if your eyepiece has a magnification of 10x and you are viewing through an objective lense of 20x, you multiply the magnifications, equalling a total magnification of 200x.
The compound microscope uses two lenses at once: the eye-piece lens and one of the objective lenses. The magnification of the microscope is the product of the magnifying power of these two lenses. This sounds complicated but it is very easy to calculate because the magnification is written on each of the lenses.
To calculate the total magnification of your microscope's lenses, multiply the ocular lens magnification by the objective lens magnification using the formula TM = (Ocular Lens) x (Objective Lens). For example, a 40x objective lens with a 10x ocular lens gives a total magnification of 400x. This process allows you to see how much larger the specimen will appear under the microscope.
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