Resolution of Microscopes ```Name: Paul T. Status: student Age: 16 Location: N/A Country: N/A Date: 1999-2001 ``` Question: I was wondering why the electron microscope has a much higher magnification(500'000X) compared to a light microscope(1500X). The LM uses lenses to increase magnification but the electron microscope does not have lenses. My lecturer told me that it has something to do with resolving power. She said that since the resolving power of an EM is 0.5nm while the resolving power of a LM is 0.2um, the EM will perceive 2 pts as further apart and so the whole image will be enlarged. As I said, I thought magn was achieved with lenses? I have learnt that the resolving power of a microscope is defined as the minimum distance by which 2 points must be separated in order for them to be perceived as 2 separate points rather than a fused image. From my understanding, the resolving power is the sharpness of a TV. but no matter how sharp a 21-inch TV is, 2 points on it, say, about 1 mm apart may not be perceived as separate, while the same points on a projection TV with the same sharpness may be seen as separate. Can anybody pls explain/clarify? Thanks. Sorry for the lengthy question. Replies: Paul - The short and simple answer to your long question is that the wavelength of light is greater than the wavelength of an electron. The shorter wavelength allows you to resolve points that are closer together. Larry Krengel Paul, Besides the influence of lenses -- be they glass in an optical microscope or magnetic like those in an electron microscope -- the resolving power of a microscope is a function of the wavelength of the "light" used to illuminate the specimen being examined. The shorter the wavelength, the better the resolving power. The wavelength of blue light is shorter than red. Thus, resolving power is improved on any optical microscope if the light is more blue than red. The wavelength of electrons are much shorter than that of light of any color. For that reason and a few others, the electron microscope holds the advantage over an ordinary light microscope. However, not all specimens can be examined under an electron microscope. The why of this is the subject of another discussion. Regards, ProfHoff I have learnt that the resolving power of a microscope is defined as the minimum distance by which 2 points must be separated in order for them to be perceived as 2 separate points rather than a fused image. From my understanding, the resolving power is the sharpness of a TV. but nomatter how sharp a 21-inch TV is, 2 points on it, say, about 1 mm apart may not be perceived as separate, while the same points on a projection TV with the same sharpness may be seen as separate. Can anybody pls explain/clarify? Thanks. Sorry for the lengthy question. Vince Calder The resolution limit depends on the wavelength and the quality of lenses. With perfect lenses, the achievable resolution is roughly equal to the wavelength. Visible light has a wavelength of around .5 micron; the electrons used in an electron microscope have such a small wavelength that it is not the limiting factor. Tim Mooney Click here to return to the General Topics Archives

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