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An in-depth exploration of the various parts of a microscope and their functions, as well as the concept of magnification. Students are encouraged to memorize the parts and their functions, and to understand how magnification is measured and calculated. The document also includes a conversion table for metric units and a formula for determining the size of an object on the microscope.
What you will learn
Typology: Lecture notes
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a. base The foot on which the microscope rests. b. arm This is curved support for the lenses and their holder. The microscope should be lifted or held by the arm. c. stage The platform on which material to be examined is placed d. stage clips These are used to prevent movement of the slide e. body tube The main tube holding the lenses. It is of a standard length to hold the ocular and objective lens correctly positioned. f. revolving nose piece
The disc shaped piece at the lower end of the body tube. It holds in readiness several objective lenses.
g. objective lens Three long, compound lenses projecting from the revolving node piece. Your microscope has a low, medium and high power lens. Note they are of different lengths. The magnification of each is indicated on the side. Which one is the longest? Note also the diameter of the glass lens in each objective. Which one gathers light from the greatest area? h. ocular lens (eye-piece)
The lens fitted into the top of the body tube. It may be lifted out and replaced by one of different magnification. Its magnifying power is marked on top. Its function is to magnify the image from the objective lens. i. mirror If reflected light is to be used as a source of light, a two-sided mirror is fastened below the stage to reflect light upwards through the diaphragm. One side is concave to concentrate more light rays on the object. j. iris diaphragm Its function is to control the amount of light entering the microscope k. coarse adjustment
Move the body tube up a down until approximate focus is reached. It is used only when the low or medium power objective lens is in place. l. fine adjustment
It is used for adjusting sharpness of the image viewed under medium or high power.
m. inclination joint
This is the joint between the pillar and the arm of the microscope. It is used to tilt the body tube and stage. It is usually best to keep the stage horizontal.
Place the letters of the parts of the microscope in front of the functions which apply
Label the following parts of the microscope:
IV. Determining the size on the microscope.
A microscope object’s actual size can be determined based on the strength of the lens through which the object is being viewed, and the amount of the field that the object occupies. This can be expressed in the following formula...
Actual length of specimen (μm) =
Fraction of field occupied by specimen x (^) Diameter of field (μm)
Note As the magnification of an object increases the diameter of the field will proportionately decrease. ie. As magnification doubles, diameter of field is halved. Therefore as magnification. increases the object will occupy a proportionately greater area of the field of view.
eg. Low Power 40x Med. Power 100x High Power 400x Depth of field 4 500 μm 1 800 μm 450 μm
Quite often, you will be asked to draw an object that you see under the microscope. Based on the length of your drawing compared to the object’s actual length, you can calculate the magnification of the drawing. This can be done with the following formula;
Magnification of Drawing length (D) drawing (M) = Actual length (A)
Example
Drawing length = 30 cm ( 30 000 μm) Actual length = 30 μm Mag. of drawing =??
Magnification = D = 30 000 μm = 1 000X A 30 μm
Note: By manipulating the formula, you can solve for any one of the three variables if the other two are known.