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Problem Set 3.1: Microscopes Instructions: Read
pages 308 to 326 in your text and answer the questions that follow. |
1. What do spectacles, microscopes, and
telescopes have in common?
All have lenses used to focus light and images. All can be used
to magnify images.
2. Why was the discovery of glass important
for progress in science?
Glass is transparent and allows light through it. Glass can
refract light to focus images.
3. How did Anton van LeeuwenhoekÕs
microscopes differ from those used by most other microsocopists at that time?
Early microscopes were often flawed. LeeuwenhoekÕs microscopes
used only a single small lens
rather than multiple lenses.
4. Who was the first person to apply the
word ÒcellÓ to the many similar tiny subunits of a specimen that can be seen
with a microscope? How do we use this term today?
Robert Hooke first used the term cell since the images of
magnified cork reminded him of small
rooms in a building (cellula = small room in Latin). Today, the
term cell refers to the smallest
separate unit of living organisms.
5. In what way is the enlarged version of an
object seen with a magnifying glass similar to a photograph and what ways are
they different?
They are the same because show the same enlarged details of the
object with their natural colors.
They are different because the imgae is inverted and backwards.
6. Compare the location and the function of
the objective and ocular lenses.
Ocular lens is located at the eyepiece and magnifies a small
amount. The objective lenses are
located just above the stage and are responsible for greater
magnification.
7. a) How do you change from one objective
lens to another?
Rotate the revolving nosepiece.
b)
From what position should you look at while doing this?
Looking through the ocular.
c)
Which objective lens should be in place when you put the microscope away?
The lowest power.
8. Describe the proper procedure for
carrying a microscope.
Use two hands, one placed below the microscope supporting the base
and the other holding
the arm.
9. Why should you not touch microscope
lenses with your fingers or wipe them with anything but lens paper?
Particles of dirt can scratch the lenses, even those particles
found on clean skin!
10. What is the Òworking distanceÓ of a
microscope? How is it related to producing a clear (focused) image of the
specimen?
The working distance is the distance between the objective lens
and the specimen. By changing
the working distance, the image is brought into focus (use
adjustment knobs to change this)
11. As you move from low to medium to high
power, how does each of the following change:
a)
the size of the field of view?
The size of the field of view gets smaller (less area of
specimen is seen)
b)
the illumination?
The illumination is less.
c)
the depth of field?
The depth of field is decreased (less thickness of image is in
focus at one time)
12. What is resolving power?
The resolving power is the ability of the microscope to show
separate objects as distinct.
13. What is the difference between the
resolving power of our eyes and that of a microscope?
The resolving power of our
eyes is about 0.1 mm (i.e. we can distinguish objects as distinct if they
are 0.1 mm or larger) while
light microscopes are capable of resolving objects that are 0.0002 mm
in size.
14. How are resolving power and magnification
related to each other?
The resolving power and
magnification are equally important. However, at higher magnifications
Images may be blurry and useless unless the microscope has a
good resolving power (to
distinguish details of the object that is being examined).
15. What is the main difference between a
light microscope and an electron microscope?
A light microscope uses
light to examine images and can
magnify to a maximum of about 1500X.
An electron microscope uses
a beam of electrons to examine images
and can magnify to a
maximum of about 250 000X.