[Music] hi and welcome back to fre science lessons. co.uk by the end of this video you should be able to describe the advantages of an electron microscope over a light microscope you should then be able to carry out calculations based on magnification now microscopes were first invented hundreds of years ago and they looked something like this modern microscopes are much more advanced I'm sure your a picture of a modern microscope here both of these microscopes use light to view the specimen now over the years light microscopes have been used a lot to study cells they've allowed us to make important discoveries about the structures inside cells for example the nucleus and that's because microscopes allow us to magnify in other words the image that they produce is much bigger than the actual object now there are a couple of problems with light microscopes and we can see them with this cell first light microscopes have a limited magnification so for example we could not easily view structures inside the nucleus with a light microscope and that's because the magnification is not powerful enough light microscopes have another big problem which is that they have limited resolution what this means is that the image is blurred even if we could increase the magnification we'd still get a blurred image and we'd not be able to see fine detail again that's because the resolution is limited now scientists realized that if they wanted to explore structures inside cells in detail then a light microscope is not that useful so they invented the electron microscope I'm showing you an electron microscope here now the key advantages of electron microscopes is that they have a much greater magnification and resolution than light microscopes and you could be asked that in your exam this shows an image of a nucleus taken with an electron microscope and because of the high resolution we can now see detail in the nucleus that we could never see with a light microscope now we can calculate the magnification of a microscope using this equation the magnification equals the size of the image divided by the size of the real object you will be given this equation in the exam but you won't be given the triangle so it's worth learning here's a typical question use a ruler to measure the image size of the nucleus in millimeters the diameter of the real nucleus is 0.01 mm calculate the magnification so using a ruler we can measure the image size like this in this case the size of the image is 45 mm we know that the actual diameter of the nucleus is 0.01 mm the magnification is the size of the image divided by the size of the real object so 45 mm ided 0.01 mm gives us a magnification of 4,000 500 times here's a question for you to try measure the length of the mitochondrian shown the length of the real mitochondrian is .3 mm calculate the magnification so pause the video now and try this yourself okay from the ruler we can see that the image size is 30 mm the size of the real object is 0.03 mm putting these into the equation gives us a magnification 10,000 times now if we know the image size and the magnification then we can calculate the size of the real object to do that we need to use the triangle that we saw earlier the size of the real object is the size of the image divided by the magnification here's a question for you measure the length of the cell shown the magnification is 2,000 times calculate the real size of this cell in millimeters pause the video now and try this yourself okay so the size of the real object is the size of the image divided by the magnification the size of the image is 87 mm and the magnification is 2,000 times putting these numbers into the equation tells us that the size of the real cell is 0.435 MM remember you'll find plenty of questions on microscopes and magnification in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe the advantages of an electron microscope over a light microscope you should then be able to carry out calculations based on magnification [Music]