unit 2 wave ( progressive wave ) Flashcards
(94 cards)
1
Q
waves carry ……
A
waves carry energy without carrying matter
2
Q
progressive wave
stationary / standing wave
A
transfer energy as a result of oscillations / vibrations
the disturbance which does not transfer energy
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
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
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
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
7
Q
amplitude
A
maximum displacement from the equilibrium position
8
Q
wavelength
definition for transverse
A
minimum distance between two in phase point
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
10
Q
ray
A
a line at right angles to the wavefront which shows the direction of travel
11
Q
frequency
A
number of complete oscillation of particle / field per unit time
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
13
Q
definition of speed of the wave
A
rate of distance travel by wavefront
14
Q
speed of the wave
derivation of expression
A
notes pg 2
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
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
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
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
19
Q
if external conditions remain unchanged
frequency increases, wavelength ?
A
decreases
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
21
Q
phase diff btween 2 waves = 0
waves are ?
A
in phase
22
Q
phase diff btween 2 waves = 180 / pi rad
waves are ?
A
antiphase
exactly out of phase
23
Q
path diff = wavelength
phase diff is?
A
- path diff = wavelength
- after time = one period, T
phase diff = 360 / 2 pi rad
24
Q
path diff
by proportional method
A
refer pg 3
25
propagation of wave
```
displacement vs distance graph
t = t0
t = t0 + 1/4 T
t = t0 + 1/2 T
t = t0 + 3/4 T
```
refer pg 4
26
lagging and leading wave
displacement vs distance graph
displacement vs time graph
draw an example
refer pg 5
27
longitudinal wave
compression is the place where
rarefraction is the place where
compression is the place where
-pressure is maximum
rarefraction is the place where
-pressure is minimum
28
wavelength
definition for longitudinal
the minimum distance btwn 2 compressions / rarefractions
29
at compression and rarefractions
- particle displacement is ?
- particle oscillates with ... speed and..... acceleration?
at compression and rarefractions
1. particle displacement is
- 0
2. particle oscillates with
- maximum speed
- 0 acceleration
30
midpoint btwn rarefrction and compression
- the amplitude is / particle displacement is ?
- particle oscillates with ... speed and..... acceleration?
1. particle displacement is
- maximum
2. particle oscillates with
- 0 speed
- maximum acceleration
31
propagation of sound wave
```
draw graph
t = t0
t = t0 + 1/4 T
t = t0 + 1/2 T
t = t0 + 3/4 T
```
refer pg 6
32
intensity
define
the power per unit area perpendicular to the direction of motion the wave ( Wm-2 )
formula pg 7
33
intensity of wave proportional to
amplitude squared
34
point source
| define
source that emits uniformly in all direction
35
point source
intensity formula
pg 7
36
point source
intensity formula
draw graph
obeys law?
inverse square law
draw grapg pg 7
37
intensity
power received in an angle formula
pg 8
38
point source
intensity depends on
-
-
- distance from point source
| - amplitude
39
electromagnetic wave consist of
-
-
fields
electromagnetic wave consist of
- electric
- magnetic
fields
which oscillate at right angles to each other and to their direction of travel
40
properties of electromagnetic wave
name first 3
- all same speed in vacuum = speed of light
- transfer energy / progressive
- transverse / can be polarised
41
properties of electromagnetic wave
name next 2
- undergo diffraction / interference / superposition
| - can be reflected / refraction
42
properties of electromagnetic wave
name last 2
- oscillating electric and magnetic field
| - not affected by electric and magnetic field
43
order of magnitude of electromagnetic wave
give the wavelength
radio
micro
infra red
visible light
ultraviolet
x ray
gamma ray
44
frequency of wave can be calculated from
pg 9
45
1. polarisation
plane polarisation
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
1. polarisation
plane polarised light
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
1. polarisation
unpolarised
vibrations occcur in a large number of planes perpendicular to the direction of propagation of wave
48
1. plane polarisation of micro wave use
earth metal rod which is earthed with micro wave receiver and voltmeter
49
1. plane polarisation
why unpolarised source look dimmer when view from one polaroid
polaroid block the vibration into one plane
50
1. plane polarisation
determine whether the light source is polarise
using one polaroid filter
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
1. plane polarisation
prove light can be polarised
using 2 polaroids
- rotate ine polaroid and observed intensity varies
- no light when polaroids are at 90
- maxima and minima are 90 apart
52
polaroid sunglasses can enable fish to be seen in a pond
- 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
3 D image
pg 13 and 14
54
2. diffraction
spreading out of waves into shadow reagion when they pass through apertures / around obstacles
55
2. diffraction
wave speed
frequency
wavelength
wave speed
frequency
wavelength
remain constant
56
2. diffraction
what changes
shape and direction
57
2. diffraction
effect is larger if
- wavelength is
- gap is
diffraction
effect is larger if
- wavelength is longer
- gap is smaller
58
2. 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
gap = size of wavelength
best diffraction observed
59
2. diffraction
draw diagram on water wave
- small gap
- large gap
pg 15
| pink notes
60
2. diffraction
Q: radio station broadcasts both 198 kHz and 94 MHz
In mountainous part reception is better on long wave than short. why?
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
2. 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
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
2. diffraction
- single slit diffraction pattern
describe the pattern
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
3. superposition of waves
- principle of superposition of waves
states that
whenever two waves meet the total displacement at any point is equal to the vector sum of their individual displacement at that point
64
3. superposition of waves
- interference
?
when the waves meet, resultant displacement is the sum of the individual displacements
65
3. superposition of waves
conditions for the waves to superpose / interfere
1. same type of wave
2. same plane of polarisation
3. 2 waves must meet
66
3. superposition of waves
path difference?
difference in distance travelled by the waves from source to observer
how much further one route is than another
67
3. superposition of waves
ways to produce path difference
change the relative position of the sources to observer
moves one of the sources or moves the observer
68
3. superposition of waves
path difference changes
path difference changes phase difference
69
3. superposition of waves
phase difference formula
pg 18
70
3. superposition of waves
constructive
destructive
interference
definition
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
3. superposition of waves
constructive
destructive
interference
condition in terms of path and phase diff
pg 18
72
3. superposition of waves
conditions that must be satisfied for the intensity of waves at a point to be zero
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
3. superposition of waves
if frequency of the source is allow to change and the path diff remains the same
wavelength to be occur are
1/2 lamda = path diff
3/2 lamda = path diff
5/2 lamda = path diff
lamda?
pg 19
74
3. superposition of waves
as path diff increase, the diff in amplitude ?
what happens next
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
3. superposition of waves
coherence
coherence :
phase diff btwn 2 sources / waves is constant
76
3. superposition of waves
methods to produce coherent sources
water wave:
sound wave:
electromagnetic wave:
water wave: dippers connected to single motor
sound wave:loudspeakers connected to amplifier
electromagnetic wave: diffraction ( double slit ) or reflection ( partially reflected surface )
77
3. superposition of waves
conditions for interference
coherence for electromagnetic wave / same frequency for water / sound wave
same amplitude at that point of observation
fringes far apart to distinguished
78
3. superposition of waves
observation / draw the diagram
of interference of water wave
label constructive / destructive interference
pg 21
79
3. superposition of waves
wavefront constant means
speed is constant
80
3. superposition of waves
factors affect the separation btwn adjacent constructive interference
1. separation of sources were increased, separation decreased
2. wavelength increased, separation increase
3. depth increase, wavelength would increase and hence separation increased
81
3. superposition of waves
- sound waves
noise cancelling headphones
how it works
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
3. superposition of waves
- sound waves
investigate the interference
plan
pg 22
83
3. superposition of waves
- sound waves
Q: cancelling headphones work well from engine noise but not with speaking voices
why
noise of vibrating object has a constant pitch / frequency
speech / sound varies in pitch / amplitude
difficult to match the changing frequency
84
3. superposition of waves
- sound waves
conditions to produce complete cancellation
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
3. superposition of waves
- interference of microwaves
why alternate maxima and minima of intensity are observed when detector move from A to B?
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
3. superposition of waves
- interference of microwaves
microwave- how to reduced uneven heating
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
3. 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
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
3. superposition of waves
- interference of visible light
compact disc
pg 25
89
3. superposition of waves
- interference of visible light
```
coherent source by diffraction
thoughts on
- monochromatic light
- small slit in front of a filament light
- laser
```
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
3. superposition of waves
- interference of visible light
young's double slit
draw the overall idea
pg 26
91
3. superposition of waves
- interference of visible light
the fringes observed
draw and explain
pg 26
92
3. superposition of waves
- interference of visible light
formula to calculate fringe separation
pg 27
only apply to visible light which the angle is very small
93
3. superposition of waves
- interference of visible light
explain the pattern of fringes
&number of fringe depends on
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
3. superposition of waves
- interference of visible light
measurement of wave length
formula
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
