SNC1DE
1.2 Using the Microscope Lab
Name _________________________________________
Partner ________________________________________
BACKGROUND
The microscope is a very important scientific tool. It allows you to observe things that are much too small for the eye to
see alone. With some instruction and a little practice, you can learn how to operate a microscope and investigate an
exciting, new, miniature world.
There are a number of kinds of microscopes used for special purposes. You may have heard for example, of the electron
microscope or the phase-contrast microscope. You will use a compound microscope in your laboratory activities.
This optical instrument works by means of transmitted light. The parts of the microscope are arranged to guide and
control a beam of light rays. The beam passes first through the specimen being examined and then through a system of
lenses. When you look through the top lens of the microscope, the beam of light enters your eye. You see the object
magnified because the lenses spread the light rays apart after they have passed through the specimen being viewed. Any
object to be viewed through a compound microscope must be thin enough for light rays to pass through it.
OBJECTIVES
In this activity you will:
1.
2.
Become familiar with the parts and operation of a compound microscope.
Learn to prepare and observe wet mounts.
MATERIALS
Microscope
Slides
Cover slips
Lens paper
Dissecting needle
Sheet of newspaper
Water
Pipette
Magazine picture in color
Hairs of different color
Ruler
Pieces of very thin cloth
Scissors
Paper towels
PROCEDURES
Part I. Learning about the Microscope
a.
b.
c.
d.
e.
f.
Obtain your microscope from your teacher. Carry it with one hand holding the arm and the other supporting the base, as
shown in Figure 1. Set it down away from the edge of the table.
Compare your microscope with Figure 2. Learn the functions of each part of the microscope.
Some microscopes have built-in electric light, or illuminator. Some have a mirror to reflect light onto the specimen. If
you have a mirror, note that its angle is widely adjustable. Learn to direct the reflected light upward through the
microscope by slanting the face of the mirror correctly. Look through the ocular as you adjust the mirror to obtain the
maximum amount of light on your specimen.
Examine the diaphragm. Adjust it to the largest opening so that the most light enters the microscope. You can tell this by
looking through the ocular.
Place a slide on the stage and fasten it with the stage clips. Place your two thumbs on the corners of the slide nearest you
and your forefingers on the corners farthest from you. Practice moving the slide back and forth on the stage.
Carefully rotate the nosepiece. You can hear and feel a click as an objective is snapped into place.
The low-power objective is shorter than the high-power objective. The magnifying power of each objective is engraved
on its side. This tells how many times an object is magnified when observed through the lens.
OBSERVATIONS
1.
Locate the low-power objective.
What is its magnifying power? _____________________________
2.
Locate the high-power objective.
What is its magnifying power? _____________________________
If the lenses look dirty or smudged, carefully wipe them with lens paper. Use only lens paper because other kinds of
paper can damage the lenses.
The ocular lens also has a magnifying power. The total magnifying power of the microscope is easy to calculate. Simply
multiply the magnifying power of the ocular by the magnifying power of the objective being used. For example, if the
ocular is 5 x and the objective is 10 x, the total magnification of the object being viewed is 5x10=50x.
3.
Examine the ocular lens. What is its magnifying power? _______________________________________
4.
What is the total magnification produced when the low-power objective is used? Show your calculations.
5.
What is the total magnification produced when the high-power objective is used? Show your calculations.
Carefully turn the coarse adjustment knob, and observe the movement it produces.
6.
Which part of your microscope moves when you turn the coarse adjustment?
_____________________________________________________________
7.
Turn the fine adjustment knob, and closely observe the movement it produces. (The motion may be difficult to see.)
8.
How do the effects of the coarse adjustment and fine adjustment differ?
Part II. Preparing and Examining a Wet Mount
You can make a temporary slide, or wet mount, to examine a specimen under the microscope.
a.
b.
c.
d.
e.
f.
g.
h.
i.
1.
Find a small letter "e" in some newsprint. Cut a 1-cm square with the "e" near the center.
Place the square in the middle of a clean slide. With a pipette, put 1 drop of water on the square. Drop the water from
about 1 cm above the slide. Do not touch the pipette to the paper or it will stick.
Now cover the mount with a clean cover slip. One way to do this is shown in Figure 3. Hold the cover slip at about a 45°
angle to the slide and move it toward the drop. As the water touches the cover slip, it will spread along the edge. Gently
lower the cover slip into place. Another way to put the cover slip into place is to support the cover slip with a dissecting
needle, as shown in Figure 4. Slowly lower the supported edge and watch as the water fills the space. Use whichever
method is easier for you and gives you a good wet mount. Do not press on the cover slip-it should rest on the top of the
water. A good wet mount is free of bubbles. If your mount has too many bubbles, take off the cover slip and absorb the
water with a paper towel. Then repeat steps b and c.
Put your microscope in an upright position with the stage horizontal, not tilted. (Always have the microscope in this
position when you are using a wet mount.) Make sure the diaphragm is at the largest opening.
Click the low-power objective into place. Make sure you have a good light source. Look through the microscope and
adjust the mirror or illuminator to give the brightest light. (Remember never to use direct sunlight as a light source.)
Check to be sure the bottom of the slide is dry before placing it on the stage of the microscope. Set it on the stage so that
the "e" is in reading position and over the hole in the stage. Fasten the slide with stage clips.
Look at the body tube from the side. Use the coarse adjustment knob to lower the body tube until the objective is about
1/2 to 1 cm above the slide, or until you feel the automatic stop.
Look through the ocular, keeping both eyes open. Keeping both eyes open is difficult at first, but it helps to prevent
eyestrain. It will become easier with practice.
Then slowly raise the body tube by turning the coarse adjustment knobs. Raise it until the letters come into focus.
Observe the letter "e."
Draw the letter "e" the same size and with the same texture and in exactly the same position as you see it through the
microscope under Low Power
Total Mag.= ________________________
2.
Move the slide to the left.
Which way does the image move? ___________________________
3.
Move the slide to the right.
Which way does the image move? ___________________________
4.
Move the slide backward and forward.
5.
Observe the wet mount as you change the diaphragm to each of its settings. Adjust it to give good contrast and
illumination without glare.
Which ways does the image move? ___________________________
What does the diaphragm control? ______________________________________
Before using high power, the specimen must be in sharp focus in the center of the low-power field of view. All focusing
under high power is done with the fine adjustment knobs. Remember that there is no automatic stop for the high power
objective.
6.
Watching from the side, carefully switch to the high-power objective. Make sure that the objective does not hit the slide,
but expect it to be very close.
7.
Focus on the letter "e." Only a slight turn of the fine adjustment knob will be needed to do this.
1.
Draw the letter "e" exactly as you see it under High Power.
Total Mag. = _________________________
2.
Is the field of view larger under high power or low power? ___________________
3.
Compare the brightness of the field under high power and low power.
High Power
Low Power