WarmUp 8/31/09 – Copy and
answer in notebook
1. What is the name of the Red objective lens? Blue?
Yellow?
2. What is the magnification of each?
3. What is the total magnification when looking through
each of the following:
scanner? Low Power? High Power?
4. How does what you see change as you increase in
magnification? (2 ways)
5. How does the orientation of objects appear under the
microscope compared to your naked eye?
6. What part of the microscope should never be used
with the high power lens?
7. What term is used to describe the “circle of light” you
see when looking through the ocular?
Need to Know!
– # of microns or
micrometers in a
millimeter
– Volume of a block
– Area of a circle
– Volume of a cylinder
1000 µ
L x W x H
π r2
H π r2
CALCULATING SIZE
OF MICROSCOPIC
OBJECTS
SCANNER OBJ. LENS
4X -------- > 40X
__?____ = diameter of the field of
view
4 mm DIAMETER
1 mm = 1000 micrometers
4 mm = 4000 micrometers
4000 micrometers = 4000 μ
LOW POWER
100 X
2 mm
2000 micrometers (μ)
LOW POWER
100 X
1/5 F.O.V. = 1/5 of 2000 μ
2000 μ / 5 = 400 μ
HIGH POWER
400 X
f.o.v.????
?
Low to high = 100x to 400x
4 times closer!
See only ¼ as much!
¼ of 2000μ = 500 μ
F.O.V. = 500 μ
HIGH POWER
400 X
Same Object
4/5 F.O.V. = 4/5 of 500 μ
400 μ !
Same object = Same Size!
HIGH POWER
400 X
1/5 of 500μ = 100μ
LOW POWER
1/10 of 2000μ = 200μ
HIGH POWER
1/10 of 500μ = 50μ
Mathematically!
• 100x --- > 400 x
increases by 4 times
• But, you only see __________ as much!
• One-fourth!
So, f.o.v. or object on high power is ¼ that of
low power!
ocular = 10x
low power objective = 20x
high power objective = 40x
The picture shows the low power field of view for the microscope with
the lenses listed above.
a) What is the approximate size of the cell in micrometers ?
b) What would be the high power field of view ?
c) How many cells like the one in the picture could fit in the
high power field of view ?
a). 500 micrometers
First, we have to visualize how many of those cells could fit across the
field --- about 4. So 2 mm (the width of the field) / 4 = .5 mm, which
converts to 500 micrometers.
b). 1000 micrometers
The ratio of low to high power for this scope is 20/40, or 1/2. So we
will see 1/2 of the low power field under high power. 1/2 x 2 mm =
1mm, which converts to 1000 micrometers.
c). 2 cells
Again the ratio of low to high power is 20/40, or 1/2. If we can
see 4 cells across the low field of view we will see 1/2 as many
in the high field of view. 1/2 x 4 = 2 cells.