Chapter 29

What accounts for the light and dark bands produced when monochromatic light reflects from a glass pane atop another glass pane?

Interference from the light reflected from the air -glass interfaces on the top and bottom of the air gap between the glass panes

What causes the spectrum of colors seen in gasoline splotches on a wet street? Why are these not seen on a dry street?

It is caused by the interference of light waves reflected from the top of the gasoline layer and the bottom where the gasoline floats on water. The dry surface is rough and interference works best with a flat-topped layer of water.

When ordinary light is incident at an oblique angle upon water, what can you say about the reflected light?

More of the reflected light is polarized horizontally

If you were a rock climber, would you want to wear the same glasses to prevent glare as you did when you were driving, and why?

No. While you were driving, the polarization angle of your glasses was aligned vertically to block horizontal glare from the road. For the glasses to block vertical glare from the rock face, the polarization angle would have to be aligned horizontally.

Some double-pane airplane windows darken when the inner pane is rotated. The panes are

Polaroid filters

Light is a form of electromagnetic wave, containing oscillating electric and magnetic fields. Select Add Detector, which shows how the electric field oscillates in time at the location of the probe. The amplitude of the wave at the location of the probe is equal to the maximum electric field measured. How does the amplitude of the wave depend on the distance from the source?

The amplitude decreases with distance

Compare the distances from the first location nearest the middle of the screen where the intensity is nearly zero (dark fringe) to each of the two slits. How do the distances compare?

The difference in the distances is equal to half the wavelength of the wave

Now, measure the distance from the first bright fringe above the middle of the screen to the upper slit. Call this distance r1. Next, measure the corresponding distance to the lower slit, r2. The distances r1 and r2 are shown in the figure for clarity. How do the distances r1 and r2 compare?

The difference in the distances is equal to the wavelength of the wave.

How does the distance between consecutive bright fringes depend on the slit separation?

The fringes get closer together as the slit separation increases

How does the distance between consecutive bright fringes depend on the wavelength of the light?

The fringes get farther apart as wavelength increases

Now, select Two Slits and a slit separation of roughly . (Keep the slit widths and barrier location the same as in Part C, and be sure the amplitude is still set to the highest setting). Which statement best describes how the intensity of light on the screen behaves?

The intensity is large near the middle of the screen, then decreases to nearly zero, and then increases again as the distance from the middle of the screen increases.

Now, select a barrier with one slit, and use the Barrier Location slider bar to place it roughly away from the light source (second tick mark on the slider bar). Adjust the slit width (using the slider bar) to roughly (first tick mark). Keep the wavelength of the light set to red. Which statement best describes how the intensity of the wave depends on position along the screen?

The intensity is roughly constant

Select Show Screen to place a screen on the right edge of the panel. You might also want to select the Plot Intensity graph to see the details more clearly. Which statement best describes how the intensity of the wave depends on position along the screen?

The intensity is roughly constant

Will light pass through a pair of Polaroids when the axes are aligned? When the axes are at right angles to each other? Why?

The light that passes through the first Polaroid comes out completely polarized in the direction of that polarizer, so it easily passes through the analyzer with an aligned axis but not through one with an axis at right angles.

How does the distance between the bright fringes depend on the amplitude of the wave?

The spacing of the fringes does not change when the amplitude changes (just the brightness changes).

How does the distance between the bright fringes depend on the slit width (for slit widths less than the wavelength of the light)?

The spacing of the fringes does not change when the slit width changes

Is parallax evident when you close one eye? Why?

The view through one stationary eye shows no parallax, because it takes two different views to see parallax.

Will plane waves incident upon a small opening in a barrier fan out on the other side or continue as plane waves?

They will fan out and decrease in amplitude

When light bounces off a surface, which component will be reflected more - the component that is parallel to the surface, or the component that is perpendicular to the surface, and why?

We can expect the component that is parallel to the surface to reflect more, because it aligns with the surface - similar to a flat rock bouncing off the surface of water.

Suppose that we introduce a second polarizer into the experiment. Rank, from greatest to least, the intensity of the microwave radiation at the receiver for the five configurations shown below. (The polarizers are shown obliquely from the side.)

*Greatest* D & E C A & B *Least*

Does interference occur when water or sound waves encounter a barrier with two slits?

Yes, interference also occurs for both of these types of waves

When waves from a pair of closely-spaced slits arrive out of phase

a dark fringe is produced

When you view color in a soap film with sunlight in back of you, a friend on the other side of the soap film likely sees

a different color

The electric vectors that make up polarized light are

aligned

Three-dimensional viewing normally involves

all of the above (an ability to see 'around' things, parallax, two-eye vision)

Secondary wavelets spread from a wave with

an unchanging speed

Interference effects are less visible for thick films because the reflected waves

are too displaced to interfere

Light travels through non-cubic transparent crystals

at different speeds along different optic axes

The polarization axes of glasses for 3-D viewing are

at right angles to each other

A double-slit arrangement produces interference fringes for yellow sodium light. To produce narrower-spaced fringes, should red light or blue light be used?

blue light

Newton's rings will be closer together if illuminated with

blue light

When the reflected path from one surface of a thin film is one full wavelength different in length from the reflected path from the other surface and no phase change occurs, will the result be destructive interference or constructive interference?

constructive interference

Any bending of light that is not reflected or refracted is due to

diffraction

What kind of glasses would you wear while watching 3D movies, and why?

glasses with one horizontally polarized and one vertically polarized lens, because one projector is horizontally polarized and the other is vertically polarized

A thin film appears magenta when illuminated with white light. The color being cancelled by destructive interference is

green

For radio reception in city buildings, diffraction is

helpful

Light reflecting from a horizontal surface is likely to be polarized

horizontally

Which will give wider-spaced fringes, a double-slit experiment in air or in water? (Let the figure guide your thinking.)

in air

A diffraction grating separates light into its component colors by the process of

interference

A hologram is the result of light

interference

Reinforcement and cancellation are terms common to wave

interference

The iridescent colors seen in thin films are the result of

interference

The amount of light from an incandescent lamp that is transmitted through an ideal Polaroid filter is half, and through a classroom Polaroid filter is

less than half

Diffraction from foghorns is best if the waves being diffracted are

long

A razor blade nicely shows diffraction fringes when illuminated with

monochromatic light

Waves spread when passing through openings of various sizes. More spreading occurs for openings that are

narrow

A painting looks less flat when viewed with

one eye

Huygens' principle features wavefronts that are composed of

overlapping waves

A glass prism separates light into its component colors by the process of

refraction

To remove the glare of light from a polished floor, should the axis of a Polaroid filter be horizontal or vertical?

vertical

When light with both horizontal and vertical components is incident on a vertical side of a stone cliff, which component of light is more strongly reflected?

vertical component

Light illuminates two closely spaced thin slits and produces an interference pattern on a screen behind. For which color of light - yellow or green - will the distance between the fringes be greater?

yellow

Does parallax underlie the depth perceived in stereo views?

All of the above (Yes. Presenting two different views, one to each eye, mimics parallax and allows the brain to perceive three dimensions, Yes. Moving one or both eyes sideways relative to a scene allows the brain to perceive the scene in three dimensions, Yes. Moving a scene to the side relative to an observer or rotating a scene allows the brain to perceive it in three dimensions)