The Fire in the EyeYou have certainly seen the reflected

Problem 1P Scanning Confocal Microscopy Although modern microscopes are marvels of optical engineering, their basic design is not too different from the 1665 compound microscope of Robert Hooke. Recently, advances in optics, lasers, and computer technology have made practical a new kind of optical microscope, the scanning confocal microscope. This microscope is capable of taking images of breathtaking clarity. The figure shows the microscope’s basic principle of operation. The left part of the figure shows how the translucent specimen is illuminated by light from a laser. The laser beam is converted to a diverging bundle of rays by suitable optics, reflected off a mirror, then directed through a microscope objective lens to a focus within the sample. The microscope objective focuses the laser beam to a very small (?0.5 ?m) spot. Note that light from the laser passes through other regions of the specimen but, because the rays are not focused in those regions, they are not as intensely illuminated as is the point at the focus. This is the first important aspect of the design: Very intensely illuminate one very small volume of the sample while leaving other regions only weakly illuminated. As shown in the right half of the figure, light is reflected from all illuminated points in the sample and passes back through the objective lens. The mirror that had reflected the laser light downward is actually a partially transparent mirror that reflects 50% of the light and transmits 50%. Thus half of the light reflected upward from the sample passes through the mirror and is focused on a screen containing a small hole. Because of the hole, only light rays that emanate from the brightly illuminated volume in the sample can completely pass through the hole and reach the light detector behind it. Rays from other points in the sample either miss the hole completely or are out of focus when they reach the screen, so that only a small fraction of them pass through the hole. This second key design aspect limits the detected light to only those rays that are emitted from the point in the sample at which the laser light was originally focused. So we see that (a) the point in the sample that is at the focus of the objective is much more intensely illuminated than any other point, so it reflects more rays than any other point, and (b) the hole serves to further limit the detected rays to only those that emanate from the focus. Taken together, these design aspects ensure the detected light comes from a very small, very well-defined volume in the sample. The microscope as shown would only be useful for examining one small point in the sample. To make an actual image, the objective is scanned across the sample while the intensity is recorded by a computer. This procedure builds up an image of the sample one scan line at a time. The final result is a picture of the sample in the very narrow plane in which the laser beam is focused. Different planes within the sample can be imaged by moving the objective up or down before scanning. It is actually possible to make three dimensional images of a specimen in this way. The improvement in contrast and resolution over conventional microscopy can be striking. The images show a section of a mouse kidney taken using conventional and confocal microscopy. Because light reflected from all parts of the specimen reaches the camera in a conventional microscope, that image appears blurred and has low contrast. The confocal microscope image represents a single plane or slice of the sample, and many details become apparent that are invisible in the conventional image. The following questions are related to the passage “Scanning Confocal Microscopy”. A laser beam consists of parallel rays of light. To convert this light to the diverging rays required for a scanning confocal microscope requires A. A converging lens. B. A diverging lens. C. Either a converging or a diverging lens.

Problem 2P Scanning Confocal Microscopy Although modern microscopes are marvels of optical engineering, their basic design is not too different from the 1665 compound microscope of Robert Hooke. Recently, advances in optics, lasers, and computer technology have made practical a new kind of optical microscope, the scanning confocal microscope. This microscope is capable of taking images of breathtaking clarity. The figure shows the microscope’s basic principle of operation. The left part of the figure shows how the translucent specimen is illuminated by light from a laser. The laser beam is converted to a diverging bundle of rays by suitable optics, reflected off a mirror, then directed through a microscope objective lens to a focus within the sample. The microscope objective focuses the laser beam to a very small (?0.5 ?m) spot. Note that light from the laser passes through other regions of the specimen but, because the rays are not focused in those regions, they are not as intensely illuminated as is the point at the focus. This is the first important aspect of the design: Very intensely illuminate one very small volume of the sample while leaving other regions only weakly illuminated. As shown in the right half of the figure, light is reflected from all illuminated points in the sample and passes back through the objective lens. The mirror that had reflected the laser light downward is actually a partially transparent mirror that reflects 50% of the light and transmits 50%. Thus half of the light reflected upward from the sample passes through the mirror and is focused on a screen containing a small hole. Because of the hole, only light rays that emanate from the brightly illuminated volume in the sample can completely pass through the hole and reach the light detector behind it. Rays from other points in the sample either miss the hole completely or are out of focus when they reach the screen, so that only a small fraction of them pass through the hole. This second key design aspect limits the detected light to only those rays that are emitted from the point in the sample at which the laser light was originally focused. So we see that (a) the point in the sample that is at the focus of the objective is much more intensely illuminated than any other point, so it reflects more rays than any other point, and (b) the hole serves to further limit the detected rays to only those that emanate from the focus. Taken together, these design aspects ensure the detected light comes from a very small, very well-defined volume in the sample. The microscope as shown would only be useful for examining one small point in the sample. To make an actual image, the objective is scanned across the sample while the intensity is recorded by a computer. This procedure builds up an image of the sample one scan line at a time. The final result is a picture of the sample in the very narrow plane in which the laser beam is focused. Different planes within the sample can be imaged by moving the objective up or down before scanning. It is actually possible to make three dimensional images of a specimen in this way. The improvement in contrast and resolution over conventional microscopy can be striking. The images show a section of a mouse kidney taken using conventional and confocal microscopy. Because light reflected from all parts of the specimen reaches the camera in a conventional microscope, that image appears blurred and has low contrast. The confocal microscope image represents a single plane or slice of the sample, and many details become apparent that are invisible in the conventional image. The following questions are related to the passage “Scanning Confocal Microscopy”. If, because of a poor-quality objective, the light from the laser illuminating the sample in a scanning confocal microscope is focused to a larger spot, A. The image would be dimmer because the light illuminating the point imaged would be dimmer. B. The image would be blurry because light from more than one point would reach the detector. C. The image would be dimmer and blurry—both of the above problems would exist.

Problem 3P Scanning Confocal Microscopy Although modern microscopes are marvels of optical engineering, their basic design is not too different from the 1665 compound microscope of Robert Hooke. Recently, advances in optics, lasers, and computer technology have made practical a new kind of optical microscope, the scanning confocal microscope. This microscope is capable of taking images of breathtaking clarity. The figure shows the microscope’s basic principle of operation. The left part of the figure shows how the translucent specimen is illuminated by light from a laser. The laser beam is converted to a diverging bundle of rays by suitable optics, reflected off a mirror, then directed through a microscope objective lens to a focus within the sample. The microscope objective focuses the laser beam to a very small (?0.5 ?m) spot. Note that light from the laser passes through other regions of the specimen but, because the rays are not focused in those regions, they are not as intensely illuminated as is the point at the focus. This is the first important aspect of the design: Very intensely illuminate one very small volume of the sample while leaving other regions only weakly illuminated. As shown in the right half of the figure, light is reflected from all illuminated points in the sample and passes back through the objective lens. The mirror that had reflected the laser light downward is actually a partially transparent mirror that reflects 50% of the light and transmits 50%. Thus half of the light reflected upward from the sample passes through the mirror and is focused on a screen containing a small hole. Because of the hole, only light rays that emanate from the brightly illuminated volume in the sample can completely pass through the hole and reach the light detector behind it. Rays from other points in the sample either miss the hole completely or are out of focus when they reach the screen, so that only a small fraction of them pass through the hole. This second key design aspect limits the detected light to only those rays that are emitted from the point in the sample at which the laser light was originally focused. So we see that (a) the point in the sample that is at the focus of the objective is much more intensely illuminated than any other point, so it reflects more rays than any other point, and (b) the hole serves to further limit the detected rays to only those that emanate from the focus. Taken together, these design aspects ensure the detected light comes from a very small, very well-defined volume in the sample. The microscope as shown would only be useful for examining one small point in the sample. To make an actual image, the objective is scanned across the sample while the intensity is recorded by a computer. This procedure builds up an image of the sample one scan line at a time. The final result is a picture of the sample in the very narrow plane in which the laser beam is focused. Different planes within the sample can be imaged by moving the objective up or down before scanning. It is actually possible to make three dimensional images of a specimen in this way. The improvement in contrast and resolution over conventional microscopy can be striking. The images show a section of a mouse kidney taken using conventional and confocal microscopy. Because light reflected from all parts of the specimen reaches the camera in a conventional microscope, that image appears blurred and has low contrast. The confocal microscope image represents a single plane or slice of the sample, and many details become apparent that are invisible in the conventional image. The following questions are related to the passage “Scanning Confocal Microscopy”. The resolution of a scanning confocal microscope is limited by diffraction, just as for a regular microscope. In principle, switching to a laser with a shorter wavelength would provide A. Greater resolution. B. Lesser resolution. C. The same resolution.

Problem 4P Scanning Confocal Microscopy Although modern microscopes are marvels of optical engineering, their basic design is not too different from the 1665 compound microscope of Robert Hooke. Recently, advances in optics, lasers, and computer technology have made practical a new kind of optical microscope, the scanning confocal microscope. This microscope is capable of taking images of breathtaking clarity. The figure shows the microscope’s basic principle of operation. The left part of the figure shows how the translucent specimen is illuminated by light from a laser. The laser beam is converted to a diverging bundle of rays by suitable optics, reflected off a mirror, then directed through a microscope objective lens to a focus within the sample. The microscope objective focuses the laser beam to a very small (?0.5 ?m) spot. Note that light from the laser passes through other regions of the specimen but, because the rays are not focused in those regions, they are not as intensely illuminated as is the point at the focus. This is the first important aspect of the design: Very intensely illuminate one very small volume of the sample while leaving other regions only weakly illuminated. As shown in the right half of the figure, light is reflected from all illuminated points in the sample and passes back through the objective lens. The mirror that had reflected the laser light downward is actually a partially transparent mirror that reflects 50% of the light and transmits 50%. Thus half of the light reflected upward from the sample passes through the mirror and is focused on a screen containing a small hole. Because of the hole, only light rays that emanate from the brightly illuminated volume in the sample can completely pass through the hole and reach the light detector behind it. Rays from other points in the sample either miss the hole completely or are out of focus when they reach the screen, so that only a small fraction of them pass through the hole. This second key design aspect limits the detected light to only those rays that are emitted from the point in the sample at which the laser light was originally focused. So we see that (a) the point in the sample that is at the focus of the objective is much more intensely illuminated than any other point, so it reflects more rays than any other point, and (b) the hole serves to further limit the detected rays to only those that emanate from the focus. Taken together, these design aspects ensure the detected light comes from a very small, very well-defined volume in the sample. The microscope as shown would only be useful for examining one small point in the sample. To make an actual image, the objective is scanned across the sample while the intensity is recorded by a computer. This procedure builds up an image of the sample one scan line at a time. The final result is a picture of the sample in the very narrow plane in which the laser beam is focused. Different planes within the sample can be imaged by moving the objective up or down before scanning. It is actually possible to make three dimensional images of a specimen in this way. The improvement in contrast and resolution over conventional microscopy can be striking. The images show a section of a mouse kidney taken using conventional and confocal microscopy. Because light reflected from all parts of the specimen reaches the camera in a conventional microscope, that image appears blurred and has low contrast. The confocal microscope image represents a single plane or slice of the sample, and many details become apparent that are invisible in the conventional image. The following questions are related to the passage “Scanning Confocal Microscopy”. In the optical system shown in the passage, the distance from the source of the diverging light rays to the sample is _______ the distance from the sample to the screen. A. greater than B. the same as C. less than

Problem 5P Horse Sense The ciliary muscles in a horse’s eye can make only small changes to the shape of the lens, so a horse can’t change the shape of the lens to focus on objects at different distances as humans do. Instead, a horse relies on the fact that its eyes aren’t spherical. As Figure V.1 shows, different points at the back of the eye are at somewhat different distances from the front of the eye. We say that the eye has a “ramped retina”; images that form on the top of the retina are farther from the cornea and lens than those that form at lower positions. The horse uses this ramped retina to focus on objects at different distances, tipping its head so that light from an object forms an image at a vertical location on the retina that is at the correct distance for sharp focus. In a horse’s eye, the image of a close object will be in focus A. At the top of the retina. B. At the bottom of the retina.

Problem 6P Horse Sense The ciliary muscles in a horse’s eye can make only small changes to the shape of the lens, so a horse can’t change the shape of the lens to focus on objects at different distances as humans do. Instead, a horse relies on the fact that its eyes aren’t spherical. As Figure V.1 shows, different points at the back of the eye are at somewhat different distances from the front of the eye. We say that the eye has a “ramped retina”; images that form on the top of the retina are farther from the cornea and lens than those that form at lower positions. The horse uses this ramped retina to focus on objects at different distances, tipping its head so that light from an object forms an image at a vertical location on the retina that is at the correct distance for sharp focus. In a horse’s eye, the image of a distant object will be in focus A. At the top of the retina. B. At the bottom of the retina.

Problem 7P Horse Sense The ciliary muscles in a horse’s eye can make only small changes to the shape of the lens, so a horse can’t change the shape of the lens to focus on objects at different distances as humans do. Instead, a horse relies on the fact that its eyes aren’t spherical. As Figure V.1 shows, different points at the back of the eye are at somewhat different distances from the front of the eye. We say that the eye has a “ramped retina”; images that form on the top of the retina are farther from the cornea and lens than those that form at lower positions. The horse uses this ramped retina to focus on objects at different distances, tipping its head so that light from an object forms an image at a vertical location on the retina that is at the correct distance for sharp focus. A horse is looking straight ahead at a person who is standing quite close. The image of the person spans much of the vertical extent of the retina. What can we say about the image on the retina? A. The person’s head is in focus; the feet are out of focus. B. The person’s feet are in focus; the head is out of focus. C. The person’s head and feet are both in focus. D. The person’s head and feet are both out of focus.

Problem 8P Horse Sense The ciliary muscles in a horse’s eye can make only small changes to the shape of the lens, so a horse can’t change the shape of the lens to focus on objects at different distances as humans do. Instead, a horse relies on the fact that its eyes aren’t spherical. As Figure V.1 shows, different points at the back of the eye are at somewhat different distances from the front of the eye. We say that the eye has a “ramped retina”; images that form on the top of the retina are farther from the cornea and lens than those that form at lower positions. The horse uses this ramped retina to focus on objects at different distances, tipping its head so that light from an object forms an image at a vertical location on the retina that is at the correct distance for sharp focus. Certain medical conditions can change the shape of a horse’s eyeball; these changes can affect vision. If the lens and cornea are not changed but all of the distances in Figure V.1 are increased slightly, then the horse will be A. Nearsighted. B. Farsighted. C. Unable to focus clearly at any distance.

Problem 9P The Fire in the Eye You have certainly seen the reflected light from the eyes of a cat or a dog at night. This “eye shine” is the reflection of light from a layer at the back of the eye called the tapetum lucidum (Latin for “bright carpet”). The tapetum is a common structure in the eyes of animals that must see in low light. Light that passes through the retina is reflected by the tapetum back through the cells of the retina, giving them a second chance to detect the light. Sharks and related fish have a very well-developed tapetum. Figure V.2 a shows a camera flash reflected from a shark’s eye back toward the camera. This reflected light is much brighter than the diffuse reflection from the body of the shark. How is this bright reflection created? Figure V.2 b shows a typical tapetum structure for a fish. (The tapetum in land animals such as cats, dogs, and deer uses similar principles but has a different structure.) The reflection comes from the interfaces between two layers of nearly transparent cells (whose index of refraction is essentially that of water) and a stack of guanine crystals sandwiched between. Light is reflected from the interface at both sides of the stack of crystals. For certain wavelengths, constructive interference leads to an especially strong reflection. Bright light from a distant source is focused by the lens of a shark’s eye to a point on the retina, as shown in Figure V.2 c. The tapetum reflects these rays back through the lens, where refraction bends them into parallel rays traveling back toward the source of the light. Because the reflected light from the tapetum is directional, it is much brighter than the diffuse reflection from the shark’s body. But the bright reflection is seen by an observer—or a camera—only at or near the source of the flash that produced the reflection. Light of wavelength 600 nm in air passes into the layer of guanine crystals. What is the wavelength of the light in this layer? A. 1100 nm B. 600 nm C. 450 nm D. 330 nm

Problem 10P The Fire in the Eye You have certainly seen the reflected light from the eyes of a cat or a dog at night. This “eye shine” is the reflection of light from a layer at the back of the eye called the tapetum lucidum (Latin for “bright carpet”). The tapetum is a common structure in the eyes of animals that must see in low light. Light that passes through the retina is reflected by the tapetum back through the cells of the retina, giving them a second chance to detect the light. Sharks and related fish have a very well-developed tapetum. Figure V.2 a shows a camera flash reflected from a shark’s eye back toward the camera. This reflected light is much brighter than the diffuse reflection from the body of the shark. How is this bright reflection created? Figure V.2 b shows a typical tapetum structure for a fish. (The tapetum in land animals such as cats, dogs, and deer uses similar principles but has a different structure.) The reflection comes from the interfaces between two layers of nearly transparent cells (whose index of refraction is essentially that of water) and a stack of guanine crystals sandwiched between. Light is reflected from the interface at both sides of the stack of crystals. For certain wavelengths, constructive interference leads to an especially strong reflection. Bright light from a distant source is focused by the lens of a shark’s eye to a point on the retina, as shown in Figure V.2 c. The tapetum reflects these rays back through the lens, where refraction bends them into parallel rays traveling back toward the source of the light. Because the reflected light from the tapetum is directional, it is much brighter than the diffuse reflection from the shark’s body. But the bright reflection is seen by an observer—or a camera—only at or near the source of the flash that produced the reflection. Figure V.2 b shows rays that reflect from the two interfaces in the tapetum. Given the indices of refraction of the cells and the crystals, there will be a phase shift on reflection for A. The front reflection and the rear reflection. B. The front reflection only. C. The rear reflection only. D. Neither the front nor the rear reflection.

Problem 11P The Fire in the Eye You have certainly seen the reflected light from the eyes of a cat or a dog at night. This “eye shine” is the reflection of light from a layer at the back of the eye called the tapetum lucidum (Latin for “bright carpet”). The tapetum is a common structure in the eyes of animals that must see in low light. Light that passes through the retina is reflected by the tapetum back through the cells of the retina, giving them a second chance to detect the light. Sharks and related fish have a very well-developed tapetum. Figure V.2 a shows a camera flash reflected from a shark’s eye back toward the camera. This reflected light is much brighter than the diffuse reflection from the body of the shark. How is this bright reflection created? Figure V.2 b shows a typical tapetum structure for a fish. (The tapetum in land animals such as cats, dogs, and deer uses similar principles but has a different structure.) The reflection comes from the interfaces between two layers of nearly transparent cells (whose index of refraction is essentially that of water) and a stack of guanine crystals sandwiched between. Light is reflected from the interface at both sides of the stack of crystals. For certain wavelengths, constructive interference leads to an especially strong reflection. Bright light from a distant source is focused by the lens of a shark’s eye to a point on the retina, as shown in Figure V.2 c. The tapetum reflects these rays back through the lens, where refraction bends them into parallel rays traveling back toward the source of the light. Because the reflected light from the tapetum is directional, it is much brighter than the diffuse reflection from the shark’s body. But the bright reflection is seen by an observer—or a camera—only at or near the source of the flash that produced the reflection. What is the (approximate) smallest thickness of the crystal layer that would lead to constructive interference between the front reflection and the rear reflection for light of wavelength 600 nm?

Problem 12P The Fire in the Eye You have certainly seen the reflected light from the eyes of a cat or a dog at night. This “eye shine” is the reflection of light from a layer at the back of the eye called the tapetum lucidum (Latin for “bright carpet”). The tapetum is a common structure in the eyes of animals that must see in low light. Light that passes through the retina is reflected by the tapetum back through the cells of the retina, giving them a second chance to detect the light. Sharks and related fish have a very well-developed tapetum. Figure V.2 a shows a camera flash reflected from a shark’s eye back toward the camera. This reflected light is much brighter than the diffuse reflection from the body of the shark. How is this bright reflection created? Figure V.2 b shows a typical tapetum structure for a fish. (The tapetum in land animals such as cats, dogs, and deer uses similar principles but has a different structure.) The reflection comes from the interfaces between two layers of nearly transparent cells (whose index of refraction is essentially that of water) and a stack of guanine crystals sandwiched between. Light is reflected from the interface at both sides of the stack of crystals. For certain wavelengths, constructive interference leads to an especially strong reflection. Bright light from a distant source is focused by the lens of a shark’s eye to a point on the retina, as shown in Figure V.2 c. The tapetum reflects these rays back through the lens, where refraction bends them into parallel rays traveling back toward the source of the light. Because the reflected light from the tapetum is directional, it is much brighter than the diffuse reflection from the shark’s body. But the bright reflection is seen by an observer—or a camera—only at or near the source of the flash that produced the reflection. In human vision, the curvature of the cornea provides much of the power of the visual system. This is not the case in fish; in Figure V.2 c, the light rays are bent by the lens but are not bent when they enter the cornea. This is because A. Fish eyes work in water, and the index of refraction of the fluids in the eye is similar to that of water. B. Fish eyes have a much smaller curvature of the cornea. C. Most fish have eyes that are more sensitive to light than the eyes of typical land animals. D. The reflection of the tapetum interferes with the refraction of the cornea.

Problem 13P The Fire in the Eye You have certainly seen the reflected light from the eyes of a cat or a dog at night. This “eye shine” is the reflection of light from a layer at the back of the eye called the tapetum lucidum (Latin for “bright carpet”). The tapetum is a common structure in the eyes of animals that must see in low light. Light that passes through the retina is reflected by the tapetum back through the cells of the retina, giving them a second chance to detect the light. Sharks and related fish have a very well-developed tapetum. Figure V.2 a shows a camera flash reflected from a shark’s eye back toward the camera. This reflected light is much brighter than the diffuse reflection from the body of the shark. How is this bright reflection created? Figure V.2 b shows a typical tapetum structure for a fish. (The tapetum in land animals such as cats, dogs, and deer uses similar principles but has a different structure.) The reflection comes from the interfaces between two layers of nearly transparent cells (whose index of refraction is essentially that of water) and a stack of guanine crystals sandwiched between. Light is reflected from the interface at both sides of the stack of crystals. For certain wavelengths, constructive interference leads to an especially strong reflection. Bright light from a distant source is focused by the lens of a shark’s eye to a point on the retina, as shown in Figure V.2 c. The tapetum reflects these rays back through the lens, where refraction bends them into parallel rays traveling back toward the source of the light. Because the reflected light from the tapetum is directional, it is much brighter than the diffuse reflection from the shark’s body. But the bright reflection is seen by an observer—or a camera—only at or near the source of the flash that produced the reflection. Flash photographs of cats will generally show the tapetum reflection unless you are careful to avoid it. If you want to take a flash photograph of your cat while minimizing the “eye shine,” which of the following strategies will not work? A. Take the photographs in dim light so that the irises of your cat’s eyes are wide open. B. Use a flash on a stand at some distance from the camera. C. Use a diffuser so that the light from the flash is spread over a wide area. D. Use multiple flashes at different positions around the room.

Problem 14P The Fire in the Eye You have certainly seen the reflected light from the eyes of a cat or a dog at night. This “eye shine” is the reflection of light from a layer at the back of the eye called the tapetum lucidum (Latin for “bright carpet”). The tapetum is a common structure in the eyes of animals that must see in low light. Light that passes through the retina is reflected by the tapetum back through the cells of the retina, giving them a second chance to detect the light. Sharks and related fish have a very well-developed tapetum. Figure V.2 a shows a camera flash reflected from a shark’s eye back toward the camera. This reflected light is much brighter than the diffuse reflection from the body of the shark. How is this bright reflection created? Figure V.2 b shows a typical tapetum structure for a fish. (The tapetum in land animals such as cats, dogs, and deer uses similar principles but has a different structure.) The reflection comes from the interfaces between two layers of nearly transparent cells (whose index of refraction is essentially that of water) and a stack of guanine crystals sandwiched between. Light is reflected from the interface at both sides of the stack of crystals. For certain wavelengths, constructive interference leads to an especially strong reflection. Bright light from a distant source is focused by the lens of a shark’s eye to a point on the retina, as shown in Figure V.2 c. The tapetum reflects these rays back through the lens, where refraction bends them into parallel rays traveling back toward the source of the light. Because the reflected light from the tapetum is directional, it is much brighter than the diffuse reflection from the shark’s body. But the bright reflection is seen by an observer—or a camera—only at or near the source of the flash that produced the reflection. Figure V.2 c shows the lens of the eye bringing parallel rays together right at the retina. The retina is located A. In front of the focal point of the lens. B. At the focal point of the lens. C. Behind the focal point of the lens.

Problem 15AIP The pupil of your eye is smaller in bright light than in dim light. Explain how this makes images seen in bright light appear sharper than images seen in dim light.

Problem 16AIP People with good vision can make out an 8.8-mm-tall letter on an eye chart at a distance of 6.1 m. Approximately how large is the image of the letter on the retina? Assume that the distance from the lens to the retina is 24 mm.

Problem 17AIP A photographer uses a lens with f = 50 mm to form an image of a distant object on the CCD detector in a digital camera. The image is 1.2 mm high, and the intensity of light on the detector is . She then switches to a lens with f = 300 mm that is the same diameter as the first lens. What are the height of the image and the intensity now?

Problem 18AIP Sound and other waves undergo diffraction just as light does. Suppose a loudspeaker in a 20°C room is emitting a steady tone of 1200 Hz. A 1.0-m-wide doorway in front of the speaker diffracts the sound wave. A person on the other side walks parallel to the wall in which the door is set, staying 12 m from the wall. When he is directly in front of the doorway, he can hear the sound clearly and loudly. As he continues walking, the sound intensity decreases. How far must he walk from the point where he was directly in front of the door until he reaches the first quiet spot?