Question

1. Select a contrast mode in microscopy. In the space below, describe and illustrate it in detail (hint: phase, dark-field, bright-field) (1 page limit)

Answer 1

Light microscopy	Electron microscopy
Lenses are made of glasses.	No glass made lens, rather electromagnets are used.
Illuminating source is light.	Illuminating source is beam of electrons.
Section is placed on a slide.	Section is placed on a copper grid.
Principle of image formation is differential transmission of light.	Principle of image formation is differential transmission of electron beam.
Uses live or dead specimens	Only uses dead specimens.
Focusing done by adjusting course adjustment	Focusing done by manipulating the current
No requirement of vacuum.	vacuum is required and whole column has to be evacuated, otherwise electron beam will lose energy.
Image captured directly on screen.	image obtained on a fluorescent screen coated with zinc sulphide.
Chromatic dyes (coloured compounds) are used.	Electron stains (dark coloured compounds) used.
Resolving power is 0.3 micrimetres	Resolving power is 0.03 angstron.
Range of section length is 5-10µm	Range of section length is 10-15nm.

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