The compound microscope Flashcards
The smallest object that the eye can see at a distance of 250
mm is about
0.07-0.14mm
Two general categories of microscope
- Light Microscope
- Electron type microscope
Uses light waves and lenses that are associated with the light microscope
Light Microscope
employs electron beams and magnetic fields to produce the image.
Electron type microscope
Light microscope magnify objects only up to?
300X
employs two separate lenses, an ocular and an objective, in order to achieve 2-5 times greater
magnification.
Compound type microscope
where the microscope field is brightly lighted and the object to be observed appears dark die to its ability to absorb or refract some of the incident light
bright field
where the object appears luminous against a dark background since it reflects some of the incident light in all directions
dark-field
allowing greater resolution and magnification. It is used principally to detect or even measure substances in specimens of living tissues that are known to absorb UV light at particular wavelengths. UV is not visible to the eye, so the image formed is recorded with the use of cameras or a television screen.
Ultraviolet (UV)
UV is not visible to the eye, so the image formed is recorded with
the use of?
Cameras or television screen
which makes use of the property of certain chemical substances that
release light at a different wavelength when exposed to UV rays. Such substances convert UV light into visible waves of greater length.
Fluorescent
Bacteria and other microorganisms are stained with __________ that can be detected in a microscope illuminated with UV light.
fluorescent stain
utilizes the refraction that occurs when light passes from one medium into another of different density. The special objectives and condenser intensify slight differences in contrast produced by this bending of light.
phase-contrast
It is useful in studying the internal structures of microorganisms because structures differing in refractive index from the surrounding protoplasm become
visible, and their sizes and locations can be determined.
phase-contrast
keeps the microscope steady at any position of the stage
base
fastened to the base through the inclination joint, permits the adjustment of the stage to a desired angle
arm
reflects the light into the condenser
concave
concentrates the light rays received from the mirror and sends them to the objective
condenser
is a horizontal platform upon which the specimen to be examined is placed. At the center of the stage is a circular aperture
stage
hold the slide in place on the stage
stage clips
is that part of the optical system of the microscope which produces the specimen’s initial magnified image (real) within the body tube
objective
Three objectives of the microscope
- Low power
- High power
- Oil immersion
The objectives are _______that is, they are corrected for the spectral colors of red and blue.
achromatic
an optical constant of the lens system, is the distance from the center of the lens to the point where parallel rays entering the lens are brought to a focus.
Focal length
that property to recognize features of a specimen that are close to each other as separate or distinct.
Resolving power
The greater the resolving power,?
The greater the definition of an objective
This property is dependent on the wavelength of light used and an optical property of the objective lens known as a numerical aperture.
Resolving power
is a measure of the resolving power of an objective. An objective with a 0.25 N.A. allows the viewer to distinguish as separate 25,000 lines per inch.
Numerical aperture (N.A)
Lenses with higher magnification usually have higher N.A. but the medium through which the
light passes also affects N.A.
T/F
True
means that the objectives are optically ad mechanically designed so that the distance between the specimen and the aerial image is always constant.
Parfocal
___________________________ is sufficient to restore critical sharpness of the image after changing from one objective to another, thus, the coarse focus knob need not to be operated.
Slight refocusing with the aide of the fine focus knob
to which parfocal objectives are attached, allows convenient
shifting of the objectives
revolving nosepiece
is a hollow cylindrical tube through which light passes from the objective to the eyepiece
body tube
The upper portion of the body tube is called the ______________
draw tube
that part of the optical system through which the specimen is viewed.
eyepiece or ocular
The intermediate image projected by the objective is enlarged by the______________
eyepiece
The term compound microscope is derived from?
from the fact that the specimen is magnified twice, first by the objective and second by the eyepiece
The final image formed is called?
virtual image
The magnification of the compound microscope is, therefore, the product of the
magnifying power of the objective and the eyepiece.
If the magnifying power of the objective is 100X and the eyepiece is 10X, the total magnification will be
1000X
The _____________________ knob is used to bring the objective into approximate focus. For maximum
definition, the ____________________ knob is used.
Coarse focus; fine focus knob
What comprise the optical system?
The mirror, the condenser, the objective and the eyepiece
The __________________________ has a much greater depth of focus and is
generally used for initial focusing and viewing.
low power objective
the higher the magnification of the objective, the larger the working distance. T/F
False; smaller working distance
The free space between the specimen surface and the objective is the?
working distance (mm)
The higher the power of the
objective, the lesser is the area of the specimen surface included in the field of vision. T/F
True
If a sharp image is not obtained despite the application of the above procedure, it is possible that:
The fine focus knob has reached a stop. On the right side of the microscope at the
rack and pinion area are three lines. Center the line (located on the fine focus knob side) between the two lines (located below the coarse focus knob) by turning the fine focus knob.
Focusing attempts are too rapid. Use the fine focus knob and adjust slowly.
The objective is covered with dried oil from previous use. Under the supervision of your instructor, remove the dried oil with xylene or 95% ethanol and dry the
lens right away.
The cover slip is too thick. The optimum thickness is 0.17 mm.
The slide is inverted.
After using the oil immersion objective:
Blot out the oil with lens paper
Clean the lens with lens paper wet with xylol (do this under the instructor’s supervision)
Blot-dry the lens with fresh lens paper
Microscopic objects can be measured by means of an ocular micrometer or a ___________
Filar micrometer
The unit of linear measurement in microbiology is the micrometer (µm), which is equivalent to _________________
1/1000 mm or 1/25,400 inch
is a glass disc with mounted scale. It may or may not have numbers on it. It is inserted into the eyepiece and must be calibrated for the particular objective, eyepiece and tube length before measurements are made. The
student microscope has a fixed tube length.
ocular micrometer
is a glass slide with graduations of known intervals
stage micrometer
Some micrometers have numbers to indicate the _________________
length of the divisions
Which is a bigger division, 0.01 mm or 0.1mm
0.1mm
