USE AND CARE OF THE COMPOUND MICROSCOPE

























































  

USE AND CARE OF THE COMPOUND MICROSCOPE

 

AIM: To study the parts, uses and care of compound microscope.

 

PARTS OF COMPOUND MICROSCOPE: A. Mechanical parts : B. Optical parts A. Mechanical parts : include a foot or base, an arm, a body tube, a stage and substage. The base is a rectangular box made up of heavy metal to give the maximum stability to microscope. The base consist of electrically operated self illumination in side. There is an on and off switch and an adjustable knob which is used to adjust the intensity of light also available. The arm is attached to the base.

      The arm carries the body tube in its upper part, and the stage and sub- stage in its lower part. The body tube is attached to the arm and can be moved up and down by means of coarse and fine adjustment screws. The body tube carries the eye piece in it upper part and the revolving nose piece in its lower part. The nose piece carries the three objectives. The coarse and fine adjustment screws are used to bring the object into focus. The stage is a rigid platform provided with a slide holder to keep the slide in position.

        There are two screws for moving the slide forwards, backwards and side ways. The stage has an aperture at its centre. Light passes through the aperture and through the slide into the objective lens of the microscope. The substage below the stage carries the condenser and iris diaphragm. B. Optical Parts include magnifying parts and illuminating parts. Magnifying parts are the eye piece and objective lenses. The eye piece fits into the top of the body tube. Usually two magnifications are available for the eye piece 5x and 10x. 5x is used when lower magnification is required and 10x, when higher magnification is needed. The purpose of the eye piece lens is to magnify the image formed by the objective lens.

         The objective lenses are attached to the lower end of the revolving nose piece. There are three objective lenses. 1. The low power objective lens of magnification 10 (10x). Working distance (focal length) is 16mm, the field under view is large. 2. The high power objective has a magnification of 40, (40x) or 45, (45x). The working distance (focal length) is 4mm. This is used for more detailed examination of a particular area. 3. The oil immersion objective has a magnification of 100 (100x). The working distance (focal length) is 1.6mm. Here a thin layer of air exists between the slide and the objective lens. As light passes through this thin layer of air (rarer medium) from glass (a denser medium), refraction of light rays will occur and very little light enters the objective, resulting in a blurred image.

          To prevent this, an oil having the same refractive index as that of glass is used to replace the air between the slide and objective lens. Oils such as Cedar wood oil, Canada Balsm and DPX are used for this purpose. The revolving nose piece allows any objective to be locked into position, being indicated by a ‘ click ’ . Usually in a microscope, if one objective is in focus, the other objective will be more or less in focus, when switched into position and requires only fine adjustment. This arrangement of objective is called parafocal arrangement.

 

 

 

 

 

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