2.  Sound Waves
 Light Waves
 Radio Waves
 Water Waves
 Waves on a String

3. But what
is a
WAVE ??

9. A sound wave traveling in one medium
may be partly reflected, refracted or absorb
when it strikes another medium. Sound also
exhibits the properties of
diffraction, interference and the Doppler
effect.

10. The waves bounce back when a train of
waves encounters a barrier. They are said to
be reflected.
Sound waves may be reflected from
walls, mountains, the ground and other
objects. The direction of reflected sounds
may be accurately predicted using the basic
law of reflection. The angle of incidence =
the angle of reflection

12.  Angle of Incidence – angle between the
incident wave and the normal to the
reflecting surface.
 Angle of Reflection – angle between the
reflected waves and the normal. We call the
reflection of sound “echo”.
› Echo is the sound used by SONAR or Sound
Navigation Ranging in detecting and locating
object. SONAR devices emits sound and
measure the time required for the echo to return.
SONAR is used to determine the depth of water.

13. Refraction occurs whenever sound
passes from one medium into
another, where it changes its velocity.
During daytime when the air need the
ground is warmer than the air above, sound
is refracted from the ground, while at
night, the reverse happens. That is why we
hear better at night than during the day.

15. The ability of waves to travel around the
corners or obstacles in their path is what we
called as diffraction. It can be easily
observed because the wave width of the
opening, or size of the obstacle, is nearly the
same order as the wavelength of sound.

17.  Constructive interference – two pulses
moving in opposite direction along a
stretched string are unaffected by their
crossing.
 Destructive interference – complete
cancellation occurs when identical pulses
with opposite displacement by the edges of
the barrier.

19. The Doppler effect is the apparent change
in the frequency of sound due to the motion
of source of sound and/or the observer.

20. Sound may be described by four perceptual
characteristics:
 Pitch – refers to the highness or lowness of a
sound. It depends upon the frequency of the
sounding object. Higher frequency sounds produce
high pitch while lower frequency sounds produce
low pitch.
 Loudness – is a physiological sensation that varies
from one person to another. It depends on the
sense of hearing, the distance from the source and
the material through which the sound travels.

21.  Intensity – depends on the amplitude of
pressure variations within the sound waves.
The unit for this is decibel(dB), named after
Alexander Graham Bell.
 Quality – property of a tone that distinguishes it
from another tone of the same pitch and
intensity produced by a different instrument. It
enables you to identify the source of sound
because tones differ from one another.

22. The ear is our organ of hearing. It is divided
into three parts: outer, middle and inner.

23.  The outer ear is shaped like a funnel and is
called the pinna or auricle. It is that part of our
ear that we have at the side of our head.
 The middle ear is an air-filled space containing
the eardrum or tympanic membrane, the
Eustachian tube and the bridge of auricles. The
eardrum separates the outer ear from the
middle ear.
 The inner ear contains a coiled fluid-filled tube
called the cochlea.

24. The pinna collects the sound waves and
transmits them to the auditory canal. The auditory
canal acts like a closed-tube amplifier producing a
resonant frequency with a wave length equal to four
times its length. The sound waves push on the
eardrum. The pressure variation resulting from the
compression and rare fractions in sound waves
causes the eardrum to vibrate. These vibrations are
transmitted to the liquid in the inner ear. These
vibrations are then received by the nerves and
converted to electrical nerve impulses, the ones
sent to the brain. In the brain, these nerve impulses
are analyzed and interpreted .