-
7/30/2019 Waves 100
1/6
Waves - Transverse and Longitudinal Waves
A wavemay be defined as a periodic disturbance in a medium that
carries energyfrom one point to another.
All waves require a sourceand a mediumof propagation.
Waves may lose energy as they propagate through a dense medium
(attenuation).
Waves that radiate isotropically (uniformly in all directions)
from a source also loseintensity due to the fact that the energy
they carry is spread out over an increasinglylarge area. This is
known as the inverse square law.
There are two distinct types of waves: Longitudinaland
Transverse. Sound wavesare an example of longitudinalwaves while
electromagnetic waves, such as light,are examples of transverse
waves.
Transverse waves transfer energy in a direction perpendicular to
the direction ofthe disturbance in the medium. A vibrating string
is an example of a transversewave. Although all points on the
string itself are constrained to move only up anddown, wave pulses
move perpendicularly along the length of the string. Thewave
speedis the speed with which a pulse moves along the string.
A transverse wave may consist of more than one pulse. Transverse
wavesconsisting of many pulses result when the wave source
oscillates about someequilibrium position for long periods of time.
Under such conditions an initialpulse is followed immediately by
another pulse of opposite displacement. Aseries of such alternating
pulses is known as a wave train.
-
7/30/2019 Waves 100
2/6
If the oscillations are steady the resulting waveform is
periodic. If the oscillationsare harmonicin the series of pulses is
known as a harmonic wave train. All of the
electromagnetic spectrum, including light, consists of
transverse waves thatresult from harmonic oscillations in
molecular, atomic or nuclear structures.
Longitudinal waves are waves that transfer energy in the same
direction as thedisturbance in the medium of propagation. Like
transverse waves, longitudinalwaves may consist of single or
multiple pulses. All longitudinal waves consist ofregions of high
and low density known as condensations and rarefactions
thatoscillate around local positions of equilibrium parallel to the
path of energytransfer. Sound waves are longitudinal waves. Sound
waves propagating throughair consist of a series of pressure
fluctuations above and below atmosphericpressure.
-
7/30/2019 Waves 100
3/6
-
7/30/2019 Waves 100
4/6
Interference/Superposition - combining waves together in such a
manner as tocause either constructive (strengthen) or destructive
(lessen) effects.
=
=
A
A
A
A
A
A
A
A
2A
2A
Constructive Interference
+
+
Destructive Interference
-
7/30/2019 Waves 100
5/6
Diffraction bending of waves as they pass through narrow
openings or aroundsharp corners
Refraction the change of speed and direction that occurs when a
wave goes fromone medium to another.
Scattering what happens, in general, when waves interact with
matter. Reflectionthat does not obey the Law of Reflection, i.e.,
waves reflect at all angles.
Reflection - a form of scattering that may be described with a
simple geometricrelationship, i.e. angle of incidence equals angle
of reflection. Most wavesexperience a phase shift upon
reflection.
-
7/30/2019 Waves 100
6/6
Polarization orientation of oscillations in space with respect
to the disturbedmedium. Polarization is a property unique to
transverse waves. A polarized wavevibrates in a single plane is
space. Since longitudinal waves vibrate along theiraxis of
propagation, it is not possible to polarize a longitudinal wave.
Polarizationis an important factor in reflection, refraction, and
scattering of electromagnetic
waves.
It is interesting to note that while the behavior of both
acoustic and light wavesunder reflection, for instance, is the same
the physical cause is quite different ineach case.
Frequency, wavespeed and wavelength are related mathematically
by the
expression: v = f. The velocity a wave in a given media is fixed
and is related tothe physical characteristics (temperature,
density, etc.) of the media. Frequencyand wavelength, therefore,
are inversely proportional to each other, i.e.; higherfrequencies
correspond to shorter wavelengths.
Phase the orientation of wave pulses in space with respect to
the origin of thewave.
A
A
A
A
A
A
A
A
In Phase
Out of Phase
