Transcript
The microscope
The microscope The microscope is an optic instrument used in bio Logical and medical research .Because most cells are too small to be seen by the naked eye ,the study of cells has depended heavily on the use of microscope . -In the light microscope , the light rays passage through a specimen are brought into focus by a set of glass lenses ,and the human eye then views the resulting image . the limit of resolution of the light microscope is a approximately 0.2Mm and magnified objects up to about 300 times their actual size .
Parts of the microscope A-The mechanical parts : -
Serve to connect all the parts of the microscope and support its relative position : 1- Foot (Base):- A horse - shoe shaped structure with the microscope . 2- Arm :-A curved solid structure with which the microscope can be handled . 3- Stage :- A horizontal platform upon ,which rests the object to be examined .There is a hole in center through which the light reflected by the mirror will be directed to the slide.
A-The mechanical parts :
4- Tube :- is a hollow part in front of the arm having an eye –piece on its top . 5-Nose- piece :- A revolving disc at the lower part of the tube provided with holes to fit the objectives. 6- Clips:- To structure used to fasten the slide to the stage.
7-Coarse adjustment :-A large knob at both sides of the arm used to move the tube up and down at a noticeable distance. This adjustment must be used with the low-power only. 8- Fine adjustment:- A smaller knob lie above the coarse adjustment, it is used for focusing with the high –power.
B- The optic parts :-
Two sets of lenses situated at the top and bottom of a tube. The upper set is known as the eye-piece, and the lower set as the objective . 1- Eye-piece(ocular): A metallic case with two lenses inserted into the upper part of the tube .the power of an ocular is indicated on it ,which is either 10x or 12x . 2-objective :- Each is a combination of lenses at the lower and of the tube ,they are fixed to the holes in the nose- piece at the certain distance from one another . -The microscope may carry more than tow objectives . the objective, which is under the tube , is said to be in position .the other is out of position.
A-The low – power objective (L.P.) :- Is the shorter one ,it has lesser magnification ,power e.g. 3.5 x ,5x and 10x . B- The high –power objective (H.P.):- Is the larger one ,it has larger magnification – power e.g. 40x, 100x, (oil immersion lens).
C- the illuminating parts:-An arrangement to illuminating the object. 1- Mirror :- A movable disc with tow faces, plane and concave used for reflecting the light . 2-diaphragm :- An arrangement which gradually opens and closes the hole in the stage and is worked by means of the lever placed below the stage , it is used to regulate the amount of light admitted through the condenser. 3-Condenser:- A series of lenses between the mirror and the stage , which reflects the light to the object . the condenser can be moved up and down by knob. 4-Filter ring :- Beneath the Diaphragm is a ring for carrying a filter .
How to use the microscope?
1-Hold the microscope from its arm horizontally. 2-Use the mirror whenever the electricity is available. 3-Turn the revolver disc to put the low- power lens in its position until you hear a faint dick. 4-Fit the slide on the stage and look through the eye –piece ,use the coarse adjustment to clear the image . 5- change to high – power objective , using the fine adjustment to clear the image. 6- change to oil lens , then put a drop of cedar oil on the slide when examining the minute organisms. Not: Don’t use the coarse adjustment with high power (40x or 100x) but use the fine adjustment only.
