waves and photons

Question 1

what are progressive waves?

Answer 1

an oscillation of particles in a medium which transfers energy from one point to another without transferring any material

Question 2

in phase

Answer 2

phase difference = 0

Question 3

in antiphase

Answer 3

phase difference = 180 / pi rad / 1/2lamda

Question 4

out of phase

Answer 4

phase difference does not = 0

Question 5

phase difference in radians

Answer 5

2pi delta t/T or d/lambda 2pi

Question 6

90

Answer 6

pi/2

Question 7

180

Answer 7

pi

Question 8

270

Answer 8

3pi/2

Question 9

360

Answer 9

2pi

Question 10

transverse waves

Answer 10

direction of oscillation of particles is perpendicular to the direction of energy propagation

Question 11

longitudinal waves

Answer 11

direction of oscillation of particles is parallel to the direction of energy propagation

Question 12

polarisation

Answer 12

waves in polarised light only oscillate in one direction
ONLY OCCURS IN TRANSVERSE WAVES

Question 13

application of polarisation

Answer 13

• sunglasses
• TV aerials
  as evidence for nature of transverse waves

Question 14

properties affected by refraction

Answer 14

speed and wavelength vary
frequency is constant

Question 15

refractive index of air

Answer 15

1

Question 16

conditions for total internal reflection

Answer 16

angle of incidence greater than a critical angle

Question 17

optic fibres

Answer 17

thin pieces of glass that carry signal made up of impulses of light
light undergoes TIR when it meets a boundary so no light escapes
cladding has a lower refractive index than core so TIR occurs
cladding protects fibre from scratching

Question 18

modal dispersion

Answer 18

light rays enter at different angles so some take longer to reach end

Question 19

material dispersion

Answer 19

different wavelengths travels at different speeds so arrive at different times (to fix use monochromatic light)

Question 20

diffraction

Answer 20

wave passes through gap of similar size and spreads out

Question 21

single slit diffraction
monochromatic light

Answer 21

bright central fringe/ maximum
alternating bright and dark fringes that get dimmer and narrower than central maximum

Question 22

single slit diffraction
white light

Answer 22

white central fringe/ maximum
other maxima are composed of spectrum
(violet closest to centre and red furthest away)

Question 23

factors affection central maximum

Answer 23

increase wavelength - width of central max increases
increase slit width - width of central max decreases (intensity increases)

Question 24

coherence

Answer 24

constant phase differences
same frequency

Question 25

path difference

Answer 25

difference between distances of 2 waves

Question 26

constructive interference

Answer 26

2 waves in phase reinforce each other produces a wave of greater amplitude path difference = n lambda

Question 27

destructive interference

Answer 27

2 waves are in antiphase cancel out 0 amplitude path difference = (n+1/2) lambda

Question 28

youngs double slit experiment

Answer 28

fire laser beam through single slit causing it to diffract and hit double slits (single slit ensures coherence) light diffracts through both this light superposes to create interference pattern

Question 29

youngs double slit experiment white light

Answer 29

central fringe will be white other fringes will show spectrum of colours with violet closest and red furthest

Question 30

diffraction gratings

Answer 30

fire laser through diffraction grating zero order passes straight through higher order diffracted by an angle

Question 31

diffraction gratings white lights

Answer 31

central beam will be white other will show spectrum of colours with violet closest and red furthest

Question 32

diffraction gratings derivation of formula

Answer 32

Pythagoras theorem sin0 = O/H = n lambda/d

Question 33

stationary waves

Answer 33

energy not transferred along axis of wave amplitude varies along length of wave all particles between 2 adjacent nodes in phase

Question 34

node

Answer 34

0 amplitude

Question 35

antinode

Answer 35

maximum amplitude

Question 36

length of harmonic

Answer 36

1/2 n lambda

Question 37

how are stationary waves formed?

Answer 37

by superposition of 2 progressive waves with same frequency traveling in opposite directions

Question 38

investigation frequency of harmonics

Answer 38

1. find first harmonic (vary oscillator) 2. record frequency 3. record frequency to produce first harmonic when varying - length of string - tension - mass per unit length

Question 39

photoelectric effect (in terms of frequency and energy)

Answer 39

photon energy greater than work function frequency of light greater than threshold frequency

Question 40

factors affecting photoelectric transmission

Answer 40

light intensity photon energy/frequency

Question 41

threshold frequency

Answer 41

minimum frequency requires to remove an electron form the surface of a metal

Question 41

work function

Answer 41

minimum energy requires to remove an electron form the surface of a metal

Question 42

stopping potential

Answer 42

minimum voltage required to stop the fastest moving electrons emitted from a metal

Question 43

photocells

Answer 43

current only flows when photon energy exceeds the work function increasing intensity of radiation increases current

Question 44

how are electrons arranged?

Answer 44

in discrete energy levels

Question 45

excitation

Answer 45

movement of an electron to a higher energy level energy can come from heat or photon collision with another electrons

Question 46

excited atom

Answer 46

atom which is higher than ground state

Question 47

de-excitation

Answer 47

movement to a lower energy level photon release with energy equal to difference between energy levels

Question 48

ionisation

Answer 48

removal of electrons from atom

Question 49

ionisation energy

Answer 49

energy required to remove an electron an electron from an atom

Question 50

fluorescent tubes

Answer 50

- glass tube coated with phosphorus and filled with mercury vapour - high voltage applied across the mercury vapour causing free electrons to collide with electrons in mercury vapour - transfers energy to the mercury electrons exciting the mercury atom to a higher energy levels - electrons in excited mercury atoms relax to lower energy levels emitting UV photons with equal to the difference between energy levels - UV photons are absorbed by phosphorus coating exciting in phosphorus - phosphorus electrons relax by cascading down energy levels emitting lower energy photons in the visible spectrum

Question 51

observing line spectra

Answer 51

light is passed through a diffraction grating causing it to split into its individual wavelengths

Question 52

emission spectra

Answer 52

observed for light emitted by an excited gas colour4edc lines are caused by photons that are emitted when atoms in the gas relax

Question 53

absorption spectra

Answer 53

observed for white light which has passed through a cool gas black lines are caused by photons beings absorbed when they excite atoms in the gas

Question 54

wave - particle duality

Answer 54

waves exhibit particle properties particles exhibit waves properties

Question 55

evidence electron diffraction

Answer 55

- electrons produce a diffraction pattern when they pass through a crystal - electrons diffract as they pass between the atoms and interfere with each other to produce bright and dark fringes when reach the screens

Question 56

evidence photoelectric effect

Answer 56

- when light liberates an electron in the photoelectric effect it gives all of its energy to a single electron - light carries energy in fixed packets is a particle property indictaing that lights behaving as a particle