Chapter 22

Why is it incorrect to say that the visible light spectrum consists of the colors red, orange, yellow, green, blue, indigo, and violet?

Why is it incorrect to say that the visible light spectrum consists of the colors red, orange, yellow, green, blue, indigo, and violet?

These colors represent only the general progression of colors within the visible spectrum. In reality, there is an infinite number of possible colors.

How does a color television screen produce colors other than red, blue, and green if those are the only colors emitted by the screen’s pixels?

Color television screens produce different colors by varying the intensities of the primary colors that they emit.

Why does a mix of different colors of paint tend to produce a brown or gray color?

The pigments in paints absorb different wavelengths of light. The more pigments (colors) that are mixed, the more wavelengths that are absorbed, producing darker tones.

Why is visible light usually discussed in the context of human vision?

Some animals can see portions of the electromagnetic spectrum that are not visible to humans.

In order of decreasing frequency, name the colors of the visible spectrum.

violet, indigo, blue, green, yellow, orange, red

What is the range of wavelengths within the visible light spectrum?

between 380 and 700 nm

(True or False) The longest wavelength of visible light is violet.

False. The longest wavelength of visible light is red.

Which type of light source relies on a heated filament?

incandescence

The endpoint of a light ray is at the light’s ________, and its direction is ________ to the light’s wavefront.

source / perpendicular

Give two examples of luminous objects and two of illuminated objects.

Luminous objects: lamps, flashlights, candles, stars, and bioluminescent organisms;

Illuminated objects: any objects that can only reflect light, not produce it

Compare incandescent and fluorescent light bulbs.

Incandescent bulbs produce light through the heat generated by a filament’s resistance to electrical current.

Fluorescent light bulbs give off light when a powdered coating inside the bulb glows after being struck by UV light produced by an electric current flowing through mercury vapor.

Relate chemiluminescence and bioluminescence.

Chemiluminescence is light produced by chemical reactions. Bioluminescence is a form of chemiluminescence produced by living things.

Identify each of the following examples as either transparent, translucent, or opaque.

eyeglasses and air

transparent

Identify each of the following examples as either transparent (TP), translucent (TL), or opaque (O).

fog and wax paper

translucent

Identify each of the following examples as either transparent (TP), translucent (TL), or opaque (O).

wood paneling

opaque

What is the reference line used for measuring angles of incidence and reflection?

the normal

Which side of a concave mirror is reflective?

the inside

Describe the image created by convex mirrors.

Convex mirrors produce upright, reduced, virtual images.

Light reflecting from you strikes a nearby rock. Why don’t you see your image reflected on the rock?

The material in the rock scatters reflected light rays, producing diffuse reflection.

An incident ray strikes a convex mirror at an angle of incidence of 53°. What is the angle of reflection?

53°

Under what conditions does a concave mirror produce a real image?

A concave mirror produces a real image if the reflected object is farther from the mirror than the mirror’s focal point.

Under what conditions does a concave mirror produce a virtual image?

A virtual image is produced if the reflected object is between the mirror and its focal point.

Why would a convex mirror not be useful for creating a searchlight?

Searchlights make use of concentrated beams of light. Convex mirrors cause reflected rays to diverge, not converge.

Why can a convex mirror never produce a real image?

The rays reflected by a convex mirror diverge, that is, they never intersect.

Why does light refract?

When light travels from one medium to a different medium, the light’s speed changes, causing the light to bend.

You are looking at a lens with two convex surfaces. Is this a converging or diverging lens?

converging

What causes nearsightedness?

The shape of the eye and its lens causes light to focus in front of, rather than on, the retina.

Why is a material’s index of refraction always greater than 1?

The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in the material. Since the speed of light in a vacuum is the fastest light speed possible, the numerator in the ratio is always the larger of the two values. The resulting fraction thus always has a value greater than 1.

The index of refraction for material A is 1.005, and that of material B is 2.150. In which material does light travel faster? Explain.

Light travels faster in material A. The closer a material’s index of refraction is to 1, the closer the speed of light in that material is to the speed of light in a vacuum.

Explain how the reflected image in the photo at left is possible.

The reflected image of the jellyfish is explained by total internal reflection. The light rays reflected from the jellyfish strike the water-air boundary at an angle in excess of the critical angle and are reflected back into the water instead of passing into the air.

Why do we use a diverging lens to correct nearsightedness?

The eye lens focuses light in front of the retina in nearsightedness. The diverging lens spreads the light enough that the eye lens will then focus the light onto the retina.