ch31_lm

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**CHAPTER 31**
__**31.1- Huygen's Principle**__

Dutch scientist/ mathmetician, Christian Huygens, discovered something new about waves in the lat 1600's.

He found that light waves spreading from a point source may be seen as the overlapping of tiny secondary wavelets, and that any point on any wave may be regaurded as a new point source on a secondary wave.

To simplify this, he discovered that wave fronts are made up of tinier wave fronts.

This idea is now known as Huygens principle. As wave fronts spread, they appear less curved. In the diagram to the right, it shows how a very magnified veiw of a wave which is being made up by larger waves. Huygens law is also aplicable in refraction.


 * __31.2- Diffraction__**

Diffraction is defined as the bending of any wave by means of reflection or refraction. This quality of waves can be seen in all types of waves such as water, and even lights (see right).
 * When passing through an opening, plane waves bend outrwards into smaller spherical waves. Shorter waves (such as FM radio waves) do not diffract as widely as longer waves (such as AM radio waves).

__**31.3- Interference**__

Introduced previously in Chapter 25 and 26, wave interference is when two waves meet and combine. Constructive interference- the light areas are areas of the diagram, are areas of constructive interference Destructuve interference- the dark areas are places where destructive interference occours.
 * Two waves of the same frequency, are able to add togeher and make larger wave.
 * Two waves of opposite frequency, with equal amplitude will result in cancelation of the wave.
 * Two waves of different frequency, with different amplitude, will result in partia cancelation of the wave.


 * __31.4- Young's Interference Experiment__**

British physisist Thomas Young discovered that monochromatic light is directed through two closley spaced pinholes, produce fringes of light and dark are a screen behind it. Below is a diagram of showing the seriesof bright and dark lines which result from the different path lengths from the slit to the screen.
 * What results from this experiment, can be seen in the diagram to the left.


 * __31.5- Single Color Interference from thin films__**

When monochromatic light is reffected off of two surfaces that are //almost// parallel to eachother a different set of interference will result. Depending on the thickness of the objects at the given point, either constructive or destructive interference will result.

__**31.6- Iridescence of thin films**__ The position of thin-film interference fringes depend upon the wavelength of the light which is illuminating the object. As the wavelength of the light increases, the the width of the spacing between the fringes does as well. As the various colors come into constructive and destructive interference, the resulting colors which are observed at each point will be a combination of all of the colors many colors experiencing constructive interference there.
 * An example of this can be seen in the form of a soap bubble or gasoline spilled on a wet surface.

A Coherent light beam is defined as a beam of light with the same frequency, direction, and phase.
 * __31.7- Laser Light__**

A comomn example of this coherent light is a laser. Though a laser does not create energy, it delivers its energy output in a way that makes it seem to be very bright.
 * In a Beam of coherent light, there is no destructive interference.


 * It is not uncommon fot a laser to only put out less than 1% of the energy put in to it.


 * __31.8- The Hologram__**

A three-dimensional image of an object that contains an interference pattern created by spreading a laser beam so that one half of it shines on the object, and the other half of the beam shines on a piece of film is known more comonly as a **Hologram**.

When the two seperate parts of the beam combine on the film, they result in an interference pattern. If a similar beam of light shines on the developed hologram, the waves will then recreate the original waves which formed the interference pattern resulting in a three-dimensional view of the original object.

Works Cited [] and, the text book and, for the images, click on them and the website where I got them will show up