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Physics > unit 2 wave ( progressive wave ) > Flashcards

unit 2 wave ( progressive wave ) Flashcards

1
Q

waves carry ……

A

waves carry energy without carrying matter

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2
Q

progressive wave

stationary / standing wave

A

transfer energy as a result of oscillations / vibrations

the disturbance which does not transfer energy

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3
Q

longitudinal wave

definition

A

vibrations of the particles parallel to the line of motion the wave

making a series of compression and rarefaction

sound wave

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4
Q

transverse wave

definition

A

vibrations of the particles / field ( electromagnetic wave ) perpendicular to the line of motion the wave

electromagnetic wave

ripples on water surface

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5
Q

longitudinal wave

direction of motion of particles
direction of motion of wave

A

direction of motion of particles
-left right

direction of motion of wave
- right

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6
Q

transverse wave

direction of motion of particles
direction of motion of wave

A

direction of motion of particles
- up down

direction of motion of wave
- right

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7
Q

amplitude

A

maximum displacement from the equilibrium position

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8
Q

wavelength

definition for transverse

A

minimum distance between two in phase point

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9
Q

wavefront

A

a line or surface on which the disturbance has the same phase at all point

  • all the points on a wavefront are in phase
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10
Q

ray

A

a line at right angles to the wavefront which shows the direction of travel

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11
Q

frequency

A

number of complete oscillation of particle / field per unit time

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12
Q

displacement vs time graph
of a point in the wave

difference btwn displacement vs distance and displacement vs time

A

notes pg 2

displacement vs distance

  • amplitude: max displacement
  • involves infinity particles
  • freeze

displacement vs time

  • gradient: velocity
  • v = 0 , a = max ( there’s no resultant force ) at max displacement
  • period=T
  • involves one moving particle
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13
Q

definition of speed of the wave

A

rate of distance travel by wavefront

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14
Q

speed of the wave

derivation of expression

A

notes pg 2

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15
Q

sound wave

speed depends on

frequency depends on

wavelength depends on

A

speed depends on temp, wind , type of gas

frequency depends on source

wavelength depends on depends on speed and frequency

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16
Q

water wave

speed depends on

frequency depends on

wavelength depends on

A

speed depends on depth of water

frequency depends on source

wavelength depends on speed and frequency

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17
Q

wave in spring

speed depends on

frequency depends on

wavelength depends on

A

speed depends on formula pg 2

frequency depends on source

wavelength depends on speed and frequency

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18
Q

electromagnetic wave

speed depends on

frequency depends on

wavelength depends on

A

speed depends on medium

  • fastest in vacuum
  • slower in medium with higher refractive index

frequency depends on source

wavelength depends on speed and frequency

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19
Q

if external conditions remain unchanged

frequency increases, wavelength ?

A

decreases

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20
Q

phase difference

A

the phase diff btwn 2 particles along the wave is the fraction of a cycle by which one move behind the other

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21
Q

phase diff btween 2 waves = 0

waves are ?

A

in phase

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22
Q

phase diff btween 2 waves = 180 / pi rad

waves are ?

A

antiphase

exactly out of phase

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23
Q

path diff = wavelength

phase diff is?

A
  • path diff = wavelength
  • after time = one period, T

phase diff = 360 / 2 pi rad

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24
Q

path diff

by proportional method

A

refer pg 3

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25
Q

propagation of wave

displacement vs distance graph
t = t0 
t = t0 + 1/4 T
t = t0 + 1/2 T
t = t0 + 3/4 T
A

refer pg 4

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26
Q

lagging and leading wave

displacement vs distance graph
displacement vs time graph

draw an example

A

refer pg 5

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27
Q

longitudinal wave

compression is the place where

rarefraction is the place where

A

compression is the place where
-pressure is maximum

rarefraction is the place where
-pressure is minimum

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28
Q

wavelength

definition for longitudinal

A

the minimum distance btwn 2 compressions / rarefractions

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29
Q

at compression and rarefractions

  • particle displacement is ?
  • particle oscillates with … speed and….. acceleration?
A

at compression and rarefractions

  1. particle displacement is
    - 0
  2. particle oscillates with
    - maximum speed
    - 0 acceleration
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30
Q

midpoint btwn rarefrction and compression

  • the amplitude is / particle displacement is ?
  • particle oscillates with … speed and….. acceleration?
A
  1. particle displacement is
    - maximum
  2. particle oscillates with
    - 0 speed
    - maximum acceleration
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31
Q

propagation of sound wave

draw graph 
t = t0 
t = t0 + 1/4 T
t = t0 + 1/2 T
t = t0 + 3/4 T
A

refer pg 6

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32
Q

intensity

define

A

the power per unit area perpendicular to the direction of motion the wave ( Wm-2 )

formula pg 7

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33
Q

intensity of wave proportional to

A

amplitude squared

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34
Q

point source

define

A

source that emits uniformly in all direction

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35
Q

point source

intensity formula

A

pg 7

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36
Q

point source

intensity formula

draw graph
obeys law?

A

inverse square law

draw grapg pg 7

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37
Q

intensity

power received in an angle formula

A

pg 8

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38
Q

point source

-

A
  • distance from point source

- amplitude

39
Q

  • fields
A

electromagnetic wave consist of
- electric
- magnetic
fields

which oscillate at right angles to each other and to their direction of travel

40
Q

properties of electromagnetic wave

name first 3

A
  • all same speed in vacuum = speed of light
  • transfer energy / progressive
  • transverse / can be polarised
41
Q

properties of electromagnetic wave

name next 2

A
  • undergo diffraction / interference / superposition

- can be reflected / refraction

42
Q

properties of electromagnetic wave

name last 2

A
  • oscillating electric and magnetic field

- not affected by electric and magnetic field

43
Q

order of magnitude of electromagnetic wave

give the wavelength

A

radio
micro
infra red

visible light

ultraviolet
x ray
gamma ray

44
Q

frequency of wave can be calculated from

A

pg 9

45
Q
  1. polarisation

plane polarisation

A

vibrations of field ( not particle ) are confined to a single plane perpendicular to the direction of propagation of wave

the plane of vibration includes the direction of energy transfer

46
Q
  1. polarisation

plane polarised light

A

vibrations of electric / magnetic field ( not particle ) are confined to a single plane perpendicular to the direction of propagation of wave

the plane of vibration includes the direction of energy transfer

47
Q
  1. polarisation

unpolarised

A

vibrations occcur in a large number of planes perpendicular to the direction of propagation of wave

48
Q
  1. plane polarisation of micro wave use
A

earth metal rod which is earthed with micro wave receiver and voltmeter

49
Q
  1. plane polarisation

why unpolarised source look dimmer when view from one polaroid

A

polaroid block the vibration into one plane

50
Q
  1. plane polarisation

determine whether the light source is polarise

using one polaroid filter

A

unpolarised source

  • dimmer when view the source through polaroid
  • when rotate the polaroid about its axis parallel to the light propagation , no change in intensity

polarised source

  • when rotate the polaroid about its axis perpendicular to the plane of polaroid , intensity decreases
  • 90 intensity lowest
  • intensity increases again after 90
  • maxima and minima are 90 apart
51
Q
  1. plane polarisation

prove light can be polarised

using 2 polaroids

A
  • rotate ine polaroid and observed intensity varies
  • no light when polaroids are at 90
  • maxima and minima are 90 apart
52
Q

polaroid sunglasses can enable fish to be seen in a pond

A
  • the glare of light are reflected off the surface is partially plane polarised
  • filter at 90 to the polarised reflected light, sunglass cut out the reflected light
  • but not light from fish which is unpolarised
53
Q

3 D image

A

pg 13 and 14

54
Q
  1. diffraction
A

spreading out of waves into shadow reagion when they pass through apertures / around obstacles

55
Q
  1. diffraction

wave speed
frequency
wavelength

A

wave speed
frequency
wavelength

remain constant

56
Q
  1. diffraction

what changes

A

shape and direction

57
Q
  1. diffraction

effect is larger if

  • wavelength is
  • gap is
A

diffraction

effect is larger if

  • wavelength is longer
  • gap is smaller
58
Q
  1. diffraction

the smaller the gap
the lesser the energy can passed through

so the gap cannot be too small to get observation

which is the best for size of gap

A

gap = size of wavelength

best diffraction observed

59
Q
  1. diffraction

draw diagram on water wave

  • small gap
  • large gap
A

pg 15

pink notes

60
Q
  1. diffraction

Q: radio station broadcasts both 198 kHz and 94 MHz
In mountainous part reception is better on long wave than short. why?

A
  1. calculate wavelength of each
    198k - 1520
    94M- 3.2
  2. longer wavelength bigger than mountain
  3. gives larger diffraction
  4. wave able to diffract into shadow region
  5. better diffraction more complete coverage
61
Q
  1. diffraction

Q: the roar of a tiger can be heard from far away even though the tiger cannot be seen because there is a hill in the way

explain the effect

A
  1. diffraction
  2. wavelength of sound is bigger than hill
  3. sound wave able to diffract by hill
  4. spread out into shadow region

link this to experiment to investigate diffraction of sound waves pg 16

62
Q
  1. diffraction
    - single slit diffraction pattern

describe the pattern

A

small gap
dark fringes may be observed

features:

  1. central max fade out gradually
  2. the width of the central max is twice of each subsidiary max
  3. pattern symmetry about central max
  4. minima are not equally spaced
  5. subsidiary maxima are much less intense than the central max

graph
pic ( multiple circular rings )
pg 17

63
Q
  1. superposition of waves
    - principle of superposition of waves

states that

A

whenever two waves meet the total displacement at any point is equal to the vector sum of their individual displacement at that point

64
Q
  1. superposition of waves
    - interference

?

A

when the waves meet, resultant displacement is the sum of the individual displacements

65
Q
  1. superposition of waves

conditions for the waves to superpose / interfere

A
  1. same type of wave
  2. same plane of polarisation
  3. 2 waves must meet
66
Q
  1. superposition of waves

path difference?

A

difference in distance travelled by the waves from source to observer

how much further one route is than another

67
Q
  1. superposition of waves

ways to produce path difference

A

change the relative position of the sources to observer

moves one of the sources or moves the observer

68
Q
  1. superposition of waves

path difference changes

A

path difference changes phase difference

69
Q
  1. superposition of waves

phase difference formula

A

pg 18

70
Q
  1. superposition of waves

constructive
destructive
interference

definition

A

constructive interference
- superposition of in phase waves and produces a wave of increased amplitude

destructive interference
- superposition of antiphase waves and produces a wave of reduced or zero amplitude

71
Q
  1. superposition of waves

constructive
destructive
interference

condition in terms of path and phase diff

A

pg 18

72
Q
  1. superposition of waves

conditions that must be satisfied for the intensity of waves at a point to be zero

A
  1. phase diff is pi rad
  2. or path diff is 1/2 lamda
  3. same intensity at point
  4. intensity of first wave / intensity of second wave
    ( formula )
73
Q
  1. superposition of waves

if frequency of the source is allow to change and the path diff remains the same

wavelength to be occur are

A

1/2 lamda = path diff
3/2 lamda = path diff
5/2 lamda = path diff

lamda?
pg 19

74
Q
  1. superposition of waves

as path diff increase, the diff in amplitude ?
what happens next

A

as path diff increase, the diff in amplitude of the 2 waves at detector increases

cancellation becomes incomplete and caused the amplitude of the destructive interference no longer zero

interference pattern becomes blur

75
Q
  1. superposition of waves

coherence

A

coherence :

phase diff btwn 2 sources / waves is constant

76
Q
  1. superposition of waves

methods to produce coherent sources
water wave:
sound wave:
electromagnetic wave:

A

water wave: dippers connected to single motor
sound wave:loudspeakers connected to amplifier
electromagnetic wave: diffraction ( double slit ) or reflection ( partially reflected surface )

77
Q
  1. superposition of waves

conditions for interference

A

coherence for electromagnetic wave / same frequency for water / sound wave

same amplitude at that point of observation

fringes far apart to distinguished

78
Q
  1. superposition of waves

observation / draw the diagram
of interference of water wave
label constructive / destructive interference

A

pg 21

79
Q
  1. superposition of waves

wavefront constant means

A

speed is constant

80
Q
  1. superposition of waves

factors affect the separation btwn adjacent constructive interference

A
  1. separation of sources were increased, separation decreased
  2. wavelength increased, separation increase
  3. depth increase, wavelength would increase and hence separation increased
81
Q
  1. superposition of waves
    - sound waves

noise cancelling headphones
how it works

A

sound waves enter and pass through headphone
detected by microphone
electronic circuit sends a signal to loudspeaker
produces an opposite wave
to cancel the incoming soundwave

82
Q
  1. superposition of waves
    - sound waves

investigate the interference

plan

A

pg 22

83
Q
  1. superposition of waves
    - sound waves

Q: cancelling headphones work well from engine noise but not with speaking voices

why

A

noise of vibrating object has a constant pitch / frequency

speech / sound varies in pitch / amplitude

difficult to match the changing frequency

84
Q
  1. superposition of waves
    - sound waves

conditions to produce complete cancellation

A
  1. waves must have same frequency / wavelength
  2. waves must have same amplitude
  3. waves must 180 degree / pi rad apart / half wavelength / half a cycle apart / antiphase
85
Q
  1. superposition of waves
    - interference of microwaves

why alternate maxima and minima of intensity are observed when detector move from A to B?

A
  1. waves are diffracted from each slit acts as a source
  2. the waves from each source are coherence since derived from a single source
  3. when these waves meet and superpose, a series of maximum and minimum intensity is detected
  4. path diff changes as detector moves around AB
  5. maximum when the waves in phase and path diff= n lamda
  6. minimum when the waves in antiphase and path diff = n+1/2 lamda
86
Q
  1. superposition of waves
    - interference of microwaves

microwave- how to reduced uneven heating

A

place food on rotating turntable

food moves through hot and cold spots

over time period all part of food received similar amount of energy

87
Q
  1. superposition of waves
    - interference of visible light

a thin film of oil can produce interference patterns with monochromatic light ( coloured interference patterns with white light )

explain

A
  1. rays reflected from air-oil and oil-water interface act as coherence sources
  2. the ray reflected from oil-water interference passes through a longer path ( path diff = 2 times thickness of oil )
  3. they superpose when they meet and interference pattern is produced
  4. if they meet in phase , constructive interference and bright fringe is observed
  5. if they meet in antiphase , destructive interference and dark fringe is observed
88
Q
  1. superposition of waves
    - interference of visible light

compact disc

A

pg 25

89
Q
  1. superposition of waves
    - interference of visible light
coherent source by diffraction
thoughts on 
- monochromatic light
- small slit in front of a filament light 
- laser
A

light sources
- monochromatic light : not that coherent

  • small slit in front of a filament light : the diffracted light is coherent with itself at least
  • laser : already monochromatic much more coherent, brighter , no need for single slit to sample light ,easier to demonstrate superposition of light
90
Q
  1. superposition of waves
    - interference of visible light

young’s double slit

draw the overall idea

A

pg 26

91
Q
  1. superposition of waves
    - interference of visible light

the fringes observed

draw and explain

A

pg 26

92
Q
  1. superposition of waves
    - interference of visible light

formula to calculate fringe separation

A

pg 27

only apply to visible light which the angle is very small

93
Q
  1. superposition of waves
    - interference of visible light

explain the pattern of fringes

&number of fringe depends on

A
  1. interference is incomplete ( not exactly cancelled out ) except central max bright fringes
  2. because the amplitudes of the two waves are not exactly equal due to different wave front
  3. intensity of fringes is very low

amount of diffraction occurring at slits which depend son width
narrower slit, larger diffraction , greater number of fringes , fainter due to less light get through

94
Q
  1. superposition of waves
    - interference of visible light

measurement of wave length

formula

A

pg 28

single slit and double slit is used for filament lamp
double slit is used for laser

  • remember X the distance across few fringes to nth from central maximum?
  • use that measured few times and get average value

use formula … derived previously for Xn

!! the formula can only applied to visible light !! NOT MICROWAVE etc

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