ch31_jdzr

Zach Rosinger Jon Difiore Pd. #8

**Chapter 31 Review Diffraction and Interference:**
Christian Huygens was a Dutch mathematician-scientist in the late 1600s. This man proposed the concept that light waves spread out from a point source and can be regarded as overlapping tiny secondary wavelets, and every point on a wave can be regarded as a new point for a new wave. **
 * 31.1 Huygens' Principle:



Diffraction** is considered to be any bending of a wave by means other than reflection or refraction. This occurs when a wave starts out as a straight line, and goes through a slit in a wall or other barrier that causes the wave to bend on its way past. When light goes through an opening or slit, the opening is much larger than lights wavelength, which is why a shadow is cast. The amount of diffraction depends on the size of the wavelentgh compared to the size of the of the obstruction that is casting the shadow. FM radio waves are shorter than AM, and therefore don't diffract as much around buildings, which means that AM is recieved better inside buildings. Diffraction poses a problem when people are trying to use microscopes to see small objects. This poses a problem because if the size of the object is the same as the wavelength of light, the image will be very blurry because of the diffraction.
 * 31.2 Diffraction:

When waves intersect and cross eachother it is called an interference pattern. Waves from this point can either be increased, decreased, or neutralized. When the crest of one wave overlaps the crest of another, the two add together to create a //constructive interference// which is larger than the two individual waves. When the crest of one wave overlaps with the trough of another, the overall product is reduced creating a //destructive interference// pattern.
 * 31.3 Interference:**

In 1801, a British physicist and physician Thomas Young discoverd that when //monochroatic light// which is light of just a single color, was directed through two closely spaced pinholes, fringes of brightness and darkness were produced on a screen located behind. The bright spots were caused from when light waves from both pinholes arrived at a crest to crest pattern. The dark areas were formed from the light from both pinholes arriving in a crest to trough pattern. **Diffraction Grating** is a multitude of closely spaced parallel slits that are used to do the very same thing that Young discovered.
 * 31.4 Young's Interference Experiment:**

Interference fringes can be produced by the reflection of light from two surfaces that are close together. This can be seen on a rainy day at a gas station when there is gas on the ground and it is light out. There are visible colors on the ground where the oil is, which is caused because oil and water have different densities and the light passes through both of them. You can also test the flatness and curvature of a lens by placing it on a flat surface of glass and shining a light through, these patterns that you will be able to see on the glass lens will allow you to find the pattern of the curvature and assure it is correct.
 * 31.5 Single-Color Interference from Thin Films:**

Irridescence** occurs when light waves of mixed frequencies all come together. A thin film could be anything even as simple as a bubble because it has two closely spaced surfaces. Light reflects off of the first surface and some of it is reflected, where the rest goes through to the second surface, creating a colored effect. The different thiknesses of the film determine the color reflected because of the different wavelengths of light waves. //Inferometers// are instruments that are used to measure the extremely small distances between interference patterns and waves.
 * 31.6 Iridescence from Thin Films:

Incoherent** light is commonly emitted by a lamp. That means that the light has many phases of vibration and frequencies. A beam of light can be filtered so that it is //monochromatic// meaning that it has only one frequency, but it is still considered to be incohearent because the waves are out of phase and still continue to interfere with each other. A beam of light that has the same frequency, phase, and direction is **cohearent** light and there is no interference between its waves. Cohearent light is made by a **laser.** In a laser, the light wave is emitted by one atom and it stimulates the emission of light from the atom next to it. All of the atoms need to be the same type, which would create the exactness in color and the sharp, clear point. Lasers don't actually produce energy, they actually convert it from other energy.
 * 31.7 Laser Light:

A hologram** is a 3D version of a picture that contains the entirety of the picture in every portion of the hologram's surface. A hologram is produced by the interference between two laser light beams on a photographic film. If a hologram is produced on a film, and then the film is cut in half, it is still visible in its full design on both halves of the film.
 * 31.8 The Hologram: