Reflection of Waves  
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Is the abrupt change in the direction of propagation of a wave that strikes the  
boundary between two different medium.  
See the figure below  
Reflection of Mechanical Waves  
Laws of reflection of waves  
1st.”The angle of incidence is equal to the angle of reflection  
”
2nd. “The incident direction of propagation, the reflected direction of propagation and  
the normal all lie in the same plane  
”
Applications of Reflection of Waves  
Is used in the designing of plane mirrors  
Reflection of waves(sound waves) used in measuring distances  
Sonar system rely on the reflection of sound waves to assist ships in  
navigating, communicating and detecting other vessels  
In geology, it is important in the study of seismic waves  
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N.B  
SONAR = Sound Navigation and Ranging  
Ripple Tank Experiment  
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R
ipple tank Is a shallow glass tank of water used in schools and colleges to  
demonstrate the basic properties of waves.  
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It is useful in demonstrating wave properties such as reflection and refraction  
.
Main Parts of Ripple Tank  
(a) Shallow tank of water  
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Shallow tank of water is the source of waves in which an oscillating paddle  
generates parallel water waves  
(b) Motor  
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The rotating armature (axle) of an electric motor makes the wooden (metal bar) to  
vibrate on water surface and generating ripples  
(c) Oscillating paddle  
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Oscillating paddle is the one in which transform mechanical energy generated by  
motor by off centre mass to wave energy in a Shallow tank of water  
(d) Lamp (Bulb/ filament)  
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Bulb or filament which is used to illuminate the water surface to see the water waves  
onto the white board or white sheet below the ripple tank  
(e) Paper sheet  
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Paper sheet used to display shadow of the wave pattern placed under the tank  
(f) Various obstacles  
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Various obstacles is paced in the tray to observe properties of waves e.g. reflection,  
refraction, interference and diffraction. Example, laying glass rectangular barrier,  
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curved barrier (concave and convex barrier) etc  
(g) Stroboscope  
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The stroboscope enables the observer to see the waves as stationary  
(h) Laying glass  
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Laying glass used to vary the depth (tray thickness) of the water. This allows  
observing waves travelling from one to another medium  
(i) Metal bar  
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A metal bar (wooden bar) is screwed to the electric motor and suspended above the  
ripple tank with rubber (elastic) bands and touching the water surface  
(j) Power supply  
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Power supply for electric motor  
Refraction of Waves  
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Is the change in direction of waves as they pass from one media to another  
due to change in speed and wave length  
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It obeys Snell’s law: ie  
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The speed of waves depends on the medium i.e velocity of the waves  
decrease with decrease in wavelength. 풗 ∝ 흀  
풗
풗
ퟏ
풗
ퟏ
흀
ퟏ
That is: 풗 = 풌흀 →  
=
→
=
흀
흀
ퟏ
풗
ퟐ
흀
ퟐ
풗
ퟏ
But the ratio  
,
is the refractive index of the second medium  
풗
ퟐ
relative to the first medium  
N.B  
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The length of water waves in shallow water is usually shorter than in deep water  
When wave is refracted into a less medium, the speed of wave increases and vice versa  
When wave is refracted into a less medium, the wave length of wave  
increases and vice versa  
Applications of Refraction of Waves  
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It is used in optical instruments which focus or spread light. For Example,  
microscopes and telescopes  
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It is used in dispersion of light waves  
It is used to determine the eye’s refractive error  
Individual task  
1. During the day sound from distant sources are not very clear unlike during the night  
ANS  
:
During the day sound waves are refracted upwards from the hot earth, while  
at night, sound waves are refracted downwards, hence are much louder.  
2. Give reason why the amplitude of the wave does not change as it crosses the  
boundary  
ANS: Because there is no LOSS of energy therefore amplitude does not change  
Interference of Waves  
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Is a phenomenon in which two waves superpose to form a resultant wave of  
greater, lower, or the same amplitude  
OR  
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Is the pattern formed when two or more waves overlap in medium  
Types of Interference  
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Constructive Interference  
Destructive Interference  
Principle of Superposition  
It states that  
“
The resultant displacement at any points is equal to the sum of the  
displacements of different waves at the point  
”
NB:  
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When two different crests meet at the same point in the same direction results  
a greater amplitude than individual, this refers as constructive interference  
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When crest and trough meet at the same point in the opposite direction results  
smaller amplitude than individual, this refers as destructive interference  
N.B  
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Soft sound occurs in regions where sound waves interfere destructively  
Loud sound occurs where sound waves interfere constructively  
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Node: Is a point on a stationary wave where particles have zero displacement  
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Antinode  
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Is a point on a stationary wave where particles have maximum displacement  
Applications of Interference of wave  
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Creation of hologram. holograph is a photograph of an interference pattern  
which is able to produce a three dimensional image when suitably illuminated  
Noise reduction system. For example, earphones capture environment sound  
which destructed by second computer sound  
Concert halls and auditoriums designed to reduce the amount of destructive  
interference by introducing sound absorber  
Diffraction of Waves  
Diffraction: Is the change in the direction of waves as they pass through an opening  
or around a barrier in their pass  
OR  
Is the spreading of waves around obstacles  
NB:  
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It is possible to hear sound round obstacles but not possible to see light. This is because  
sound waves have longer wavelengths therefore are more readily diffracted unlike  
light waves , which have very short wavelengths therefore not readily diffracted  
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Diffraction of wave is greater when the wave length and width of the gap is the same  
We hear someone sound even she/he behind the building due to diffraction of wave sound