Copy of Physics - Chapter 16 - Mirrors and Lenses

Part A. Can you see a virtual image? Part B. Can you photograph one? Explain your answers.

• A. A. yes; B. No, an image from a flat mirror cannot be photographed.
• B. A. no; B. Yes, an image from a flat mirror can be photographed.
• C. A. yes; B. Yes, an image from a flat mirror can be photographed.
• D. A. no; B. No, an image from a flat mirror cannot be photographed.

State the law of reflection.

• A. ϑ_r=ϑ_i, where ϑ_r is the angle of reflection and ϑ_i is the angle of incidence.
• B. ϑ_r>ϑ_i, where ϑ_r is the angle of reflection and ϑ_i is the angle of incidence.
• C. ϑ_r<ϑ_i, where ϑ_r is the angle of reflection and ϑ_i is the angle of incidence.
• D. ϑ_r=0, where ϑ_r is the angle of reflection.

Does light change direction toward or away from the normal when it goes from air to water? Explain.

• A. The light bends away from the normal because the index of refraction of water is greater than that of air.
• B. The light bends away from the normal because the index of refraction of air is greater than that of water.
• C. The light bends toward the normal because the index of refraction of water is greater than that of air.
• D. The light bends toward the normal because the index of refraction of air is greater than that of water.

An object is positioned in front of a lens with its base resting on the principal axis. Describe two rays that could be traced from the top of the object and through the lens that would locate the top of an image.

• A. A ray perpendicular to the axis and a ray through the center of the lens
• B. A ray parallel to the axis and a ray that does not pass through the center of the lens
• C. A ray parallel to the axis and a ray through the center of the lens
• D. A ray parallel to the axis and a ray that does not pass through the focal point

A person timing the moonrise looks at her watch and then at the rising moon. Describe what happened inside her eyes that allowed her to see her watch clearly one second and then see the moon clearly.

• A. The shape of the lens was changed by the sclera, and thus its focal length was also changed, so that each of the images focused on the retina.
• B. The shape of the lens was changed by the choroid, and thus its focal length was also changed, so that each of the images focused on the retina.
• C. The shape of the lens was changed by the iris, and thus its focal length was also changed, so that each of the images focused on the retina.
• D. The shape of the lens was changed by the muscles, and thus its focal length was also changed, so that each of the images focused on the retina.

For a concave lens, if the image distance, d_i, is negative, where does the image appear to be with respect to the object?

• A. The image always appears on the same side of the lens.
• B. The image appears on the opposite side of the lens.
• C. The image appears on the opposite side of the lens only if the object distance is greater than the focal length.
• D. The image appears on the same side of the lens only if the object distance is less than the focal length.

Why are diverging mirrors often used for rear-view mirrors in vehicles? What is the main disadvantage of using such a mirror compared with a flat one?

• A. It gives a wide range of view. The image appears to be closer than the actual object.
• B. It gives a narrow range of view. The image appears to be farther than the actual object.
• C. It gives a narrow range of view. The image appears to be closer than the actual object.
• D. It gives a wide range of view. The image appears to be farther than the actual object.

A high-quality diamond may be quite clear and colorless, transmitting all visible wavelengths with little absorption. Explain how it can sparkle with flashes of brilliant color when illuminated by white light.

• A. Diamond and air have a small difference in their refractive indices that results in a very small critical angle. The light that enters a diamond may exit at only a few points, and these points sparkle because many rays have been directed toward them.
• B. Diamond and air have a small difference in their refractive indices that results in a very large critical angle. The light that enters a diamond may exit at only a few points, and these points sparkle because many rays have been directed toward them.
• C. Diamond has a high index of refraction with respect to air, which results in a very small critical angle. The light that enters a diamond may exit at only a few points, and these points sparkle because many rays have been directed toward them.
• D. Diamond has a high index of refraction with respect to air, which results in a very large critical angle. The light that enters a diamond may exit at only a few points, and these points sparkle because many rays have been directed toward them.

The most common type of mirage is an illusion in which light from far-away objects is reflected by a pool of water that is not really there. Mirages are generally observed in deserts, where there is a hot layer of air near the ground. Given that the refractive index of air is less for air at higher temperatures, explain how mirages can be formed.

• A. The hot layer of air near the ground is lighter than the cooler air above it, but the difference in refractive index is small, which results in a large critical angle. The light rays coming from the horizon strike the hot air at large angles, so they are reflected as they would be from water.
• B. The hot layer of air near the ground is lighter than the cooler air above it, and the difference in refractive index is large, which results in a large critical angle. The light rays coming from the horizon strike the hot air at large angles, so they are reflected as they would be from water.
• C. The hot layer of air near the ground is lighter than the cooler air above it, but the difference in refractive index is small, which results in a small critical angle. The light rays coming from the horizon strike the hot air at large angles, so they are reflected as they would be from water.
• D. The hot layer of air near the ground is lighter than the cooler air above it, and the difference in the refractive index is large, which results in a small critical angle. The light rays coming from the horizontal strike the hot air at large angles, so they are reflected as they would be from water.

When you focus a camera, you adjust the distance of the lens from the film. If the camera lens acts like a thin lens, why can it not be kept at a fixed distance from the film for both near and distant objects?

• A. To focus on a distant object, you need to increase the image distance.
• B. To focus on a distant object, you need to increase the focal length of the lens.
• C. To focus on a distant object, you need to decrease the focal length of the lens.
• D. To focus on a distant object, you may need to increase or decrease the focal length of the lens.