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PHY138 – Waves, Lecture 7 Today’s overview

PHY138 – Waves, Lecture 7 Today’s overview. The Ray Model of Light Reflection Refraction Total Internal Reflection Medical Fibrescopes. Reading Assignment. This week’s reading assignment from the text by Knight is: Chapter 23 , Sections 23.1-23.6

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PHY138 – Waves, Lecture 7 Today’s overview

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  1. PHY138 – Waves, Lecture 7Today’s overview • The Ray Model of Light • Reflection • Refraction • Total Internal Reflection • Medical Fibrescopes

  2. Reading Assignment This week’s reading assignment from the text by Knight is: Chapter 23, Sections 23.1-23.6 Suggested Chapter 23 Exercises and Problems for Practice: 11, 17, 19, 27, 39, 49

  3. Message from Dr. Savaria…. (again) • If you have a conflict with the Waves Test at 6:00-7:30 PM on Tuesday Dec.6 you must: • Send an email to phy138y@physics.utoronto.ca confirming that you wish to re-register, if you registered for the alternate sitting of Test 1. or • Visit April Seeley in MP129 or MP302 to register for the first time you will write in an alternate sitting. • The deadline for confirming / registering is today by 5:00PM!

  4. Wave Fronts and Rays • Wave fronts connect points of equal phase on an extended wave. • Rays show the propagation direction of waves, and are always perpendicular to wave fronts. • Rays travel in straight lines • At a boundary they can reflect (bounce off) and refract (penetrate) the different medium. • Ray angles are measured relative to surface normal.

  5. The Law of Reflection

  6. Specular vs. Diffuse Reflection • Specular Reflection • The surface is flat at distance scales near or above the wavelength of light • It looks “shiny”, like a mirror.

  7. Specular vs. Diffuse Reflection • Diffuse Reflection • The surface is rough at distance scales near or above the wavelength of light • Almost all surfaces reflect in this way.

  8. How an image is formed

  9. Virtual Image in a flat mirror • Light rays emerging from an object obey the law of reflection for the specular surface of a mirror • Our mind imagines that the rays emerge from points beyond the mirror. • This thing beyond the mirror is called an image. No light rays actually pass through the image, so it is “virtual”. • It is convenient to describe the size and location of the image as if it were an actual thing.

  10. Index of Refraction • v is the speed of light in a transparent medium. • c is the speed of light in a vacuum (c=3.00×108 m/s) • n is a dimensionless constant: n≥1

  11. Snell’s Law of Refraction

  12. Total Internal Reflection • Occurs when n2<n1 • θc= critical angle. • When θ1≥θc, no light is transmitted through the boundary; 100% reflection

  13. An Optical Fibre

  14. Medical Fibrescopes Video-laryngoscopy with a flexible fiberscope

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