10.+Light,+Interference,+and+Diffraction

=  Interference and Diffraction﻿ ﻿ ﻿ ﻿﻿  = = ﻿ ﻿~Key Concepts =
 * Incoherent light illuminates an object evenly, just as a lightbulb illuminates your desk.
 * Only the superposition of light waves from cohernet light sources can produce an interference pattern.
 * Interference demonstrates that light has wave properties.
 * Light passing through two closely spaced, narrow slits produces a pattern on a screen of dark and light bands called interference fringes.
 * Interference patterns can be used also to measure the wavelenght of light.

 ﻿ ﻿*** Thomas Young***
 * **Date of Birth: June 13th, 1773**
 * **Date of Death: May 10th, 1829**
 * <span style="color: #36e262; font-family: 'Comic Sans MS',cursive; font-size: 120%;">**Place of Birth: Milverton, United Kingdom**
 * <span style="color: #36e262; font-family: 'Comic Sans MS',cursive; font-size: 120%;">**Profession: Physicist and physician**
 * <span style="color: #36e262; font-family: 'Comic Sans MS',cursive; font-size: 120%;">**Education: London**

**<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 18pt; line-height: 115%;">Samuel Tolansky ** · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">Samuel Tolansky was born November 17, 1907. **  · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">He was born in Newcastle. **  · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">He was educated at Rutherford College from 1919-1925, followed by three years of study at Durham University. **  · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">Tolansky performed a significant amount of his research and developed the interference contrast microscopy technique that bears his name. **  · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">He carefully investigated the intensity distribution of fringes that appear as a result of multiple-beam interference. **  · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">In Tolanksy's technique the surface of the reference plate and the specimen are coated with a highly reflective film. **  · **<span style="color: #953735; font-family: 'Times New Roman','serif'; font-size: 14pt; line-height: 115%;">The reflective surfaces of the microscope are situated so that the distance between them is as minute as possible, and incident light beam is collimated to a parallelism within 3 degrees and made nearly perpendicular to the reference plate. **  ﻿﻿ **<span style="color: #f0790f; font-family: 'Comic Sans MS',cursive; font-size: 170%;">﻿*Vocabulary* ** **<span style="color: #f0790f; font-family: 'Comic Sans MS',cursive;">~__Incoherent Light__: Light with unsynchronized wave fronts that illuminates objects with an even, white light. ** **<span style="color: #f0790f; font-family: 'Comic Sans MS',cursive;">~__Coherent Light__: Light from two or more sources, whose additive superposition produces smooth wave fronts. ** **<span style="color: #f0790f; font-family: 'Comic Sans MS',cursive;">~__Interference Fringes__: A pattern of light and dark bands on a screen, resulting from the constructive and destructive interference of light waves passing through two narrow, closely spaced slits in a barrier. ** **<span style="color: #f0790f; font-family: 'Comic Sans MS',cursive;">~__Monochromatic Light__: Light having only one wave length. ** **<span style="color: #f0790f; font-family: 'Comic Sans MS',cursive;">~__Thin- Film Interference__: A phenomenon in which a spectrum of colors is produced due to the constructive and destructive interference of light waves reflected in a thin film. **
 * <span style="font-family: 'Comic Sans MS',cursive; font-size: 120%;">﻿**Young discovered the cause of astigmatism in 1801, which was about the time that he began his study of light.**
 * <span style="color: #a71ce9; font-family: 'Comic Sans MS',cursive; font-size: 120%;">**Thomas applied his new wave theory of light to explain the colors of thin films such as soap bubbles,and by relating color to wavelength.**
 * <span style="color: #a71ce9; font-family: 'Comic Sans MS',cursive; font-size: 120%;">**He calculated the approximate wavelenghts of the seven colors recognized by Newton.**
 * <span style="color: #a71ce9; font-family: 'Comic Sans MS',cursive; font-size: 120%;">**He was also the 1st scientist to give the word "energy" it scientific connotation.**
 * <span style="color: #a71ce9; font-family: 'Comic Sans MS',cursive; font-size: 120%;">[[image:samuel.jpg]]

**<span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 150%;">﻿ <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 170%;">﻿~Interference Of Coherent Light~ ** **<span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">﻿ <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive;">﻿ ** ﻿ ﻿ <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">﻿> **Fundmentals of Interference:**

> <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">> **Measuring the Wavelenght of Light** > **> Equation for Wavelength from Double- Slit Experiments: Follow link below!!!!!** > **__ [] __** > <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">﻿> **Example of interference of light by a double slit>** > > (Click [|here] ||
 * <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">**Wave properties of light lead to interference. Certain conditions of coherence must be met for these interference effects to be readily visible.**
 * <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">**The image formation in the microscope relies on a complex interplay between interference and diffraction.**
 * <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">**When light is passing through the specimen is scattered and diffracted into divergent waves by tiny details and features present in the specimen.**
 * <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">**Some may observe some type of optical interference almost everyday. Usually not realized the events in play behind the often display of color produced when light waves interfernce with each other.**
 * <span style="color: #f25f62; font-family: 'Comic Sans MS',cursive; font-size: 110%;">**Many people studied and found theories on interference such as: Augustin-Jean Fresnel (1788-1827), Christiaan Huggens (1629-1695), Samuel Tolansky (1907-1973), and Thomas Young (1773-1829).**
 * [[image:http://www.physchem.co.za/OB12-wav/Graphics/diffraction1.gif width="200" height="200"]] || [[image:http://www.physchem.co.za/OB12-wav/Graphics/diffraction2.gif width="199" height="200"]] ||
 * || [[image:http://www.physchem.co.za/OB12-wav/Graphics/two_slits.gif width="334" height="254"]] ||
 * [[image:http://www.physchem.co.za/Common%20Files/think1.gif]] || What is meant by "polarized light"?

<span style="color: #4f81bd; font-family: 'Constantia','serif'; font-size: 18pt; line-height: 115%; margin: 0in 0in 10pt;">Thin-Film Interference · <span style="color: #4f81bd; font-family: 'Constantia','serif'; font-size: 12pt; line-height: 115%;">Constructive and destructive interference of light waves is the reason why thin-films show colorful patterns. · <span style="color: #4f81bd; font-family: 'Constantia','serif'; font-size: 12pt; line-height: 115%;">It is known as thin-film interference because the interference of light waves reflects off the top surface of a film with the waves reflecting from the bottom surface. · <span style="color: #4f81bd; font-family: 'Constantia','serif'; font-size: 12pt; line-height: 115%;">To obtain the nice colored pattern, the thickness of the film has to be on the order of the wavelength of light. Thin-film interference provides another line of evidence for the wave behavior of light.

<span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">Seven Review Questions <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;"> <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;"> <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;"> <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">1. When do the intensity of bright bands decrease? <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">2. What color is the band when all wavelengths interfere constructively in the central band? <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">3. What is the opposite of incoherent light? <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">4. When light passes through and is diffracted by the split, what does it produce? <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">5. What is the definition of monochromatic? <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">6. What is the formula of wavelength from double-slit experiment? <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;"> <span style="font-family: 'Times New Roman','serif'; font-size: 16pt; line-height: 115%;">