10 Phenomena of Waves

|SHM | Wave terms | Wave Phenomena | Extensions

propogation
absorption
reflection
refraction
interference
diffraction
scattering
dispersion
Doppler Effect
Polarization
propogation Waves don't move or travel - they propogate.
In mechanical waves, the medium is displaced from equilibrium as the wave passes, but the medium returns to equilibrium after the wave is gone. There is no net motion of the medium while the wave propogates from one place to another.
  absorption
(vs damping) 		As a wave propogates through a medium some of its energy can be lost within the medium. These might be frictional forces. How will you know that energy is being lost in a mechanical wave? ( gnisearced si edutilpma)
Damping is when an outside force takes the wave energy. shock absorbers on a car produce damping
reflection and refraction

The boundary between two media is called the interface. When wave energy reaches the interface some of the wave energy will stay in the first medium and some will propogate into the second medium. The wave that stays within the first medium is called the reflected wave. The wave that moves into the second medium is called the refracted wave. The greater the difference in the velocity of the two waves the more energy that is reflected. If v1 > v2 then the reflected wave will have a phase shift of 180° (f = p ; completely out of phase) compared tothe original wave (called the incident wave). If v1 < v2 then the reflected wave will have a phase shift of 0°, and the reflected wave and the incident wave will be in phase.

reflection applet

  interference

When two or more waves are at the same point in a medium at the same time they interfere with each other. If a crest meets a crest (a crest is superimposing on another crest) the interference is said to be constructive where the result is a "super crest". If a crest meets a trough the intereference is called destructive where the result is a node.

Christian Huygens gave a formal explanation using Huygens' Principle of Superposition that said that when two waves superimpose on each other (are at the same place in the medium at the same time) the resulting wave's amplitude is the algebraic sum of the individual amplitudes. If two waves interefere and have amplitudes of 2 cm and 3 cm then the resulting wave will have an amplitude of 5 cm (constructive intereference). If the two interfering waves have an amplitude of 3 cm and -2 cm the resulting wave will have an amplitude of 1 cm (destructive interference).
Interference applet

examples fromhttp://physics.bu.edu/~duffy/semester1/c21_int_reflections.html

reflection off of an open end where f = 0


reflection off of a fixed end where f = p/2


the wave goes from medium 1 to medium 2 by refraction as it passes through the interface (I); the second wave has a different velocity, amplitude, wavelength, but the same frequency.

 

angle of incidence = angle of reflection

examples from http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=35

the black wave is interfering with the blue wave to create the red wave

constructive interference


even more constructive interference


destructive interference

Doppler Effect

When the source and/or the receiver are in relative velocity there will be a change in the frequency at the receiver compared to the original frequency. The detected frequency will be higher than the original when the relative velocity of the source is toward the receiver. APPLET

source (red dot) is moving to the right; the waves in front of the source will have a higher frequency than the frequency produced by the source while the waves behind the source have a lower frequency. When the source moves faster than the wave a shock wave is created.


 diffraction

(Microscopic interference)
The bending of a wave as it goes through an opening or around an obstacle. The opening or obstacle should be approximately the same size as the wavelength.


 scattering (Microscopic reflection)
In some situations waves can reflected off of small obstacles so that most of the wave energy goes through the medium and only part of the energy is scattered. 		 dispersion (Microscopic refraction)
When waves move into a second medium and different frequency waves propogate at slightly different velocities, the waves will disperse. This often means that the waves will propogate in slightly different directions.
polarization (for transverse waves only)
It occurs when a transverse wave is allowed to oscillate in only one plane. Waves oscillating perpendicular to the plane of polarization will be blocked by the polarizer. Waves oscillating along a diagonal compared to the polarizer will allow the parallel component of the diagonal wave to go through while blocking the perpendicular component. 		 

 

last modified 2-14-07