[Music] hi and welcome back to free science lessons by the end of this video you should be able to work with micrometers and nanometers you should then be able to describe the uses and limitations of the light microscope for studying biological specimens we're going to start by looking at micrometers and nanometers now this can seem a bit tricky so it's worth watching this section A few times until you get the idea you're probably used to working with millimeters remember that one meter is divided into one thousand millimeters A millimeter is about the length of this fingernail now in biology A millimeter is actually a very large size objects and biology are often much smaller than this if we divide one millimeter into one thousand equal parts then we have a micrometer a bacterium such as E coli which is found in the human large intestine is around one micrometer in length in biology a micrometer is still quite large objects inside cells can be smaller than this if we divide one micrometer into one thousand equal parts then we have a nanometer a typical ribosome from a human cell is around 25 nanometers in diameter now I should point out that you often have to convert numbers between different units so you need to learn that one millimeter equals one thousand micrometers to convert from millimeters to micrometers we multiply by one thousand one micrometer equals one thousand nanometers and to convert micrometers to nanometers we multiply by one thousand okay now we often use a light microscope in biology and I'm showing you a light microscope here the first light microscopes were invented in the 1600s and I'm showing you here a replica of an early light microscope both the early and modern light microscopes have several features in common they both have an eyepiece lens they both have a stage for the specimen and they both have a focusing dial now the first light microscopes could magnify around 300 times whereas a modern light microscope can magnify around 1000 times and we're going to be looking at magnification in a later video light microscopes have one big advantage over other types of microscopes and this is that we can use light microscopes on living cells this means that we can explore processes such as cell division or movement of cells however sometimes we need to use a stain and these can kill cells now there's one big problem with light microscopes which is the problem of resolution and this is due to the nature of light itself so what's meant by resolution resolution is the ability to distinguish between two separate objects let's look at an example this diagram shows a low resolution image you can see that the image is blurred and it's hard to make out detail here's a high resolution picture of the same image and we can see that the level of detail is not much greater look at the area shown by the arrow in the low resolution image we can see a blurred red object however in the high resolution image we can see that this is actually three separate objects so resolution is the ability to distinguish between two separate objects now we need a more scientific definition for a level biology in a level biology resolution is defined as the minimum distance between two objects where they can still be seen as two separate objects and that's a key definition which you need to learn for a standard like microscope the limit of resolution is around 200 nanometers as I said before this is due to the nature of light the wavelength of visible light is around 400 nanometers to 700 nanometers if two objects are closer than 200 nanometers then we cannot see them as two separate objects using a light microscope in this case we can use an electron microscope and we're going to look at that in a later video okay so hopefully now you can describe light microscopy [Music] thank you