PHY138 – Waves, Lecture 8Today’s overview:

Total Internal Reflection Optical Fibres Images Formed by Flat Mirrors

Laser as seen on TV and movies

Real Laser Real Laser Shining Through a Cloud

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.)

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.

airwater

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.

Hot air near the ground

Temperature Inversion: Hot air above

Total Internal Reflection

Occurs when n2<n1 θc = critical angle.

When θ1 ≥ θc, no light is transmitted through the boundary; 100% reflection

1

2sinn

nc

An Optical Fibre

Quiz 2 O

S

1

2

3

4

mirror

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.)

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.

How an image is formed