Optical Properties

Question 1

what are transparent, translucent and opaque materials, respectively?

Answer 1

transparent: see through
translucent: let light through
opaque: doesn’t let any light through

Question 2

what are optical properties?

Answer 2

a materials response to exposure to electromagnetic radiation especially to visible light

Question 3

what are the 2 things light can behave as?

Answer 3

a particle or a wave

Question 4

what is a photon

Answer 4

a quantum unit of light

Question 5

what do the variable “E”, “v”, “h” and “c” represent respectively

Answer 5

energy of a photon, frequency, planck’s constant, speed of light in a vaccum

Question 6

radiations are packets of energy known as what?

Answer 6

photons

Question 7

if light is transmitted, what will happen to the electron cloud?

Answer 7

the cloud will distort in shape

Question 8

which is greater, the velocity of light in a material or vacuum

Answer 8

vacuum

Question 9

if we add large ions to glass, what happen to the speed of light through the glass

Answer 9

it will decrease

Question 10

if phi(0)>phi(c), what is the case

Answer 10

light is totally internally reflected

Question 11

how do you determine the critical angle

Answer 11

its when phi(2) is 90deg

Question 12

why are fiber optic materials cladded in low n material

Answer 12

so that the light will be totally internally reflected

Question 13

what can be said about the size of the distance between energy states in metals

Answer 13

its very small

Question 14

what does the small size of the energy gap in metals mean in terms of absorption

Answer 14

it means almost any frequency of light can be absorbed by metals

Question 15

true or false, almost all light coming into a metal is absorbed within 0.1 micrometers of the surface

Answer 15

true

Question 16

what types of materials can electrons be absorbed by

Answer 16

metals and small band gap materials

Question 17

what types of materials can nuclei be absorbed by

Answer 17

all

Question 18

what is the energy lost in absorbtion light by metals lost as?

Answer 18

the remaining energy is lost as phonons

Question 19

why are metals reflective

Answer 19

because the energy lost by a descending electron is the same as the incident one

Question 20

when an electron transitions from excited state, what is emitted

Answer 20

a photon

Question 21

what does the color of reflected light depend on

Answer 21

the wavelength

Question 22

true or false, metals are more transparent to very high energy radiation, like X-rays and gamma-rays

Answer 22

true

Question 23

what can be said about an amorphous polymer in terms of scattering of light

Answer 23

very little to no scattering

Question 24

If a polymer is transparent, what can be said about its strucutre

Answer 24

it will be an amorphous polymer

Question 25

what can be said about an semi-crystalline polymer in terms of scattering of light

Answer 25

they scatter light a little

Question 26

where does scattering of light occurs

Answer 26

at boundaries

Question 27

highly crystalline polymers will be what

Answer 27

opaque

Question 28

if a polymer goes from being amorphous to drawn what can be said about its optical properties

Answer 28

it becoming increasing crystalline, therefore it will become increasingly opaque

Question 29

for non-metals, what has to be the case for light to be absorbed

Answer 29

hv

Question 30

if a semiconductor appears as metallic, what does this mean?

Answer 30

the visible photons were all reflected

Question 31

what it the relationship between the impurities and the aborption

Answer 31

more impurities=more absorption

Question 32

how does an increase in impurities cause an increase in absorbtion

Answer 32

impurities divide up the band gap to allow transitions with less energy than Egap

Question 33

how is the color of nonmetals determined

Answer 33

by the sum of the frequencies of the 1. transmitted light and 2. the remitted light from the electron transitions

Question 34

how can an image become blurred

Answer 34

if the transmitted light is scattered internally

Question 35

what are 3 factors that cause scattering?

Answer 35

1. grain boundaries 2. pores in ceramics 3. different phases in materials

Question 36

what is luminescence

Answer 36

the reemission of light by a material. material absorbs light at one frequency and reemits it as another

Question 37

how is phosphorescence achieved

Answer 37

if the resting time in the trapped state is relatively long (>10^-8 seconds)

Question 38

what is photo luminescence?

Answer 38

as electrons fall back to their ground states, UV light is emitted

Question 39

how are colored lamps made?

Answer 39

by lining the inside of the tube with a material that only absorbs UV and re-emits visible light

Question 40

how can we dictate the color of these "colored lamps"

Answer 40

by doping with various metal cations

Question 41

what is cathodoluminescense

Answer 41

- the inside of a tube is coated with a phosphor material. - the phosphur is bombarded with electrons - the electrons in phospur are excited to higher levels - visible light is emitted as electrons drop to lower ground states

Question 42

what does the color of light depend on in cathodoluminescense

Answer 42

the composition of the phoshur

Question 43

what can be said about the direction of the light that is emitted in cathodoluminescense

Answer 43

its random in phase and direction

Question 44

how is total internal refraction made possible in fiber optic cables

Answer 44

by a specific difference in the indicies of refraction of the cladding and the core

Question 45

what is the problem with the step index design

Answer 45

the different light rays travel different distances and reach the end at different times, limiting data communication

Question 46

what design of index was created to rectify the problem

Answer 46

the graded-index

Question 47

how is this design achieved

Answer 47

by parabolic doping

Question 48

how does the graded-index design fix the problem

Answer 48

becuase the rays travelling in the outer regions are going through lesser indicies of refraction therefore they travel faster (according to V=C/n), making them arrive at the same time

Question 49

if the emitted light has the same energy and phase as the incident light, what is this called

Answer 49

coherent