AL Physics Revision Notes/ Wave
P.1
B1
Syllabus
Nature of motions in
longitudinal
and
transverse progressive
waves.
Relation between v, 
and f.
Velocity of propagation
of mechanical waves
along stretched strings
or springs and in solids.
Wave Propagation
Notes
Experiments
Questions will not be set on the E5 Investigation of the speed
equation
of
transverse
or
longitudinal progressive
y  a sint  kx  , but an
waves along a slinky
understanding of the variation of
spring.
displacement with time ( x
constant ) and with distance ( t
constant ) in a progressive wave is
expected.
Factors affecting the speed of
propagation.
The
expression
v
T
m
and
E
( proof not required ).

1. Transverse wave VS Longitudinal wave
 If the direction of vibration of particles is perpendicular to that of propagation of the wave,
the wave is called a transverse wave.
 When the direction of vibration is along the direction of the propagation of the wave, then
we called this kind of wave a longitudinal wave.
2. Wave speed of Mechanical waves
a. Mechanical waves along stretched strings or springs
 The velocity of mechanical waves in string or springs is given by
v
T
m
v
E

where T is the tension of the strings or springs
m is the mass per unit length ( linear density )
b. Mechanical waves in solids
 The velocity in mechanical waves in solids is given by
where E is the Young modulus which tell us the degree of elasticity
 is the density of the solids
B2 Wave Phenomena
Syllabus
Wave phenomena
Huygens’ principle
Notes
Familiarity
with
ripple
tank
experiments is assumed from lower
form work.
Explanation of laws of reflection and
refraction.
Experiments
AL Physics Revision Notes/ Wave
Reflection
Refraction
Polarisation
Examples to include brief discussion
of radar, sonar and long distance
propagation of radio waves by
reflection from the ionosphere.
Phase
change
on
reflection,
illustrated for example, using a
slinky spring.
Refraction as a result of change in
wave speeds. Refractive index in
terms of speeds.
Polarisation by selective absorption,
reflection and scattering. Practical
applications to include polaroid
spectacles, VHF and UHF antennas
(briefly).
P.2
E6
Superposition
Mathematical treatment not required.
E7
Beats
Qualitative treatment. Use in tuning.
E8
Diffraction
Diffraction of light at apertures E9
( simple qualitative treatment only ).
Two-source
interference
with E10
quantitative treatment for maxima
and minima.
Conditions
for
observable
interference.
Practical applications of interference E11
to include the blooming of lenses
and the testing of the flatness of a
surface ( very briefly ). Quantitative
treatment of interference effects at E12
normal incidence in parallel-sided
and wedge-shaped thin films.
Everyday examples to include the
colours of oil films and soap
bubbles.
Newton’s
rings
( qualitatively ).
Plane transmission grating as an
interference system. Use of the
formula d sin   n .
Proportionality between intensity
and square of the amplitude ( by
analogy with harmonic oscillator and
energy delivered by an alternating
current ). Energy distribution in
interference patterns.
Interference
Polarisation of light by
a. reflection from a
shiny surface ( e.g.
water,
glass,
bench-top ).
b. absorption ( polaroid
spectacles ).
c. scattering ( blue sky
viewed
through
polaroid ).
Superposition of waves
on a slinky spring.
Observation of beat
waves forms on a CRO.
Looking through holes.
Estimation
of
wavelength of light by
a. double slit, and
b. plane
diffraction
grating.
Observation
of
interference fringes in
soap
films,
and
Newton’s rings.
Wave amplitude and
energy when waves are
superposed.
AL Physics Revision Notes/ Wave
P.3
1. Huygens’ principle
 It states that:
All points on a wavefront can be considered as point sources
for the production of spherical secondary wavelets. After a
time t, the new position of the wavefront will be the surface
tangential to these secondary wavelets.
 Prediction of the propagation of a plane wave by Huygens’ Principle.
 Explaining reflection
 Explaining refraction and derive Snell’s law
sin i 1 n 2


sin i 2 n 1
2. Phase change due to Reflection
a. Reflection at fixed end (from a medium of high speed to a medium of lower speed)
There will be a 180o phase change for the reflected wave.
b. Reflection at free end (from a medium of low speed to a medium of higher speed.)
The reflected wave will be in phase with the incident wave.
3. Application of reflection
a. RADAR
b. SONAR
c. Long distance propagation of radio waves, reflection by the ionosphere.
4. Polarization
a. Polarization by absorption
b. Polarization by reflection
c. Polarization by scattering
d. Polarization by metal grid
e. Checking Polarization
f. Change of amplitude and intensity after polarization
5. Superposition
 The principle of superposition states that
When two pulses travel past a point in a string at the
same time, the displacement of the string at that point is
the sum of the displacement each pulse would produce
there by itself.
6. Beats
a. Production of beats
b. Explanation of the production of beats
c. Beat frequency
d. Uses
1. Tuning of musical instrument
AL Physics Revision Notes/ Wave
P.4
2. Detecting speed of cars.
7. Diffraction
a. Waves bend around the edge of an obstacle in their path, this behaviour is called diffraction.
b. Single slit diffraction pattern : depending the size of slit width relative to the magnitude of
wavelength
8. Interference
 So interference refer to the superposition of wave from a finite number of coherent sources.
a. Conditions for observable interference
1. Coherent sources : The two sources should have the same frequency such that a constant
phase relationship is maintained.
2. Sources have same amplitude
3. Transverse wave must be either unpolarized, or have significant resolved parts in the
same plane
b. Double slits interference
1. Conditions for maxima and minima
i) Maximum at P
d sin   n
ii) Minimum at P
1

d sin    n   

2
n = 0, 1, 2, 3,…
n = 0, 1, 2, 3,…
2. Fringe width
w
D
d
c. Diffraction grating
 Then the principal maximum can be obtained if the path difference equal to the
multiples of wavelength.
d sin   n
n = 0, 1, 2,…
d. Intensity
 Also, the intensity of light decreases as the distance of observation increases.
1
I  2
r
 For the same wavelength and slit separation, all the bright and dark fringes appears at
the same position for the different no. of slits used.
 However, as the number of slits increases, the bright lines become sharper.
e. Interference of thin films
 m


General rules : optical path difference (2nt) + phase change (
or 0) = 
1
2
(m  2 )
1. Blooming of lenses
3. Wedge-shape thin film
2. Parallel-sided thin film
4. Newton’s ring
AL Physics Revision Notes/ Wave
P.5
B3 Electromagnetic Wave
Syllabus
The
electromagnetic
spectrum
Notes
Knowledge of approximate frequency and
wavelength of all members of the spectrum and
their common properties.
Experiments
1. Nature of electromagnetic waves
 All EM waves can propagate through vacuum.
 There are 4 properties of EM waves:
1. The variation of electric and magnetic fields occur simultaneously. That means they
have maxima and minima at the same time and in the same places.
2. The direction of electric and magnetic fields are perpendicular to each other and to the
3.
direction of propagation.
The magnitude of the two fields are proportional to each other, E  cB .
4.
The speed of the waves depends only on the electric and magnetic properties of the
medium they travel in, not on the amplitudes of the field variations.
2. EM wave spectrum
a. Approximate frequencies and wavelengths
radio waves in m
microwaves in cm
Infra Red
about 10-4 m to 10-7 m
Visible light 4×10-7 m to 7×10-7 m
Ultra violet
X-ray
Gamma ray
10-7 m to 10-9 m
10-10 m to 10-12 m
10-11 m to 10-13 m
b. Properties of different types of EM waves
B4 Stationary Wave
Syllabus
Stationary waves.
Modes of vibrations of
strings and air columns.
Harmonics and the quality
of sound.
Notes
Graphical treatment only.
1. Stationary waves
a. Stationary waves along string
b. Air columns
1. Closed end
2. Open end
Fundamental frequency, overtones, harmonics
2. Quality of sound
E13
Experiments
A selection of stationary
wave demonstrations.
AL Physics Revision Notes/ Wave
a. Loudness
P.6
b. Pitch
c. Quality
B5 Acoustics
Syllabus
Notes
Experiments
Acoustics.
Pressure and displacement in sound waves.
Intensity
and Frequency response of the ear. Relationship
loudness.
between intensity and loudness. Thresholds
The decibel.
of hearing and pain. Noise pollution (very
briefly). Typical noise levels in everyday
life. Absorption of sound and sound
proofing.
Velocity of sound. Order of magnitude of speed of sound in E14 Measurement of the speed of
solids, liquids and gases. Knowledge of
sound by Kundt’s tube.
1/ 2
( P /  )
not required.
Doppler effect
Quantitative treatment ( change in the
observed frequency and wavelength ) for a
stationary medium and movement along
the source-observer line. Real life
examples ( police cars, ambulances and
radar speed traps, galaxy red shift
indicating expanding universe, all treated
qualitatively ).
1. Pressure and displacement in sound wave
a. Displacement variation
b. Pressure variation
2. Sound intensity
a. Intensity
I 
P
4r 2
3. Sound Intensity Level
  10 log
I
Io
a. Absorption of sound and sound proofing
4. Speed of sound
v g v l v s
a. Measurement of speed of sound by Kundt’s tube
5. Doppler effect
a. Moving observer with moving observer
b. Moving source with moving source : change of wavelength as wave crowded together or
spaced out (For change in wavelength, only consider the motion of the source)
c. In general, both observer and source are moving
v  uo
f f
v  us
the upper sign for motion towards each other
other
the lower sign for motion away from each
AL Physics Revision Notes/ Wave
P.7
d. Application
1) Siren
2) Detecting the speed of vehicles
 Speed of image source = 2 × speed of vehicle
3) Red shift
 This can be use to support the theory of expanding universe.
B6 Optical Instrument
Syllabus
Optical instruments
Notes
Qualitative understanding of
how optical instruments work
( using simple ray diagrams
only ).
Magnifying glass
Magnifying
powers
of
magnifying glass, microscope
and
refracting
telescope
considered as ratio of visual
angles subtended by the image
and the object ( as obtained
from simple ray diagram ).
Two-lens type only. Formation
of image at least distance of
distinct vision.
Two-lens type only. Formation
of image at infinity.
Qualitative explanation of the
functions of the collimator and
the
telescope
using
ray
diagrams. Use in simple
spectral analysis.
Microscope
Refracting telescope
Grating spectrometer
1. Magnifying Power
a. Visual Angle subtended by object

h
D
b. Visual angle subtended by image
c. Magnifying Power
visual angle subtended by the image 
M 

visual angle subtended by the object 
2. Magnifying glass
Experiments
For the purpose of the
practical
examination
familiarity with use of
concave
and
convex
mirror, converging and
diverging lenses, and
prisms is expected but full
instruction on procedure
will be given and
knowledge of particular
methods is not required.
AL Physics Revision Notes/ Wave
P.8


M
h
D
h
D
 h'

 h
 In general,
D
D
M 
f
uo
3.) Microscope
 The microscope is said to be in normal adjustment when the final image I2 is at the near
point of the observer.
 Then,

h
D

h2
D
h2
h
h
h
M  2 1
h1 h
M  me  mo
M 

4. Refracting telescope
 In this case, the refracting telescope is said to be at normal adjustment where the focus of
the two lens overlap with each other.
 So the final image will be formed at infinity.
 Then,


h1
fo
h1
fe
M 
fo
fe
5. Grating Spectrometer


 2  1
2
d sin 
n
 Overlapping of 2nd maximum with the 3rd maximum.