What do electron microscopes use to view the specimen?
They use a beam of electrons with a wavelength of 0.004nm.
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Electron microscopes do not use lenses, what do they use instead and how?
They use magnets instead of lenses to focus the beam of electrons onto the specimen. The image produced from the beam is then projected onto a screen to make a black and white image (electron micrograph).
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Describe a transmission electron microscope
Electron beam passes through a thin prepared sample. Produces a 2D image. Magnification of up to x500,000
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Describe a scanning electron microscope
Electron beam is directed onto sample but is not passed through, instead it bounces off. 3D image produced. Magnification possible = x100,000
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What are the advantages of electron microscopes?
Resolution possible = 0.2nm which is better than a light microscope. SEM produces a 3D image which allows more detail of organelles and tissue arrangements to be see than in a light microscope.
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What are the disadvantages of electron microscopes?
The samples have to be placed in a vacuum as electron beams are deflected by air molecules. Electron microscopes are extremely expensive and preparing samples and using electron microscopes requires a high degree of skill and training.
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How can colour be added to the images?
Colour is added using specialised computer software and is known as false colour.
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Other cards in this set
Card 2
Front
Electron microscopes do not use lenses, what do they use instead and how?
Back
They use magnets instead of lenses to focus the beam of electrons onto the specimen. The image produced from the beam is then projected onto a screen to make a black and white image (electron micrograph).
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