Microscopes have developed over time. Early microscopes were light microscopes, which use light and lenses to magnify a specimen. Later, electron microscopes were developed. They use beams of electrons instead of light. An electron microscope has much higher magnification and resolving power than a light microscope. Resolving power is the ability to show two close points as separate, so a higher resolving power means a clearer, finer image.
This means that cells can be studied in much finer detail. With an electron microscope, biologists can see and understand many more sub-cellular structures, such as ribosomes and the inside of mitochondria, which a light microscope cannot show clearly.
Magnification = size of image ÷ size of real object. Rearranged, image size = magnification × real size, and to find real size you divide the image size by the magnification. Use the same units throughout. 1 mm = 1000 µm.
Example: a cell has a real size of 0.05 mm and its image is 20 mm long. Magnification = 20 ÷ 0.05 = 400, written ×400. Also, 0.05 mm = 50 µm, and in standard form 0.05 mm = 5 × 10-2 mm.