Microscopy - Midterm 1

Question 1

How does light travel? in bright field microscopy ?

Answer 1

Light source -> substage condenser -> stage -> objective lens -> ocular lens

Question 2

How does light travel in phase contrast microscopy?

Answer 2

Light source -> annular stop -> substage condenser -> stage -> objective -> phase plate -> focal plane -> ocular lens

Question 3

What happens when you have too little light?

Answer 3

you get reduced clarity

Question 4

What happens when you have too much light?

Answer 4

you get reduced contrast

Question 5

What is resolution?

Answer 5

Ability of microscope to clearly distinguish two very small objects that are placed very close together as two separate entities

Question 6

What is object?

Answer 6

the material that is being examined

Question 7

What is image?

Answer 7

what you see with your eyes

Question 8

What is field?

Answer 8

area on the slide that is being viewed

Question 9

Total magnification is equal to

Answer 9

Objective x ocular (ocular is always 10)

Question 10

What does parfocal mean?

Answer 10

when the specimen is in focus at one magnification, it will be in focus at other magnifications, requiring only minor adjustments to the stage level

Question 11

Greater resolution =

Answer 11

the closer something can be and still be distinguished as two different things

Question 12

What is the limit of resolution?

Answer 12

smallest distance between the two objects that will still allow them to be viewed as 2 separate objects.

Question 13

Average light microscope has a limit resolution of what?

Answer 13

0.2 micrometer. therefore, bacterial cells of 0.5 micrometer diameter can still be viewed as separate.

Question 14

What is a condenser diaphragm?

Answer 14

Works like the iris of the eye and controls the amount of light that enters

Question 15

What happens when you open the diaphragm?

Answer 15

you increase the amount of focused light –> this increases clarity but decreases contrast

Question 16

What happens when you close the diaphragm?

Answer 16

Decreasing the amount of focused light –> increasing the contrast but decreasing the clarity

Question 17

True or false? Its good to use the diaphragm to control the intensity or brightness of light

Answer 17

False, it reduces the resolution

Question 18

What is annular stop? What happens to light there?

Answer 18

Ring with an opaque center that blocks light in the center. this produces a hollow cylinder of lightThere is no phase shift or angle change

Question 19

What happens when light passe through substage condenser after the annular stop?

Answer 19

there is a change in angle in the light as it bends to form a hollow cone shape. There is no change in phase

Question 20

What happens the light when it hits the object?

Answer 20

The light that hits the cells gets diffracted and changes angle, they also change phase by -1/4 lambda
The light that hits the medium doesnt experience any change in phase shift or angle

Question 21

What happens when light hits the phase plate?

Answer 21

The diffracted light that hits the cells are now passing through the clear center of the ring of the phase plate
The light that wasnt defracted in the medium will hit the ring of the phase plate causing it to phase shift to +1/4