PHY138 – Waves, Lecture 8 Today’s overview:

1. PHY138 – Waves, Lecture 8Today’s overview: • Total Internal Reflection • Optical Fibres • Images Formed by Flat Mirrors Real Laser Shining Through a Cloud Real Laser Laser as seen on TV and movies

2. Reading Assignment • Please read the following from Serway and Jewett before class on Monday: Chapter 26, Sections 26.4 - 26.6 and Context 7 Conclusion on page 1037. • A www.masteringphysics.com assignment is due this Friday at 5:00 PM. It is the last Mastering Physics assignment of the semester. (hoot.)

3. air water A fish swims below the surface of the water. An observer sees the fish at: 1. a greater depth than it really is. 2. its true depth. 3. a smaller depth than it really is.

4. Notes from last lecture • The index of refraction, n, of air depends on temperature; n decreases as air Temperature increases • When a ray enters a layer of different n, it bends • If n decreases, the ray bends away from the normal. This is refraction. • Refraction effects cause mirages, twinkling of starlight, and “heat currents” off hot highways or other surfaces.

5. Hot air near the ground

6. Temperature Inversion: Hot air above

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

8. An Optical Fibre

9. mirror Quiz 2 O 1 3 An observer O, facing a mirror, observes a light source S. Where does O perceive the mirror image of S to be located? (5 = none of the points shown.) 4 S 2

10. 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.

11. How an image is formed