An overview of what you need to know about Microscropes

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The number of times greater and image is than the object


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The ability of a microscope to show two or more objects as seperate;

The closest together two points can be and still be distinguished


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Overall magnification

The product of objective magnification and the eyepiece magnification gives the overall magnification

Eyepiece magnification           Objective Magnification               Overall magnification

x10                                                                x4                                                    x40

x10                                                                x10                                                 x100

x10                                                                x40                                                 x400

x10                                                                x100                                               x1000

Eyepiece magnification x Objective Magnification = Overall magnification

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The microscopes

Light Microscope:

This uses the wavelength of light to magnify an image

Transmission Electron Microscope:

Electron gun produces a beam of electrons,parts of the specimen absorb electrons. These appear darker, whilst other parts of the specimen allow electrons to pass through and it appears brighter

Scanning Electron microscope: 

Electron gun produces a beam of electrons,
This is directed to the surface of the specimen rather than penetrating it from below.
Electrons are scattered by the specimen and the pattern of this scattering depends on the contours of the specimen surface 

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Light microscope

These are the features of Light microscopes

Energy source: Light

Lens: Glass

Best magnification: x1500

Best resolution: 200micrometres

State of speciment: 2D

Advantages: speciments are living and can be viewed in full colour

Limitations: Cannot reach level of magnification at a high resolution as Electron microscopes 

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Transmission Electron Microscope (TEM)

These are the features of a TEM
Energy source: Electrons

Lens: Magnet

Best magnification: x500,000

Best resolution:  0.1nm

State of specimen: 2D

Advantages:  There is a high resolution for this type of microscope

Limitations:   The specimens will be dead since they will be placed in a vacuum


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Scanning electron microscope (SEM)

These are the features of a SEM 

Energy source: Electrons
Lens: Magnet
Best magnification: x100,000
Best resolution: 0.1nm
State of speciment: 3D
Advantages: The image produced can be coloured by false-colour scanning. The image can also be in 3 dimensions, rather than 2D
Limitations: Specimens are dead, since they are placed in vacuum


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Key notes

  • Shorter wavelengths of light produce the best resolution
  • Magnets are used to focus electron beam rather than glass lenses: 

This is because glass absorbs electrons from the beam, where as the magnets attract the particles

  • A vacuum is used in electron microscopy

This is because electrons beams may be deflected by the molecules in air, if not used in a vacuum

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