In this lecture you will:
|Type of waves||Main interaction||SOUND||LIGHT (EMS)|
|INTERFERENCE||Run into each other||acoustics (loud/soft)||holograms (bright/dark)|
|REFLECTION||Hit and bounce off surfaces||acoustics: echoes and reverberations||mirrors, colors, shiny and matte|
|REFRACTION||Enter clear materials and bends||rumble of thunderstorms||lenses, diamonds, rainbows|
|DIFFRACTION||Bend around solid or little slit||how we hear around a post||slits, rainbow effect on CD or DVD|
|This is what happens when waves hit a
solid object and bends around it. It is similar to the way
waves of water hit the opening in breakers.
When sound hits a small object, or goes thru an opening the waves bend. What happens later is the waves may run into each other and interfere, but the BENDING is due to DIFFRACTION.
This is why sound can be heard in another
room thru the door without standing right in front of it, the waves of
sound bend around the opening.
|When there is a narrow opening light moves
as a wave, hits the narrow opening and bends around it which produces a
"In his 1704 treatise on the theory of optical phenomena (Opticks), Sir Isaac Newton wrote that "light is never known to follow crooked passages nor to bend into the shadow". He explained this observation by describing how particles of light always travel in straight lines, and how objects positioned within the path of light particles would cast a shadow because the particles could not spread out behind the object."
"On a large scale, this hypothesis is supported by the seemingly sharp edges of shadows cast by rays from the sun. However, on a much smaller scale, when light waves pass near a barrier, they tend to bend around that barrier and spread at oblique angles. This phenomenon is known as diffraction of the light, and occurs when a light wave passes very close to the edge of an object or through a tiny opening, such as a slit or aperture. The light that passes through the opening is partially redirected due to an interaction with the edges."
Hold a razor blade or a sewing needle to light and you can see the waves bend when coming through the slit opening, or, project that onto paper.
- diffraction grating separates
light into spectrum
|"In optics, a diffraction grating is an optical component with a periodic
structure, which splits and diffracts light into several beams travelling
in different directions. The directions of these beams depend on the spacing
of the grating and the wavelength of the light so that the grating acts
as the dispersive element. Because of this, gratings are commonly used
in monochromators and spectrometers."
Your spectrometer (spectrophotometer, spectrograph or spectroscope) uses a diffraction grating to split light into the visible spectrum.
Diffraction grating seen on cd or dvd
|loud and soft areas of sound in concerts||sound interference|
|bright or dim areas lined up in a row on a surface||light interference|
|holograms||light interference using lasers|
|colors||light reflection and absorption|
|shiny or matte||light reflection and interference|
|soap bubbles and oil spill rainbows||light reflection and interference|
|the rumble of thunder||sound refraction|
|prism rainbow||light refraction|
|rainbows||light refraction and reflection|
|diamonds twinkle||light refraction and reflection|
|blinding early morning light||reflection less than critical angle 50o|
|hearing around corners||diffraction|
|rainbow effect on DVDs||diffraction|