Microscope Working and Principle. Resolving Power, Resolution, Numerical Aperture and Magnification of microscope.

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 MICROSCOPE


A microscope is an instrument that allow to observe objects and structures called as specimen that are too small to be seen with the naked eye. 

A microscope can be Optical or Electrical

A microscope magnifies the tiny objects by using lenses enabling to study microorganisms, cells, and fine details of materials.

Microscope uses the Light as the source to observe the specimen. It can be sunlight or an electrical source.

HISTORY of MICROSCOPE

  • The first use of the microscope to see microorganisms was by the Dutch merchant Antonie van Leeuwenhoek (1632 1723). With these microscopes, van Leeuwenhoek was the first to see “animalcules,” which today are known as microorganisms.
  • Microscopy is a highly subjective tool, provide extremely useful information about microorganisms.
  • Microscopy techniques rely on the manipulation of light (or electrons in electron microscopy) to influence the resolution of a specimen.

PRINCIPLE of MICROSCOPY

  • Microscopy is based on the principle of Collection and Focusing of Light using phenomena of Refraction, Magnification and Resolution.
  • Magnification: It means amplification of size of image or increasing the size of an image. The specimen on a slide can be magnified using objective lens and ocular lens (eyepiece), Condenser lens also helps in this. 
  • Resolution: It is the ability to distinguish between two closely spaced points of objects. 

Figure 1 is an Unresolved structure of two objects if seen without microscope, using microscope this can be seen as two objects as in Figure 2. Microscope helps to distinguish between two points of an object.


  • Resolution can be calculated in terms of Resolving power or Resolving limit. Designated by 'd '.
  • 'd 'can be defined as the minimum distance between two points that can be distinguished by a micrscope.
                                                               d=0.61λ /NA
  • This is the formula for Resolving power.
  • Where λ is the wavelength of light used in microscopy.
  • NA = Numerical Aperture, that is the ability of the lens to collect the incident light rays.
  • Resolving power depends on the wavelength of light used and the Numerical Aperture of the lens.

What is a Good Resolution?

  • For good resolution of a microscope the resolving power should be Low.
  • Low resolving power can be obtained using light of Lesser Wavelength and lenses having Higher Numerical Aperture



QUESTIONS

The resolving power of human eye is   (PGT Biology)

50 micrometer

150 micrometer

100 micrometer

200 micrometer

 Smallest size of cell seen by naked eye is

1 micrometer

100 micrometer

10 micrometer

100  micrometer


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