Ch+24+-+Diffract+and+Interfere

__**Diffraction and Interference**__ - These two ideas mainly focus on the idea of light moving in waves. Otherwise known as wave optics.-

__ -Evidence of Interference in the world include a rainbow spectrum created by bubbles. Also, a purple hue or haze created by various camera lenses. __**__ - Conditions for interference to occur: __**__ 1.) The wavelengths of the waves must be near or exactly identical 2.) The waves must be relatively constant in phase with each other.
 * __ Interference __**

To create the interference, two sources of light are needed. Alng with that, the light being emitted from the sources need to maintain a constant phase. An excellent experiment to display the two source, interference can be seen in Young's Double-Slit Experiment. __

The images display light moving as waves through the two slits. In the images, the waves of light are moving towards a screen or back wall. As the waves are moving, there are two types of interference going on. This includes constructive and destructive interference. Constructive interference is noted by the bright spots on the back screen. This is the waves constructing together to create a strong point. Destructive interference is noticed at the spots that are dim and not lit, or dark spots. These are the spots where the waves of light were destructive and did not combine to create a light spot. The light and dark spots can be noticed in the image below. To the far right, there are dark lines where the destructive interference happens, and on the contrary, bright lines where the constructive interference takes place.

**Theory and Math** Of course when the light is not being observed on the center mark directly in front of the slits, there will be some obvious path difference lengths created by the extra travel distance of light from one of the slits. The path difference can be determined by the following equation: **Delta (path difference) = r1 + r2 = dsin**

The path difference found also helps determine weather the waves are in phase or not when they arrive at the destination. Therefore if they are in phase, they will create the constructive interference as stated before. A path difference of zero can denote constructive.


 * Delta (path difference) = m (lamda)

__ Thin Film Interference: __**__ A prime example of interference in thin films id with bubbles and oil slicks. The variety of colors that are seen are created by reflected waves of light from the opposite surface of the film. When this happens, there are two things that need to be noted to determine weather or not the waves are constructive or destructive... 1.) An electromagnetic wave traveling from a medium to another medium undergoes a 180 degree phase change when N2 > N1 and undergoes no phase change when N2< N1. 2.) The light's wavelength in a medium with an index of refraction, is (lamda) = (lamda)/(n)

Other than applying these two rules, Newton threw some input into the topic of thin film interference. This is known as Newton's Rings. This method includes placing a planoconvex lens onto a flat glass surface. Due to the air gap between the lens and surface, and the distance from the lens, a pattern of light and dark rings can be noticed. These patterns are created due to the combination of Ray 1 reflected from the plate with Ray 2 which is reflected from the lower surface. Ray 1 experiences phase change and Ray 2 experiences none. So looking back at the two rules, the thin film interfernce will occur. __



**Polarization:**

It is known that in the world of physics, that electromagnetic waves are at right angles to each other as well as to the the direction of wave propagation. A wave is said to be polarized if the electric field vibrates in the same direction at all times at a single point. Then, there is a plane created by the electric field and the propagation and this is known as //the plane of polarization//. It is in fact possible to get polarized light from unpolarized beams by removing the waves from the field except for the ones oscillating in a single plane. Eventually, a polaoid or polarizer was created by EH Lands. This is a sheet of long-chain hydrocarbons. When the vibrating light tries to get through the polarizers, some of the light is blocked. The light that is blocked is the waves moving perpendicular to the grating of hydrocarbons. On the other hand, the parallel waves make it through. When two of these polarizers are used together, the light can be blocked completely. Use of this technology in the real world can be found in some polarized sunglass lenses. These lenses are made to block glare created by reflecting surfaces of the earth. When wearing a pair of these, and glare is still experienced, try a simple tilt of the head. Is the glare gone? Should be. The rays were blocked by the polarized technology. The image below is just an example of how polarized lenses enhance the images seen around.




 * All images found and used were picked up from wikipedia. There it said I had full privelege and right to distribute, copy, and use.**