Module 2: Microscopy Calculations
These free OCR A Level Biology Microscopy Calculations revision notes have been written for specification point 2.1.1(e).
When using a microscope to look at samples, it is useful to know the:
- Total magnification: The overall magnifying power of a microscope.
- Magnification: The factor by which the image of an object is increased compared to its actual size.
- Actual size: The true size of the object being observed.
- Image size: The measured size of the magnified object in the image.
Total Magnification (of a Microscope)
If you know the magnification of the eyepiece lens and the objective lens on your (optical) microscope, then you can calculate its total magnification.
Formula:
Total Magnification = Eyepiece Magnification × Objective Magnification
Where:
- Eyepiece Magnification: The magnification of the ocular lens.
- Objective Magnification: The magnification of the objective lens.
Magnification (of an Image)
If you have an image produced by a microscope and know the actual size of the object, then you can calculate the magnification.
Formula:
Magnification = Image Size ÷ Actual Size
Where:
- Image Size: The measured size of the image.
- Actual Size: The real size of the object.
A common mistake, or misunderstanding, is to measure the whole picture, rather than just the object of interest within it.
Actual Size
If you know how many times an image has been magnified and can measure the image of the object, then you can calculate what its actual size is.
Formula:
Actual Size = Image Size ÷ Magnification
Where:
- Image Size: The measured size of the image.
- Magnification: The magnification factor used.
Image Size
If you lack the actual image produced by a microscope, but know the magnification and the actual size of the object of interest, then you can calculate how big it appears in the image.
Formula:
Image Size = Actual Size × Magnification
Where:
- Actual Size: The real size of the object.
- Magnification: The magnification factor used.