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physics
college physics 2nd

College Physics A Strategic Approach 4th Edition Randall D. Knight, Brian Jones - Solutions

In a fish tank, it is possible to have stray potentials from lights and other equipment. The fish in the tank position themselves to minimize the potential difference between any two points on their bodies. Suppose there is a dipole field in a fish tank resulting from the charges shown in the top
Figure Q21.21 shows two concentric circular electrodes, charged as noted. What can you conclude about the electric potential and the field strength at the two noted points between the two electrodes?A. The potential is greater at point A; the field strength is greater at pointA. B. The potential
The radius of a calcium atom is approximately 0.23 nm. What is the ionization energy?
The radius of a cadmium atom is approximately 0.16 nm. What is the ionization energy?
Guiana dolphins are one of the few mammals able to detect electric fields. In a test of sensitivity, a dolphin was exposed to the variable electric field from a pair of charged electrodes. The magnitude of the electric field near the sensory organs was measured by detecting the potential difference
Raindrops acquire an electric charge as they fall. Suppose a 2.5-mm-diameter drop has a charge of +15 pC, fairly typical values. What is the potential at the surface of the raindrop?
Students in an introductory physics lab are producing a region of uniform electric field by applying a voltage to two 20-cmdiameter aluminum plates separated by 2.5 cm. They connect the two plates to the two terminals of a high-voltage power supply and then gradually turn up the voltage. In such a
In experimental tests, sharks have shown the ability to locate dipole electrodes (simulating the dipole fields of the heartbeats of prey animals) buried under the sand. In a test with young bonnethead sharks, sharks that detected the presence of a dipole usually swam toward the center of the dipole
The gecko in the photo is sticking upside down to a smooth ceiling. The remarkable adhesion might be due to static electricity. Gecko feet are covered with microscopic hairs. When these hairs rub against a surface, charges separate, with the hair developing a positive charge and negative charge
When a hummingbird visits a flower, its wings rub against the flower and leaves, and this can result in a noticeable charge on the bird. There is an opposite charge in the earth. We can consider the hummingbird and the earth to be the two electrodes of a capacitor. The capacitance for one species
The earth is negatively charged, carrying 500,000 C of electric charge. This results in a 300 kV potential difference between the earth and the positively charged ionosphere. What is the capacitance of the earth–ionosphere system? If we assume that the bottom of the ionosphere is 60 km above the
Nerve cells in your body can be electrically stimulated; a large enough change in a membrane potential triggers a nerve impulse. Certain plants work the same way. A touch to mimosa pudica, the “sensitive plant,” causes the leaflets to fold inward and droop. We can trigger this response
Investigators are exploring ways to treat milk for longer shelf life by using pulsed electric fields to destroy bacterial contamination. One system uses 8.0-cm-diameter circular plates separated by 0.95 cm. The space between the plates is filled with milk, which has a dielectric constant the same
We’ve seen that bees develop a positive charge as they fly through the air. When a bee lands on a flower, charge is transferred, and an opposite charge is induced in the earth below the flower. The flower and the ground together make a capacitor; a typical value is 0.80 pF. If a flower is charged
A proton follows the path shown in Figure P21.74. Its initial speed is v0 = 1.9 × 106 m/s. What is the proton’s speed as it passes through point P? 4.0 mm P -10 nC FIGURE P21.74 3.0 mm
DVDs and Blu-ray disks store information in patterns that are read by laser light. The shorter the wavelength of the light, the closer the data tracks can be placed on the disk. A Blu-ray player uses violet light; a DVD player uses red light. Which disk can store more information?
Increasing the density of a material tends to increase the index of refraction. Does light travel faster in seawater or in fresh water?
If you look at the light spectrum reflected from the surface of a DVD compared to the spectrum reflected from the surface of a CD, you’ll see that the rainbows from the DVD are more spread out, with greater angular separation. What does this tell you about the relative track spacing on these two
If you look through a piece of very fine fabric at a tiny white light source, you will see a rainbow pattern. Explain the source of the pattern.
Antireflection coatings for glass usually have an index of refraction that is less than that of glass. Explain how this permits a thinner coating.
Solar cells generally have an antireflection coating. Explain how this increases their efficiency.
The distinctly blue shade of a blue spruce results from the scattering of light by small waxy particles that coat the leaves. Explain how this scattering can protect the leaves from damage by short-wavelength ultraviolet light while still permitting the passage of longer wavelengths of light for
An investigator is using a laser to illuminate a distant target. He decides that he needs a smaller beam, so he puts a pinhole directly in front of the laser. He finds that this actually spreads the beam out, making matters worse. Explain what is happening.
Data are carried by pulses of light through long, transparent fibers—fiber-optic cables. Long lengths of fiber carry signals 100 km between amplifier stations. How long does it take a signal to travel this distance if the index of refraction of the fiber is 1.45?
A commercial diffraction grating has 500 lines per mm. When a student shines a 530 nm laser through this grating, how many bright spots could be seen on a screen behind the grating?
A physics instructor wants to project a spectrum of visible light colors from 400 nm to 700 nm as part of a classroom demonstration. She shines a beam of white light through a diffraction grating that has 500 lines per mm, projecting a pattern on a screen 2.4 m behind the grating.a. How wide is
Figure P17.22 shows a microscopic view of muscle tissue. In the figure, structures called sarcomeres are bordered by ridges. The regular pattern of the ridges means that the muscle can operate as a reflection grating, and a measurement of the resulting diffraction pattern can give a measurement
Pigments don’t survive fossilization; even though we have fossil skin from dinosaurs, we don’t know what color they were. But fossilization does preserve structure. Specimens from a rare cache of 50-million-year-old beetle fossils still show the microscopic layers that produced structural
Mourning doves have a small patch of iridescent feathers. The color is produced by a 330-nmthick layer of keratin (n = 1.562 with air on both sides that is found around the edge of the feather barbules. For what wavelength or wavelengths would this structure produce constructive interference?
Early investigators (including Thomas Young) measured the thickness of wool fibers using diffraction. One early instrument used a collimated beam of 560 nm light to produce a diffraction pattern on a screen placed 30 cm from a single wool fiber. If the fiber’s diameter was 16 μm, what was the
Quality control systems have been developed to remotely measure the diameter of wires using diffraction. A wire with a stated diameter of 170 mm blocks the beam of a 633 nm laser, producing a diffraction pattern on a screen 50.0 cm distant. The width of the central maximum is measured to be 3.77
Diffraction can be used to provide a quick test of the size of red blood cells. Blood is smeared onto a slide, and a laser shines through the slide. The size of the cells is very consistent, so the multiple diffraction patterns overlap and produce an overall pattern that is similar to what a single
On the earth, you can see the ground in someone’s shadow; on the moon, you can’t—the shadow is deep black. Explain the difference.
On a day with fresh snow, you might notice that shadows— where the direct light from the sun is blocked—have a distinctly bluish cast. Explain why you might expect this.
The light spots that form a circle around the outside of the fountain in Figure Q18.8 come from a light source in the center of the fountain. Explain how the light makes it from the center of the fountain to the circles of light on the ground where the water hits. FIGURE Q18.8
If you hold a spoon in front of your face so that you see your image in the bowl of the spoon, your image is upright when you hold the spoon close to your face, but inverted when you hold the spoon far away. Explain why this change occurs.
Figure Q18.15 shows a photograph of droplets of water suspended from the stem of a plant in a garden, with a flower behind. There appear to be small flowers in each of the droplets; explain what is happening here. FIGURE Q18.15
Figure Q18.16 shows droplets of water beaded up on a leaf. The light is coming from the left. The droplets work like a lens, focusing sunlight to bright spots behind the droplets. Use the ray model of light to explain why each bright spot is surrounded by a dark ring. FIGURE Q18.16
In Figure P18.2, the compact flame of a candle casts a 15-cm-high shadow of a 8.2-cm-tall tree cutout. The candle is 3.2 cm from the cutout; how far is the candle from the wall? FIGURE P18.2
The lightbulb in Figure P18.10 is 50 cm from a mirror. It emits 1.5 W of visible light. A small barrier blocks the direct rays of light from the bulb from reaching a sensor 70 cm to the right, but not the reflected rays. What is the light intensity at the sensor? 50 cm Mirror Sensor Barrier Bulb 70
The sun is 60° above the horizon. Rays from the sun strike the still surface of a pond and cast a shadow of a stick that is stuck in the sandy bottom of the pond. If the stick is 10 cm tall, how long is the shadow?
Figure P18.16 shows a ray of light entering an equilateral prism, with all sides and angles equal to each other. The ray traverses the prism parallel to the bottom and emerges at the same angle at which it entered. If u = 40°, what is the index of refraction of the prism? FIGURE P18.16
You are on a snorkeling trip. Deep below the water, you look up at the surface of the water. Right at sunset, at what angle from the vertical do you see the sun?
A typical diamond is cut as shown in Figure P18.22. A ray of light has entered the flat window at the top of the diamond perpendicular to the surface, as shown in the figure. Analyze the path of the ray for the next two interactions with the surfaces of the diamond. FIGURE P18.22 41
In order to start a fire, a camper turns a lens toward the sun to focus its rays on a piece of wood. The lens has a 10 cm focal length. Draw a ray diagram of the lens and the incoming light rays to show where the wood should be placed for the best effect.
You are using a converging lens to look at a splinter in your finger. The lens has a 9.0 cm focal length, and you place the splinter 6.0 cm from the lens. How far from the lens is the image? What is the magnification?
A photographer took this image of himself in a converging mirror. Give some thought to what you are seeing here: One of the hands is his left hand; the other is the image of his left hand. Given the relative sizes and positions of his hand and the image of his hand, how far from the mirror did he
A flashlight uses a small lightbulb placed in front of a converging mirror. The light from the bulb should reflect from the mirror and emerge as a tight beam of light—a series of parallel rays. Where should the bulb be placed relative to the mirror?
The sun is 150,000,000 km from earth; its diameter is 1,400,000 km. A student uses a 4.0-cm-diameter lens with f = 10 cm to cast an image of the sun on a piece of paper. a. Where should the paper be placed to get a sharp image? b. What is the diameter of the image on the paper? c. The intensity of
The sun is 150,000,000 km from earth; its diameter is 1,400,000 km. For a science project on solar power, a student uses a 24-cm-diameter converging mirror with a focal length of 45 cm to focus sunlight onto an object. This casts an image of the sun on the object. For the most intense heat, the
Consider a typical diverging passenger-side mirror with a focal length of -80 cm. A 1.5-m-tall cyclist on a bicycle is 25 m from the mirror. You are 1.0 m from the mirror, and suppose, for simplicity, that the mirror, you, and the cyclist all lie along a line.a. How far are you from the image of
Figure Q19.3 shows the viewing screen in an English camera obscura, a windowless room with a lens in one wall and a screen on the opposite wall, 3 meters from the lens. What can you say about the focal length of the lens? FIGURE Q19.3
A telephoto lens—designed to produce large images of distant objects—sticks out quite far from the front of the camera. Explain why this is so.
Young children usually have a fair degree of hyperopia. As they grow, their eyeballs lengthen and the hyperopia usually clears up. Given what you know about accommodation, explain why young children, though hyperopic, don’t need glasses.
Children of the Moken tribe spend much of their days foraging for food underwater. Their eyes are adapted to this; their lenses are capable of more accommodation and, when they dive, their pupils contract. Explain how each of these changes improves their underwater vision.
Water that comes from the tap is a good conductor of electricity. In the chapter preview, you can see a photograph that shows a stream of water being attracted to a charged comb.a. Explain why the water stream is attracted to the comb.b. Water droplets that break off from the stream are strongly
When you are painting a car with a sprayer, you get more even coverage (the paint droplets are evenly spread out) and less overspray (fewer droplets of paint that don’t end up on the vehicle) if you give the droplets a strong electric charge.a. Why does charging the droplets give more even
Many drugs under development are delivered by nanoparticles in the bloodstream. To monitor changes in the nanoparticles, investigators can retrieve them from the blood by using a device with electrodes that apply oscillating electric fields. The nanoparticles, which are electrically conducting, are
Home professionals like realtors use ultrasonic measuring tools to quickly measure the size of rooms. These instruments work by sending out a pulse of ultrasonic sound, then measuring the time it takes for this pulse to reflect off a wall and return to the device. If you used such a device on a
When in air, a waterproof speaker emits sound waves that have a frequency of 1000 Hz. When the speaker is lowered into water, does the frequency of the sound increase, decrease, or remain the same? Does the wavelength of the sound increase, decrease, or remain the same?
A wave pulse travels along a horizontal string. As the pulse passes a point on the string, the point moves vertically up and then back down again. How does the vertical speed of the point compare to the speed of the wave?
The probe used in a medical ultrasound examination emits sound waves in air that have a wavelength of 0.12 mm. What is the wavelength of the sound waves in the patient?A. 0.027 mmB. 0.12 mmC. 0.26 mmD. 0.54 mm
Bats sense objects in the dark by echolocation, in which they emit very short pulses of sound and then listen for their echoes off the objects. A bat is flying directly toward a wall 50 m away when it emits a pulse. 0.28 s later it receives the pulse. What is the bat’s speed?
A scientist measures the speed of sound in a monatomic gas to be 449 m/s at 20°C. What element does this gas consist of?
A sinusoidal wave moving to the left has a wavelength of 5.0 cm and a frequency of 50 Hz. At t = 0 s, the wave has a crest at x = 0 cm. What is the earliest time after t = 0 s at which there is a crest at the position x = 3.0 cm?
Elephants can communicate over distances as far as 6 km by using very low-frequency sound waves. What is the wavelength of a 10 Hz sound wave emitted by an elephant?
A bullet shot from a rifle travels at 1000 m/s. What is the elapsed time between when the bullet strikes a target 500 m away, and when the sound of the gunshot reaches the target?
A sun-like star is barely visible to naked-eye observers on earth when it is a distance of 7.0 light years, or 6.6 × 1016 m, away. The sun emits a power of 3.8 × 1026 W. Using this information, at what distance would a candle that emits a power of 0.20 W just be visible?
The world’s most powerful laser is the LFEX laser in Japan. It can produce a 2 petawatt 12 × 1015 W2 laser pulse that last for 1 ps. The laser is focused onto a small spot that is 30 μm in diameter. What is the light intensity within this spot?
The record for the world’s loudest burp is 109.9 dB, measured at a distance of 2.5 m from the burper. Assuming that this sound was emitted as a spherical wave, what was the power emitted by the burper during his record burp?
The African cicada is the world’s loudest insect, producing a sound intensity level of 107 dB at a distance of 0.50 m. What is the intensity of its sound (in W/m2) as heard by someone standing 3.0 m away?
From a distance of 4.0 m, a bystander listens to a jackhammer breaking concrete. How far would he need to move from the jackhammer so that its perceived loudness decreases by a factor of 8?
When you speak, your voice sounds 10 dB louder to someone standing directly in front of you than to someone at the same distance but directly behind you. What is the ratio of the intensity of your voice for someone in front of you to the intensity for someone behind you?
At the 18 km cruising altitude of Concorde, a passenger aircraft that flew at twice the speed of sound, the temperature was -57°C. What was the Concorde’s cruising speed?
A small wave pulse and a large wave pulse approach each other on a string; the large pulse is moving to the right. Some time after the pulses have met and passed each other, which of the following statements is correct? (More than one answer may be correct.) Explain.A. The large pulse continues
You are listening to music from a loudspeaker. Then a second speaker is turned on. Is it possible that the music you now hear is quieter than it was with only the first speaker playing? Explain.
If you’re swimming underwater and knock two rocks together, you will hear a very loud noise. But if your friend above the water knocks two rocks together, you’ll barely hear the sound. Explain.
A washtub bass is a simple instrument consisting of a string stretched between a pole and a metal washtub. The musician can play different notes by pulling back more or less on the pole. Explain how this tuning method works.
You are standing directly between two loudspeakers playing identical 350 Hz tones. Describe what you will hear if you start walking along a line perpendicular to the line between the speakers.
Figure Q16.14 shows frequency spectra of the same note played on a flute (modeled as an open-open tube) and on a clarinet (a closed-open tube). Which figure corresponds to the flute, and which to the clarinet? Explain. Intensity A B f(Hz) FIGURE Q16.14 Intensity f(Hz).
The four strings of a bass guitar are 0.865 m long and are tuned to the notes G (98 Hz), D (73.4 Hz), A (55 Hz), and E (41.2 Hz). In one bass guitar, the G and D strings have a linear mass density of 5.8 g/m, and the A and E strings have a linear mass density of 26.8 g/m. What is the total force
The G string on a guitar is 59 cm long and has a fundamental frequency of 196 Hz. A guitarist can play different notes by pushing the string against various frets, which changes the string’s length. The first fret from the neck gives A" (207.65 Hz); the second fret gives A (220 Hz). How far apart
Some guitarists like the feel of a set of strings that all have the same tension. For such a guitar, the G string (196 Hz) has a mass density of 0.31 g/m. What is the mass density of the A string (110 Hz)?
To study the physical basis of underwater hearing in frogs, scientists used a vertical tube filled with water to a depth of 1.4 m. A microphone at the bottom of the tube was used to create standing sound waves in the water column. Frogs were lowered to different depths where the standing waves
The vuvuzela is a simple horn, typically 0.65 m long, that fans use to make noise at sporting events. What is the frequency of the fundamental note produced by a vuvuzela?
The pan flute is a musical instrument consisting of a number of closed-end tubes of different lengths. When the musician blows over the open ends, each tube plays a different note. The longest pipe is 0.33 m long. What is the frequency of the note it plays?
Figure P16.36 shows the two lowest resonances recorded in the vocal tract of the eastern towhee, a small songbird.a. Is this bird’s vocal tract better modeled as an open-open tube or an open-closed tube?b. Estimate the length of the towhee’s vocal tract. Relative intensity 2 3 4 5 6 7 8
Two loudspeakers, 1.0 m apart, emit sound waves with the same frequency along the positive x-axis. Victor, standing on the axis to the right of the speakers, hears no sound. As the frequency is slowly tripled, Victor hears the sound go through the sequence loud-soft-loud-soft-loud before becoming
A guitar player can change the frequency of a string by “bending” it—pushing it along a fret that is perpendicular to its length. This stretches the string, increasing its tension and its frequency. The G string on a guitar is 64 cm long and has a tension of 74 N. The guitarist pushes this
The pendulum on a grandfather clock has a period of 2.00 s. If the clock is not wound, the pendulum’s amplitude begins to decay at a rate of 0.53% each pendulum period.a. What is the time constant of this pendulum?b. What percentage of the pendulum’s energy is lost each period?
A block with a mass of 0.28 kg is attached to a horizontal spring. The block is pulled back from its equilibrium position until the spring exerts a force of 1.0 N on the block. When the block is released, it oscillates with a frequency of 1.2 Hz. How far was the block pulled back before being
The motion of a nightingale’s wingtips can be modeled as simple harmonic motion. In one study, the tips of a bird’s wings were found to move up and down with an amplitude of 8.8 cm and a period of 0.82 s. What are the wingtips’(a) maximum speed(b) maximum acceleration?
In a loudspeaker, an electromagnetic coil rapidly drives a paper cone back and forth, sending out sound waves. If the cone of a loudspeaker moves sinusoidally at 1.2 kHz with an amplitude of 3.5 μm, what are the cone’s maximum speed and acceleration?
In a study designed to better understand the dynamics of walking, a subject stood with one leg at rest, and swung the other leg at various frequencies. The metabolic power expended, in watts per kilogram of body weight, is shown in Figure P14.36. Estimate the length of this subject’s legs. FIGURE
A child on a swing set swings back and forth with a period of 3.3 s and an amplitude of 25°. What is the maximum speed of the child as she swings?
The common field cricket makes its characteristic loud chirping sound using a specialized vibrating structure in its wings. The motion of this structure—and the sound intensity that it produces—can be modeled as a damped oscillation. The sound intensity of such a cricket is shown in Figure
In a science museum, you may have seen a Foucault pendulum, which is used to demonstrate the rotation of the earth. In one museum’s pendulum, the 110 kg bob swings from a 15.8-m-long cable with an amplitude of 5.0°.a. What is the period of this pendulum?b. What is the bob’s maximum
A damped pendulum has a period of 0.66 s and a time constant of 4.1 s. How many oscillations will this pendulum make before its amplitude has decreased to 20% of its initial amplitude?
A circular cylinder has a diameter of 2.0 cm and a mass of 10 g. It floats in water with its long axis perpendicular to the water’s surface. It is pushed down into the water by a small distance and released; it then bobs up and down. What is the oscillation frequency?
Tarzan, who has a mass of 80 kg, holds onto the end of a vine that is at a 12° angle from the vertical. He steps off his branch and, just at the bottom of his swing, he grabs onto his chimp friend Cheetah, whose mass is 40 kg. What is the maximum angle the rope reaches as Tarzan swings to the

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