Tools of ScienceThe 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 (400-700nm 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!!!

TEMTransmission 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.

Confocal Microscopy