Lecture 33

Summary

Ray approximation
Law of Reflection
Snell's law

Today's joke

Quiz bonus Ch. 33

Total internal reflection

Interactive refraction applet

swimming pool video
Example #1

Huygen's principle diagram

Huygen's Principle

Diagram
reflection & refraction
total internal reflection
Animated applet

Example #2

Dispersion

Rainbows

Interactive rainbow applet

Practice:
Try this additional example

Example #3

Prepare:
Read textbook sections 34-1 and 34-2 before the next lecture

[supplemental material]

halos and sun dogs

more on atmospheric optics

Green flash only rarely seen at sunset is caused by a competition between dispersive refraction and scattering in the atmosphere.

This photograph was taken from Torrey Pines, California on Jan. 7, 1996, by Andrew T. Young.

$Green flash only rarely seen at sunset is caused by a competition between dispersive refraction and scattering in the atmosphere$

More photos of halos
ice crystal display

This picture was taken at the south pole, and includes a great number of interesting optical effects created by pencil-shaped and plate-shaped ice crystals.

ice crystal diagram

These are the ice crystals responsible for some of the effects you see in the above photo

slight dispersion ice crystal display

This picture was taken in Alaska, and shows some color in the sun dogs and other effects that result from slight dispersion in ice.

Knight2 35.CQ.5
The electric field strength (the red dots indicate E is out of the page) in the figure is _______.

A. increasing
B. decreasing
C. not changing
Answer

POP5 25.29
A room contains air in which the speed of sound is 343 m/s. The speed of sound in the concrete walls is 1850 m/s. Find the critical angle for total internal reflection of sound at the concrete-air boundary.
A. 5.39°
B. 10.7°
C. 55.6°
D. 79.3°
Answer

GC6 tb24.6
When a beam of light (λ = 590 nm), originally traveling in air, enters a piece of glass (n = 1.5) its frequency
A. increases by a factor of 1.5.
B. decreases by a factor of 1.5.
C. remains the same.

Answer

Walker5e 26.83
You take a picture of a rainbow with an infrared camera, and your friend takes a picture at the same time with visible light. The rainbow's radius in the infrared picture is _____ than its radius in the visible-light picture.
A. greater than
B. less than
C. the same as
Answer

B. decreasing

The rate of change of electric flux, or the displacement current, plays the role of current for the production of the magnetic field. Using the right hand rule, a clockwise magnetic field is produced by a current that points into the page. That means the displacement current must point into the page, hence the rate of change of the electric flux must point into the page, and the out-of-the-page electric field must be decreasing.
solution equation

B. 10.7°

This low angle explains why concrete reflects sound so efficiently - nearly every angle of incidence results in sound reflection. It also partly explains why concrete walls are great sound insulators, because very little sound transmits from air into concrete.

C. remains the same.
The wave frequency always remains the same when it crosses a boundary. The speed and the wavelength each change, but not the frequency.

dispersion in a rain drop

A. greater than
As seen in Figure 26-52 (above), long-wavelength red light has a smaller index of refraction (higher wave speed) than violet light, and red light emerges from the rain drop at larger angle than violet light. That makes the outer radius of a rainbow red and the inner radius violet. Because infrared light has a longer wavelength than red light, we expect its radius to be outside the radius of the red portion of the rainbow. [This means the index of refraction for infrared light in water is even smaller (even higher wave speed) than the index of refraction for red light.] Likewise, if a photo were taken in the ultraviolet we expect the radius of the rainbow to be less than the radius of the rainbow in the visible-light picture.
rainbow formation diagram