Conceptual Questions

ssm Solution is in the Student Solutions Manual.

| 1 | In Figure 26-1a, suppose that a layer of oil were added on top of the water. The angle at which the incident light travels through the air remains the same. Assuming that light still enters the water, does the angle of refraction at which it does so change because of the presence of the oil? Explain.

| 2 | Two slabs with parallel faces are made from different types of glass. A ray of light travels through air and enters each slab at the same angle of incidence, as the drawing shows. Which slab has the greater index of refraction? Why?

| 3 | When an observer peers over the edge of a deep empty bowl, he does not see the entire bottom surface, so a small object lying on the bottom is hidden from view. However, when the bowl is filled with water, the object can be seen. Explain this effect.

| 4 | ssm Two identical containers, one filled with water (n = 1.33) and the other filled with ethyl alcohol (n = 1.36), are viewed from directly above. Which container (if either) appears to have a greater depth of fluid? Why?

| 5 | When you look through an aquarium window at a fish, is the fish as close as it appears? Explain.

| 6 | At night, when it’s dark outside and you are standing in a brightly lit room, it is easy to see your reflection in a window. During the day it is not so easy. Account for these facts.

| 7 | A man is fishing from a dock. (a) If he is using a bow and arrow, should he aim above the fish, at the fish, or below the fish, to strike it? (b) How would he aim if he were using a laser gun? Give your reasoning.

| 8 | Two rays of light converge to a point on a screen. A plane-parallel plate of glass is placed in the path of this converging light, and the glass plate is parallel to the screen. Will the point of convergence remain on the screen? If not, will the point move toward the glass or away from it? Justify your answer by drawing a diagram and showing how the rays are affected by the glass.

| 9 | A person sitting at the beach is wearing a pair of Polaroid sun-glasses and notices little discomfort due to the glare from the water on a bright sunny day. When she lies on her side, however, she notices that the glare increases. Why?

| 10 | You are sitting by the shore of a lake on a sunny and windless day. Your Polaroid sunglasses are not equally effective at all times of the day in reducing the glare of the sunlight reflected from the lake. Account for this observation.

| 11 | The dispersion of sunlight by a prism is discussed in connection with Figure 26-18. Is it possible to direct a mixture of colors into a prism and have sunlight emerge from it? If so, explain how this could be done.

| 12 | Refer to Figure 26-6. Note that the ray within the glass slab is traveling from a medium with a larger refractive index toward a medium with a smaller refractive index. Is it possible, for less than 90°, that the ray within the glass will experience total internal reflection at the glass–air interface? Account for your answer.

| 13 | Suppose you want to make a rainbow by spraying water from a garden hose into the air. (a) Where must you stand relative to the water and the sun to see the rainbow? (b) Why can’t you ever walk under the rainbow?

| 14 | ssm A person is floating on an air mattress in the middle of a swimming pool. His friend is sitting on the side of the pool. The person on the air mattress claims that there is a light shining up from the bottom of the pool directly beneath him. His friend insists, however, that she cannot see any light from where she sits on the side. Can both individuals be correct? Give your reasoning.

| 15 | A beam of blue light is propagating in glass. When the light reaches the boundary between the glass and the surrounding air, the beam is totally reflected back into the glass. However, red light with the same angle of incidence is not totally reflected, and some of the light is refracted into the air. Why do these two colors behave differ ently?

| 16 | A beacon in a lighthouse is to produce a parallel beam of light. The beacon consists of a light bulb and a converging lens. Should the bulb be placed outside the focal point, at the focal point, or in side the focal point of the lens? State your reason.

| 17 | Review Conceptual Example 8 as an aid in answering this question. Is it possible that a converging lens (in air) behaves as a diverging lens when surrounded by another medium? Give a reason for your answer.

| 18 | A spherical mirror and a lens are immersed in water. Compared to the way they work in air, which one do you expect will be more affected by the water? Why?

| 19 | A converging lens is used to project a real image onto a screen, as in Figure 26-27b. A piece of black tape is then placed over the upper half of the lens. Will only the lower half of the image be visible on the screen? Justify your answer by drawing rays from various points on the object to the corresponding points on the image.

| 20 | Review Conceptual Example 8 as an aid in answering this question. A converging lens is made from glass whose index of refraction is n. The lens is surrounded by a fluid whose index of refraction is also n. Can this lens still form an image, either real or virtual, of an object? Why?

| 21 | ssm In a TV mystery program, a photographic negative is introduced as evidence in a court trial. The negative shows an image of a house (now burned down) that was the scene of the crime. At the trial the defendant’s acquittal depends on knowing exactly how far above the ground a window was. An expert called by the defense claims that this height can be calculated from only two pieces of information: (1) the measured height on the film, and (2) the focal length of the camera lens. Explain whether the expert is making sense, using the thin-lens and magnification equations to guide your thinking.

| 22 | Two people who wear glasses are camping. One is nearsighted and the other is farsighted. Whose glasses may be useful in starting a fire with the sun’s rays? Give your reasoning.

| 23 | Suppose that a 21-year-old with normal vision (near point = 25 cm) is standing in front of a plane mirror. How close can he stand to the mirror and still see himself in focus? Explain.

| 24 | If we read for a long time, our eyes become “tired.” When this happens, it helps to stop reading and look at a distant object. From the point of view of the ciliary muscle, why does this refresh the eyes?

| 25 | To a swimmer under water, objects look blurred and out of focus. However, when the swimmer wears goggles that keep the water away from the eyes, the objects appear sharp and in focus. Why do goggles improve a swimmer’s underwater vision?

| 26 | The refractive power of the lens of the eye is 15 diopters when surrounded by the aqueous and vitreous humors. If this lens is removed from the eye and surrounded by air, its refractive power increases to about 150 diopters. Why is the refractive power of the lens so much greater outside the eye?

| 27 | The light shining through a full glass of wine forms an irregularly shaped bright spot on the table, but does not do so when the glass is empty. Explain.

| 28 | Jupiter is the largest planet in our solar system. Yet, to the naked eye, it looks smaller than Venus. Why?

| 29 | Try using Concept Simulations 26.3 and 26.4 at to guide your reasoning here. By means of a ray diagram, show that the eyes of a person wearing glasses appear to be (a) smaller when the glasses use diverging lenses to correct for nearsightedness and (b) larger when the glasses use converging lenses to correct for farsightedness.

| 30 | Can a diverging lens be used as a magnifying glass? Justify your answer with a ray diagram.

| 31 | Who benefits more from using a magnifying glass, a person whose near point is located 25 cm away from the eyes or a person whose near point is located 75 cm away from the eyes? Provide a reason for your answer.

| 32 | Two lenses, whose focal lengths are 3 and 45 cm, are used to build a telescope. Which lens should be the objective? Why?

| 33 | Two refracting telescopes have identical eyepieces, although one telescope is twice as long as the other. Which has the greater angular magnification? Provide a reason for your answer.

| 34 | Suppose a well-designed optical instrument is composed of two converging lenses separated by 14 cm. The focal lengths of the lenses are 0.60 and 4.5 cm. Is the instrument a microscope or a telescope? Why?

| 35 | It is often thought that virtual images are somehow less important than real images. To show that this is not true, identify which of the following instruments normally produce final images that are virtual: (a) a projector, (b) a camera, (c) a magnifying glass, (d) eye glasses, (e) a compound microscope, and (f) an astronomical telescope.

| 36 | Why does chromatic aberration occur in lenses, but not in mirrors?

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