CARE & USE OF THE MICROSCOPE

The human eye is unable to perceive objects less than 0.1 mm in diameter.A microscope becomes an essential tool for the study of small objects, such as the cell.The microscope utilizes an eyepiece system that magnifies objects.Magnification can range from approx. 10 - 2000 times (x) the diameter of the specimen being observed.

Objectives of Lab - to become familiar with the major parts of the microscope & their functions

- to be able to prepare & examine a slide

1.Obtain a compound microscope (sometimes called a light microscope ) and study figure 2.1to learn the names of its major parts.Note that the lens system of a compound microscope includes three parts - the condenser, objective lens, and eyepiece.

2.Match the names of the microscope parts with the description.Place letter of your choice In the space provided.

_____increases or decreases light intensityA. arm

_____platform that supports microscope slideB. condenser

_____concentrates light onto specimenC. field of view

_____causes objective lens to move upward or downwardD. nosepiece

_____produces magnified image of specimen in body tubeE. slide clip

_____holds microscope slide in positionF. adjustment knob

_____magnifies real image of specimenG. eyepiece lens

_____serves as a handle for carrying microscopeH. iris diaphragm

_____part to which objective lenses are attachedI. objective lens

_____circular area seen through eyepieceJ. stage

Magnification:The magnification of each lens is fixed and inscribed on the lens.The ocular lens usually has a 10x magnification. The powers of the objectives may vary, but are usually 4x, 10, 40x .The total magnification is calculated by multiplying the power of the ocular lens by the power of the objective lens.

Assignment 1

1.Obtain a microscope slide and cover slip.If they are not clean, wash them with soap & water, rinse and dry them.Use a paper towel to dry the slide, but use Kim wipes to blot the water from the fragile cover slip.

2. Using scissors, cut three letters from a newspaper, with the letter ‘I’as the middle letter. 

3.Prepare a wet mount slide of the letters.- place a drop of water on a clean slide.

- place letters in the drop of water. - place one edge of cover glass against the slide so that the cover slip touches the water drop.- lower cover slip gently onto the slide.Use a paper towel to soak up any excess water.If too little water is present, add a drop at the edge of the cover slip and it will flow under the cover slip.

4.Place the slide on the microscope stage, with the letters over the stage aperture, the circular opening in the stage.Secure the slide.

5.Rotate the 4x objective into viewing position & bring the letters into focus.Center the ‘I’and bring it into sharp focus.Can you see all of the ‘I’?Can you see other letters?What is different about the orientation of the letters when viewed with the microscope instead of the naked eye?

6.Move the slide to the left while looking through the ocular.Which way does the image move?Practice moving the slide while viewing through the ocular, until you can quickly place a given letter in the center of the field.

7.Center the ‘I’ and bring it into sharp focus.Rotate the 10x objective into viewing position.Is the ‘I’ centered and in focus?If not, center it and bring it into sharp focus.How much of the ‘I’ can you see?

8.Rotate the 40x objective into position.Is the ‘I’ centered and in focus?All that you can see at this magnification are ‘ink blotches’ that compose the ‘I’.If you do not see this, center the‘I’ and bring it into focus with the fine-focusing knob.Never use the coarse - focusing knob with the high-power objective.

9.Practice steps 5 - 8 until you can quickly center the dot of the letter ‘I’and bring it into focus with each objective.Remember, you are never to start observations with the high-power objective.Instead, start at a lower power and work up to the 40x objective.

10.Remove slide and clean.

Assignment 2

1.Prepare a wet-mount slide of two crossed hairs, one blond and the other brunette.Obtain hair from cooperative classmates.

2. Using the 4x objective, center the crossing points of the hairs in the field and observe.Are both hairs in sharp focus?

3.Examine the crossed hairs at 100x magnification.Are both hairs in sharp focus?Determine which hair is on top by using focusing technique.If you have trouble with this, see your instructor.

4.Examine the crossed hairs at 400x magnification.Are both hairs in focus?Move the crossing point to one side and focus on the blond hair.Using focusing technique, observesurface and optical midsection views of the hair as shown in figure 2.8.

5.Remove slide and clean.

6. Turn off microscope, carefully wrap cord, put dust cover on, and return to locker.