3 Microscopes

Microscopy

• Glass that is convex acts as a magnifying glass
• Compounded, convex glass is far more effective
• Light microscopes have a resolution of 0.2 micrometres
• Electron microscopes have a resolution of 0.1 nanometres

Resolution

• The minimum distance apart that two objects can be whilst still sistinguishable as different objects
• Depends of wavelength of the radiation
• Greater resolutions means greater clarity

Size of image = magnification x Size of real object

• First made in the 1930s
• Very short wavelength
• Focused using electromagnets
• 200 times greater resolution than the light microscope
• Needs a vacuum to stop the deflection of electrons

TEM

• Electron gun produces a beam of electrons through a specimen
• Specimen has to be thin for the electrons to pass through
• Resolution of 0.1nm
• Thinner parts allow electrons through and appear lighter on the screen

SEM

• Electrons are fired from above
• Electrons are reflected and scattered
• This scattering depends on the surface of the specimen
• 3D image is produced
• Lower resolution of 20nm

• High energy electron beam may destroy the specimen
• Vacuum doesn't allow lioving specimens
• Staining process is complicated
• Not in colour
• Slow
• TEM is 2D