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MIP 300 Lecture Notes - Bright-Field Microscopy, Tuberculosis, Flagellum

Microbio, Immun, Pathology
Course Code
MIP 300
Erica Suchman

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25 January
Properties of light
When rays of light pass from one medium to another (i.e. air to H2O) the rays bend –
Refractive index – measure of how greatly a substance slows the velocity of light
Amount and direction of bending are determined by the refractive indices of the
interfacing substances
4 Types of Light Microscope
Magnification = (objective) (eyepiece)
(40x objective) (10x eyepiece) = 400x magnification
Ability of lens to distinguish between objects is resolution or resolving power
Best light microscope resolution = 0.2 μm
Bacteria = 1 μm diameter. Only used to see shape, size and arrangement
Viruses = ~0.01 – 0.1 μm, too small to see with light microscope
Bright-field microscopy
Must stain bacteria
Background appears light, bacteria are color of stain
Dark-field microscopy
Light is refracted by organism, enters objective
Background appears dark, organism appears bright
Good for looking at things that are still alive
Phase contrast microscopy
Phase contrast converts slight differences in refractive indices into easily
detected variations in light intensity
Internal structures
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