1) In which one or more of the following situations does the image contrast equa
ID: 2305602 • Letter: 1
Question
1) In which one or more of the following situations does the image contrast equal 25%?
Image point = intensity of 5; background point = intensity of 20
Image point = intensity of 80; background point = intensity of 100
Image point = intensity of 1000; background point = intensity of 800
Image point = intensity of 20; background point = intensity of 25
Image point = intensity of 1250; background point = intensity of 1000
Image point = intensity of 100; background point = intensity of 80
2) Finish the following statement with one or more of the phrases below to make it TRUE.
“The probability of electron scattering from a finite region of a specimen depends on … “
the density of the specimen in that region.
the overall thickness of the specimen in that region.
the objective lens aperture.
the focus setting of the objective lens set by the microscopist.
the mass thickness of the specimen in that region.
3) TEM offers several advantages over light microscopy (LM) for studying biological specimens. They include which one or more of the following: (answer all that correctly apply but credit will be deducted for wrong answers). BEWARE: some statements may be true and others false, but this is NOT a true/false question.
TEMs are much more expensive than LMs
TEMs are much easier to operate than LMs
TEM images can be formed over a much larger range of magnifications than images in a LM.
TEM can generally be performed in real time and continuously on living cells and tissues
Biological specimens are very sensitive to the electron beam in the TEM, but very insensitive to photons used in the LM
Higher resolution can be achieved in TEM images compared to LM images
a.Image point = intensity of 5; background point = intensity of 20
b.Image point = intensity of 80; background point = intensity of 100
c.Image point = intensity of 1000; background point = intensity of 800
d.Image point = intensity of 20; background point = intensity of 25
e.Image point = intensity of 1250; background point = intensity of 1000
f.Image point = intensity of 100; background point = intensity of 80
Explanation / Answer
1) image contrast can be found by the following formula:
|I-Ib|/Ib where I is image intensity, Ib is background intensity.
a. contrast=|5-20|/20=15/20=0.75=75%
b. contrast= |80-100|/100=20/100=0.2=20%
c. contrast= (1000-800)/800=0.25=25%
d. contrast=|20-25|/25=5/25=0.2=20%
e. contrast=(1250-1000)/1000=250/1000=0.25=25%
f. contrast=(100-80)/80=20/80=0.25=25%
answer= c,e,f
2) answer= a,e
3) answer=b,c,f
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