Light and Refractive Index

Question 1

what are the goals of microscopy?

Answer 1

• magnification (produce a magnified image of the specimen)
• resolution (separate details in the image)
• contrast (render details visible to the detector)

Question 2

electric field and magnetic field vibrate in __________ planes as they propagate forward.

Answer 2

perpendicular

Question 3

what is specular reflection?

Answer 3

smooth surface maintains coherence and reflects

Question 4

what is diffuse reflection?

Answer 4

rough surface scatters light

Question 5

what are plane waves?

Answer 5

when waves of light spread out from their original tight circles to form straightened waves where all photons hit something at the same time

Question 6

what types of images do convex and concave lenses make?

Answer 6

convex = real image (projected into space); converge light; projected on opposite side of object inverted
concave = virtual image (have to look through lens to see); diverge light; appears upright on same side as object

Question 7

what is Snell’s law and what does it say?

Answer 7

n1sinθ1 = n2sinθ2
- when going from a high RI medium into a low RI medium, the ray is bent AWAY from normal

Question 8

if the incident angle is greater than the critical angle, the ray will be …

Answer 8

internally reflected

Question 9

what is dispersion?

Answer 9

change in RI with wavelength; lower value, the more dispersion

Question 10

what is magnification?

Answer 10

m = q / p
p < q = object distance < image distance

Question 11

what is spherical abberation?

Answer 11

• optical-path dependent distortion (blurry)
• rays at perimeter converge closer than center rays
• correct through correct thickness of cover glass

Question 12

what is chromatic aberration?

Answer 12

dispersion causes wavelengths to separate (different wavelength, different RI)

Question 13

what is curvature of field?

Answer 13

flat object perceived to be a curved object

Question 14

what is image distortion?

Answer 14

• when magnification is not constant across field of view
• if magnification decreases with distance from the center = barrel
• if magnification increases with distance from the center = pincushion

Question 15

what does Kohler illumination do?

Answer 15

• produces even lighting of the specimen
• reduces unwanted diffraction, light scattering, and glare from optical surfaces within microscope

Question 16

what are the fundamental actions of Abbe’s Theory of Image Formation?

Answer 16

• diffraction that occurs by the specimen
• collection of the diffracted orders by the objective
• interference of these orders to produce the image (by eye or captured)

Question 17

what causes light and dark bands?

Answer 17

diffracted beams of light that cause destructive (dark) and constructive (light) interference

Question 18

what causes contrast?

Answer 18

interference between the 0th and highest order of diffracted rays in the back focal plane of the objective

Question 19

finer details diffracts light over _______ angles.

Answer 19

larger

Question 20

how is wavelength related to resolution?

Answer 20

shorter wavelength, greater resolution

Question 21

what is numerical aperture (NA)?

Answer 21

• measure of the light gathering ability of a lens
• higher the NA, the better
  NA = n (sinμ)

Question 22

when are two object points resolved according to Rayleigh?

Answer 22

when the central diffraction spot of one point coincides with the first diffraction minimum of the other point in the image plane

Question 23

what is empty magnification?

Answer 23

when an image is magnified but no additional features have been resolved (bigger but blurry)

Question 24

define approximate useful magnification?

Answer 24

• multiply objective by eyepiece
• needs to fit between 500 x NA and 1000 x NA

Question 25

what is the approximate useful magnification if the objective = 100x (NA = 1.42) and eyepiece = 10x?

Answer 25

magnification of objective x eyepiece = 100 x 10 = 1000
minimum = 500 x 1.42 = 710
maximum = 1000 x 1.42 = 1420
since 1000 is between 710 and 1420, its good

Question 26

what is incandescence?

Answer 26

emission of electromagnetic radiation as a result of high temperature

Question 27

what is a black-body radiator?

Answer 27

theoretical “perfect” radiator, emitting light over all wavelengths of EM spectrum; wavelengths of BBR only depend on temperature

Question 28

what does a condenser do?

Answer 28

• controls contrast
• minimizes/eliminates “stray light” by reducing glare and contrast
• focuses the image of field diaphragm
• must match NA of condenser to that of the objective to achieve maximum resolution

Question 29

what does an open condenser do?

Answer 29

decreases contrast but increases resolution

Question 30

what is the most common type of condenser?

Answer 30

• Abbe-type (simple two-lens, inexpensive, not corrected, good for routine work)
• other type is swing out (more lenses, higher NA)

Question 31

what are the three types of condensers? which one is the best?

Answer 31

achromat (worst) , fluorite, and apochromat (best)

Question 32

how is magnification related to depth of field and wavelength?

Answer 32

increased magnification, increased depth of field, decreased wavelength

Question 33

how is magnification related to working distance?

Answer 33

increased magnification, decreased working distance

Question 34

what differentiates glass from other substances?

Answer 34

it is an organic product of fusion that has solidified without crystallization

Question 35

how crystalline quartz different from amorphous glass?

Answer 35

• crystalline quartz = cooled slowly; breaks along straight lines
• amorphous glass = cooled rapidly; random orientation of molecules and random breakage; stronger than quartz

Question 36

what are formers in glass? name an example

Answer 36

• compounds that, when cooled quickly after melting, will solidify w/o crystallization
• SiO2

Question 37

what are fluxes in glass? name an example

Answer 37

• used to lower melting temperature of glass
• Na2CO3 (soda ash)

Question 38

what are stabilizers in glass? name an example

Answer 38

• used to impart chemical resistance and strength to glass
• CaO

Question 39

what are the steps of glass manufacturing?

Answer 39

1) raw materials
2) melting
3) forming (shaping)
4) annealing (controlled cooling in lehrs)
5) secondary processing (cut, polished, etc.)

Question 40

what is the most common type of glass?

Answer 40

soda-lime

Question 41

what is boro-silicate glass and what is it used for?

Answer 41

• add >5% boric acid
• provides low thermal expansion and better resistance to acid corrosion
• used in lab glassware and cookware

Question 42

what is alumino-silicate glass and what is it used for?

Answer 42

• add greater % of aluminum
• provides greater heat tolerance than boro-silicate glass and resistant to alkalis
• used in lab glassware and cookware

Question 43

what is lead-alkali-silicate (AKA leaded) glass and what is it used for?

Answer 43

• high RI and dispersion
• easier to shape
• used in crystal tableware, neon sign tubing, jewelry, etc.

Question 44

what is silica glass and what is used for?

Answer 44

• made from molten quartz (costly and difficult to manufacture)
• ONLY used in specialized applications

Question 45

how is flat glass made?

Answer 45

drawn through rollers in float process (glass flows onto bed of molten tin - makes one side fluoresce)

Question 46

how is container glass made?

Answer 46

molding process (pressed, blown, cast, or spun into shape of mold)

Question 47

how are glass fibers/fiberglass made?

Answer 47

drawn into filaments by rotary process similar to cotton candy makers