Transcript Sound Waves & Electromagneic W

By: Akina Stafford
Form: 5E
Sound Waves
 Sound waves are longitudinal waves. The particles
carrying the sound vibrate about fixed positions
parallel to the direction in which the sound travels.
Production and Propagation
 Sound waves travel through solids, liquids and
gases, i.e. through any medium which contains
atoms or molecules.
 Sound waves are always generated when an
object or medium vibrates. Examples of objects
that generate familiar sounds are a drum
membrane, a guitar string and our vocal cords.
The vibrating object then transmits the
vibrations to the surrounding medium and in
this way the wave has been generated and starts
to propagate.
Example: Drum
Membrane
The diagram above
shows a drum with its
vibrating membrane
generating
compressions and
expansions
(rarefactions) in air and
therefore, generating
sound waves.
How sound is Transmitted
 Because sound is transmitted as a compression wave, it
can travel only through a medium that contains
particles that can be forced closer together or further
apart. Sound cannot be transmitted in a vacuum
because there are no particles to push closer together
or spread out.
Example:
A ringing bell is placed
in a jar and air inside
the jar is evacuated.
Once air is removed
from the jar, the sound
of the ringing bell is no
longer heard. The
clapper is seen striking
the bell; but the sound
which it produces
cannot be heard
because there are no
particles inside of the
jar to transport the
disturbance through
the vacuum.
Wave Parameters
 The success of any operation conducted in the ocean
environment may depend on the height of the seas,
the direction of the seas and the wave period. Waves,
in general, are described by wave height, wave length,
and wave period. Wave direction is another important
aspect used to describe waves.
Pitch
 Pitch = Frequency of Sound
 The perceived pitch of a sound is just the ear’s
response to frequency, i.e., for most practical purposes
the pitch is just the frequency. Rapidly vibrating
objects produce sounds of high frequency or pitch.
Slowly vibrating objects produce sounds of low
frequency or pitch.
Example:
 The Violin
 The sound from a
violin is of higher pitch
than that from a
double bass because
the sound from the
violin makes the
eardrum vibrate at a
faster rate. Sounds
from the violin have
higher frequencies.
Loudness
 Sound loudness is a subjected term describing the
strength of the ear’s perception of a sound. The
loudness of a sound depends on: the amplitude of the
vibrator producing it- the greater the amplitude of the
vibration, the louder the sound and the ‘amount of
energy’ reaching our ears.
Speed of Sound
 The speed at which sound propagates (or travels from
its source) is directly influenced by both the medium
through which it travels and the factors affecting the
medium, such as altitude, humidity and temperature
for gases like air. To estimate the speed of sound the
principle method is used: speed =
distance sound travels
time taken
Speed of sound of some materials
Medium:
Air (dry)
Water
Iron
Concrete
Carbon dioxide
Speed of sound at
0ºC/ms-1:
330
1400
2700
5000
265
Example:
 Thunder is the sound
_-
made by lightning. The
sudden increase of
pressure and temperature
by the lightning produces
rapid expansion of the air
surrounding and within a
_
bolt of lightning. In turn,
this expansion of air
creates a sonic shock wave
which produces the sound
of thunder.
Audio Frequencies
Sensitivity of the Human Ear:
 The human ear can respond to minute pressure
variations in the air if they are in the audible
frequency range, roughly 20 Hz (Hertz) – 20 kHz
(Kilo- Hertz). Contributing to the wide dynamic
range of human hearing are protective
mechanisms that reduce the ear’s response to very
loud sounds.
Example :
Reflection of Sound Waves
 When Sound waves from a point source strike a plane
wall, they produce reflected spherical wave-fronts as if
there were an ‘image’ of the sound source at the same
distance on the other side of the wall.
Refraction of Sound Waves
 Refraction is the bending of waves when they enter a
medium where their speed is different. Refraction is
not so an important phenomenon with sound as it is
with light where it is responsible for image formation
by lenses, the eye, cameras, etc. But bending of sound
waves does occur and is an interesting phenomena in
sound.
Refraction of Sound
If the air above the earth is warmer than that at the surface, sound will be
bent back downward toward the surface by refraction.
Diffraction of Sound Waves
 Diffraction is the bending of waves around small
obstacles and the spreading out of waves beyond small
openings.
 * small in this case is compared to wavelength.
Electromagnetic Waves
 Electromagnetic waves are
formed when an electric
field (shown as blue
arrows) couples with a
magnetic field (shown as
red arrows). The electric
and magnetic fields of an
electromagnetic wave are
perpendicular to each
other and to the direction
of the wave.
Properties of Electromagnetic Waves
All electromagnetic waves:
 travel at the speed (c) of 3 * 108 ms-1 in free space
 are transverse
 obey the laws of reflection and refraction
 show interference and diffraction effects
 can be polarized
 are unaffected by electric and magnetic fields
Example:
 Electromagnetic Wave diagram showing
relationship of the electric field, the magnetic
field, and the direction that the wave is moving. A
and B indicate points of maximum and minimum
field strength.
Electromagnetic Spectrum
 A ‘family of electromagnetic waves’ commonly referred
to as the electromagnetic spectrum. The
electromagnetic spectrum ranges from the short
wavelength (high frequency) gamma rays to the long
wavelength (low frequency) radio waves. A picture is
shown on next slide of the electromagnetic spectrum.
Use of each type of E.M. Wave
Waves:
Major Uses:
 Gamma-rays
 In medicine- to sterilize
 X-rays

 Ultraviolet Radiation

 Infrared Radiation

 Microwaves
 Radio Waves


instruments, to kill cancerous
growths.
To ionize gases, to detect flaws
in metals, forgeries, broken
bones.
To kill bacteria, used in
fluorescent lighting.
In infrared-sensitive cameras to
detect diseases, in thermal
photocopiers.
Microwave cooking,
telecommunication links.
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