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Microscopy
| Front | Back |
|---|---|
| Light/optical microscopy | - Visible light to make an image - light is refracted using optical lenses - magnification of 1000-2000 (best resolution 200nm) - low cost, easy preparation - living specimens can be analysed (non-destructive) |
| Light microscope | Magnification happens at the ocular and objective lenses - viewing magnification is calculated by multiplication of the ocular and objective powers |
| Ocular lens/eye piece | Person looks through to view sample Has its own magnification |
| Objective lens | Range of magnification lenses are available |
| Condenser | Focuses the light from the light source onto the sample and projects it to the objective lens |
| Iris | Controls the size of the cone of light which interacts with the sample |
| Measuring objects | Microscropes contain a graticule (eyepiece micrometer) Set of lines/divisions Stage micrometer is required to determine the size of the lines/divisions |
| Calibrating the microscope | Line up the 0 on the eyepiece micrometer and 0 on the stage micrometer Look over the lines until they line up |
| Calibrating | (Number of stage micrometer divisions / Number of eye piece micrometer divisions) x um per single stage micrometer divisions (10um) |
| Measuring objects after calibration | Line sample with some of the divisions Count how many divisions it spans across To work out the length of sample = number of division x the singular length between divisions |
| Bright field illumination | Light passes through a lens beneath the stage, this passes through the specimen, allowing observation of stains or natural pigments |
| Oblique lighting | used to cast shadows giving 3D appearance often used for impressions indicating ridges and furrows |
| dark field illumination | used for transparent specimen to show reflected and diffracted light against a dark background |
| calculating refractive index | n = c/v c = speed of light v = velocity of light in that material |
| Snell's law | n1 x sin (q1) = n2 x sin (q2) n = refractive indices of material 1 and 2 q = angles of light travelling through these materials when n1 > n2 = angle of refraction is smaller than angle of incidence |
| Comparative microscopes | 2 microscopes connected by an optical bridge used to analyse side by side specimens |
| polarised light microscope | can be used as regular light microscope polarised light filted can be used to view fibres |
| electron microscopy | scanning electron microscope (SEM) and transmission electron microscope (TEM) magnification up to 2 million times excellent resolution (2nm SEM, 1nm TEM) expensive and complicated cannot be living specimen |
Created by:
Mihaela07