Download Tools of Science - Bergen County Technical Schools

Tools of Science
The Microscope
The Microscope
An instrument that can form an enlarged
image of an object.
Visible light is passed through the
specimen and through glass lenses. The
lenses refract light to enlarge the image
projected to the eye.
Schematic of Light Microscope
Properties of Microscopes
Magnification- how much
larger compared to the
real size
The two lenses are the
ocular and objective lens.
To determine
magnification, multiply the
magnifying power of the
ocular by the magnifying
power of the objective
lens.
Properties of Microscopes
Resolving Power
a. a measure of clarity
b. minimum distance between two points that
can still be distinct as two points.
Limitation on Resolution
• Limit is .2 micrometers
• Limit is set by the wavelength of light (400700nm or .4 micrometers)
Rayleigh Criterion
The Electron Microscope
• 1931 Ernst Ruska invented the electron
microscope
• Beam of electrons focused by magnets.
• Wavelength of a resonating electron is .004nm.
The resolution is limited by the ability to focus
electrons with a magnet to approximately .2nm.
• The resolving power of the microscope is
inversely related to the wavelength of
electromagnetic radiation used.
• The specimen will be dead!!!
TEM
Transmission electron microscope
used to view internal structure.
200,000x
SEM-Scanning Electron
Microscope
Surface sprayed with
metallic mist.
Scans surface of
objects with electrons.
Electrons bounce off of
surface and are
projected on a
screen.
Image appears 3D.
100,000x magnification
of cell surface
ultrastructure.
Schematic of SEM
Scanning Tunneling Microscope
• Specimen can be
living!!!!
• 100 million x
• Electrons tunnel off of
any surface and and
electron gun measures
the electron cloud
thickness.
• Uses electrons that leak
from the surface.