification 

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Diagram showing the calculation of magnification using a plant cell with a real width of 0.02 mm and a photograph width of 40 mm.

A plant cell in a photograph measures 40 mm in width. If the real width of the plant cell is actually 0.02 mm, what is the magnification? 

2000

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The nucleus in a photograph of a cell measures 1.5 mm across. If the magnification in the photograph is × 500, what is the actual size of the nucleus?

(Give your answer in mm)

0.003

mm

mm

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Illustration of a woodlouse viewed under a microscope.

Elouise finds a woodlouse that is 8 mm long. When she views it under the microscope it appears 12 cm long. 


What is the magnification?

15

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Illustration of a sperm cell measuring 5 micrometres in length.

A sperm cell is 5 μm long. How long will it appear when viewed under a microscope with a magnifying power of x1500? 

(Give your answer in mm)

7.5

mm

mm

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A scientist observed a skin cell using an electron microscope.

The size of the image was 25 mm, and the magnification was × 100,000.


Calculate the real size of the cell, giving your answer in nm. 

250

nm

nm

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Illustration showing a human egg cell with a width of 100 micrometres, a microscope with x 60 magnification, and a question mark asking for the size in centimetres.

A human egg cell is roughly 100 μm wide.

How large would it appear when viewed under a microscope at x 60 magnification? 

(Give your answer in cm)

0.6

cm

cm

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