War, the magnification obtainable with a microscope was limited by the wavelength of visible light. This is because two points on a microscope specimen cannot be distinguished from each other if they are not at least as far apart as half the wavelength of the light used to illuminate them.

By using a beam of electrons instead of light as the illuminant, virtually any wavelength can be used by controlling the velocity of the electrons electrically. Thus, by subjecting a beam of electrons to a potential of 10 000 volts, a wavelength of about 10-9 centimetres is obtained, compared to visible wavelength of the order of 5 x 10-5 centimetres.

Glass lenses cannot be used with electron microscopes, instead a system of magnetic lenses is used for focusing the beam, and the resulting image is photographed on a special type of photographic plate. With the tremendous magnifications possible with this instrument, objects as small as individual viruses can be clearly photographed and observed.


Teacher: Your time is up. Now let’s do some exercises. The first is to find English equivalents for the following words and expressions in the text. Correct your translation, if you have mistakes

Microscope - a device that is intended to increase the image, as well as measurements of objects or parts of the structure that are invisible to the naked eye. Is a set of lenses. The set of production technologies and the practical use of microscopes called microscopy.

First microscope invented by mankind, were optical, and their first inventor is not easy to distinguish and name. The earliest information about microscope referred to 1590 and the city of Middelburg, in the Netherlands, and is associated with the name John Lippersgeya (who also developed the first simple telescope) and Hans Jansen, who were engaged in the production of glasses. A little later, in 1624, the year of Galileo is a compound microscope, which he originally called "okkiolino» (occhiolino Italian. - Small eyes). A year later, his friend from the Academy, Giovanni Faber proposed for a new invention, the term "microscope".

Microscope resolution - the ability to give a clear separation of the microscope image of two closely spaced points on the object. The degree of penetration into the microcosm, the possibility of its study depends on the resolution of the instrument. This characteristic is determined primarily by the wavelength of the radiation used in microscopy (visible, ultraviolet, X-rays). Fundamental limitation is the inability to get through electromagnetic radiation image of the object, smaller than the wavelength of the radiation. "To penetrate deeper" into the microcosm possible in the application of radiation with shorter wavelengths.

Depending on the required amount of permits considered particulate matter, microscopy, microscopes are divided into:

 

1. Optical microscopes.

 
2. Electron microscopes.


3. Scanning probe microscope.


4. X-ray microscopes.


5. Differential interference contrast-Mikros