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14 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What are the two forms of electron microscopes?
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Scanning and Transmission.
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Often shortened to SEM and TEM.
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Explain their differences.
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Transmission passes electrons through a specimen and scanning hits the surface of the specimen with electrons, the reflected electrons can make an image of the surface of the specimen.
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How are magnets used in electron microscopy?
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Electrons are negatively charged so electromagnets can be used to alter the electron beam's path to focus the image.
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To do with the path of the electrons.
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Why must specimens be dead, kept in a vacuum and dehydrated?
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The specimen and fluorescent interceptor screen must be in a vacuum as air particles scatter electrons. In a vacuum water boils at room temp.
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What form of electron microscope would heavy metal staining be used and why?
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Scanning. Heavy metal stains are used to prevent electrons passing through the specimen. Another reason for the specimen having to be dead.
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Heavy metal staining would stop electrons passing through a specimen.
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What is a disadvantage of scanning electron microscopy?
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Lower maximum resolution than transmission.
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Why are electrons used?
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Because electrons have a much shorter wavelength, this wavelength is shorter when the electrons have greater energy. Because they are negatively charged they can easily be focussed using electromagnets, alternatives like x-ray microscopy does not allow this.
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The main limitation of light microscopy is the length of light waves.
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What is resolution?
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The ability to distinguish between two points.
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What is magnification and how is it worked out?
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The number of times larger and image is compared with the real size of the object. The formula to work out magnification is: Magnification = size of image ÷ actual size.
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How is the resolution affected by the wavelength of light (light microscopy)?
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The maximum resolution is half the wavelength of the radiation being used to view the specimen. For example with a light microscope if the wavelength of the light is 400nm the maximum resolution would be 200nm.
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How does colour affect the wavelength of light we see in light microscopy?
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Colours are just representing the length of the waves of light that the brain receives. So therefore different colours have different wavelengths, this allows us to see a higher resolution image under a light microscope when using different colours. Violet has the shortest wavelength (400nm) and red has the longest (700nm).
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How does the maximum resolution affect the image we see?
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If the maximum resolution is 200nm and two points on the specimen are closer than 200nm they will only appear as one... they cannot be separately distinguished. The wave of light is not interfered with by objects smaller than the wavelength as the wave passes over them.
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Can't we see more by magnifying the image more?
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No. Magnification only makes the image larger, it does not increase the quality or resolution.
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Why would a specimen need to be stained with a light microscope?
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If the object is transparent the light waves will just pass through which means it would not be visible. Staining it overcomes this problem.
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