waves P2

Question 1

monochromatic light

Answer 1

light of a signal wavelength and fequency and so a single colour

Question 2

not using monochromatic coherent light

Answer 2

if you dont use it pattern produced wont be very clear, e.g. use of white light

Question 3

coherence

Answer 3

same wavelength and frequency and a fixed phase difference between them

Question 4

single slit experiment

Answer 4

laser beam shone through very narrow slit, if wavelength of light is roughly the same size as the slit you get a diffraction pattern of light and dark fringes

Question 5

single slit experiment pattern

Answer 5

bright central fringe (central maximum)
with alternating dark/ light fringes either side
fringe pattern due to interference

Question 6

bright fringe

Answer 6

constructive interference. arrive in phase

Question 7

dark fringe

Answer 7

total destructive interference arrive completely out of phase

Question 8

white light

Answer 8

mixture of different colours each with a different wavelength

Question 9

colour/ wavelngth scale
biggest to smallest

Answer 9

red
orange
yellow
green
cyan
blue
violet

Question 10

diffraction of white light

Answer 10

when shone through all different wavelength diffract by different amounts - unclear spectra of colours

Question 11

central maximum

Answer 11

brightest part of pattern as intensity of light is highest in the centre

Question 12

intensity

Answer 12

power per unit area

for monochromatic light, all photons have same energy so increased intensity increases number of photons per second
so more photons per unit area hitting central maximum than other bright fringes

Question 13

width of central maximum

Answer 13

-slit width decreases amount of diffraction means central maximum id narrower but intensity is higher
-if wavelength increases, amount of diffraction increases, CM is wider so intensity lowers

Question 14

two source interference

Answer 14

when waves from two sources interfere to produce a pattern
but be mono and coherent to get a clear pattern

Question 15

maxima

Answer 15

at any two points an equal distance from two sources in phase you will get constructive interference

Question 16

minima

Answer 16

any point where path difference is y/2, 3y/2 etc.
waves arrive out of phase total destructive interfernce

Question 17

double slit

Answer 17

use two coherent light sources or shine a laser through two slits
slits same size as wavelength of light, this makes light from slits act like two coherent point sources

Question 18

if you used white light for double slit

Answer 18

would be less intense with wider maxima made up of different colours with central white fringe

Question 19

double slit equation

Answer 19

w = yD/s

Question 20

diffraction grating

Answer 20

contains lots of equally spaced slits close together
when monochromatic light is passed through a DG with hundreds of slits per mm at normal incidence(right angles to grating)
interference pattern is really sharp

Question 21

zero order line

Answer 21

all maxima in diffraction pattern are sharp lines
line of max brightness at centre is the zero order line
same direction as beam on grating

Question 22

conclusions of diffraction grating

Answer 22

-larger wavelength, more the pattern will spread out
-id d is smaller (grating is coarser), pattern will spread out less
-if for order sintheta < 1 then order doesnt exist

Question 23

optically dense

Answer 23

the more optically dense the more light slows down
measured by refractive index

Question 24

absolute refractive index

Answer 24

ratio between speed of light in a vacuum and speed of light in that material

n = c/cs

Question 25

relative refractive index

Answer 25

ratio of speed of light in material 1 to speed of light in material 2 1n2 = c1/c2 1n2 = n2 / n1 1n2 == 1 going to 2

Question 26

angle of incidence

Answer 26

angle that incoming light makes to the normal

Question 27

angle of reflection

Answer 27

angle reflection ray makes with normal

Question 28

snells law

Answer 28

n1 sin01 = n2 sin02

Question 29

direction and optically density

Answer 29

as light change direction in a medium to a different optically dense material -towards normal is it moves from less optically dense to more -moves away from normal if less to more

Question 30

critical angle

Answer 30

angle of incidence at which angle of refraction is 90

Question 31

total internal reflection

Answer 31

at angle of incidence greater than critical angle, refraction cant happen, means light is refracted back into material

Question 32

optical fibre

Answer 32

very thin flexible tube of glass or plastic fibre that carry light signals over long distances and round coners using TIR

Question 33

step- index optical fibre

Answer 33

-high refractive index(optically dense) -core surrounded by cladding with lower refractive index(less optically dense) to allow TIR -cladding protects fibre from scratches qhich could allow light to escape

Question 34

optical fibre, light travel

Answer 34

light is shone at one end of fibre, fibre is so narrow that light hits boundary between fibre and cladding at angle > 0c so its TIR from boundary tio boundary until it reaches the end

Question 35

optical fibre uses

Answer 35

used to transmit phone and cable TV signals

Question 36

optical fibre advantages

Answer 36

-light carries more info as light has increased frequency -light doesnt heat up fibre to no energy is lost as heat -no electrical interference -cheaper -travel along very quickly with minimal signal loss (some)

Question 37

signal degradation

Answer 37

signal can be degraded by absorbtion or dispersion info can be lost

Question 38

signal absorbtion

Answer 38

where some of signals energy uis absorbed by material fribre its made from results in reduces amplitude of signal reduced

Question 39

signal dispersion

Answer 39

modal/material - pulse broadening where signal received is broader than initial signal broadened pulses can overlap each other and lead to info loss

Question 40

modal dispersion

Answer 40

caused by light rays entering optical fibres at different angles, causing them to take different paths down fibre light travelling straight down get there faster then reflection rays

Question 41

how to prevent modal dispersion

Answer 41

single-mode fibre in which light is only allowed to follow a very narrow path

Question 42

material dispersion

Answer 42

caused by different amounts of refraction experienced by different wavelengths of light different wavelengths slow down by different amounts when entering a different medium as light consists of many different wavelengths, causes parts of signal to take longer time to travel down fibre

Question 43

how to stop material dispersion

Answer 43

use monochromatic light

Question 44

optical fibre repeaters

Answer 44

used to regenerate the signal every so often to help reduce signal degradation(both absorption and dispersion)