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physics
college physics 2nd

College Physics 2nd Edition OpenStax - Solutions

Consider an electric immersion heater used to heat a cup of water to make tea. Construct a problem in which you calculate the needed resistance of the heater so that it increases the temperature of the water and cup in a reasonable amount of time. Also calculate the cost of the electrical energy
(a) What is the hot resistance of a 25-W light bulb that runs on 120-V AC? (b) If the bulb's operating temperature is 2700°C, what is its resistance at 2600°C?
Certain heavy industrial equipment uses AC power that has a peak voltage of 679 V. What is the rms voltage?
A certain circuit breaker trips when the rms current is 15.0 A. What is the corresponding peak current?
Military aircraft use 400-Hz AC power, because it is possible to design lighter-weight equipment at this higher frequency. What is the time for one complete cycle of this power?
A North American tourist takes his 25.0-W, 120-V AC razor to Europe, finds a special adapter, and plugs it into 240 V AC. Assuming constant resistance, what power does the razor consume as it is ruined?
A small office-building air conditioner operates on 408-V AC and consumes 50.0 kW. (a) What is its effective resistance? (b) What is the cost of running the air conditioner during a hot summer month when it is on 8.00 h per day for 30 days and electricity costs 9.00 cents/kW.h?
What is the peak current through a 500-W room heater that operates on 120-V AC power?
Two different electrical devices have the same power consumption, but one is meant to be operated on 120-V AC and the other on 240-V AC.(a) What is the ratio of their resistances?(b) What is the ratio of their currents?(c) Assuming its resistance is unaffected, by what factor will the power
Nichrome wire is used in some radiative heaters. (a) Find the resistance needed if the average power output is to be 1.00 kW utilizing 120-V AC.(b) What length of Nichrome wire, having a cross- sectional area of 5.00mm2, is needed if the operating temperature is 500° C? (c) What power will it
(a) At what two times in the first period following t = 0 does the instantaneous voltage in 60-Hz AC equal vrms? (b) - vrms?
(a) How much power is dissipated in a short circuit of 220-V AC through a resistance of 0.250 Ω? (b) What current flows?
What voltage is involved in a 1.44-kW short circuit through a 0.100- Ω resistance?
Find the current through a person and identify the likely effect on her if she touches a 120-V AC source:(a) If she is standing on a rubber mat and offers a total resistance of 300 kΩ; (b) If she is standing barefoot on wet grass and has a resistance of only 4500 Ω.
While taking a bath, a person touches the metal case of a radio. The path through the person to the drainpipe and ground has a resistance of 4000 Ω. What is the smallest voltage on the case of the radio that could cause ventricular fibrillation?
(a) During surgery, a current as small as 20.0 μA applied directly to the heart may cause ventricular fibrillation. If the resistance of the exposed heart is 300 Ω, what is the smallest voltage that poses this danger? (b) Does your answer imply that special electrical safety precautions are
(a) What is the resistance of a 220-V AC short circuit that generates a peak power of 96.8 kW?(b) What would the average power be if the voltage was 120 V AC?
A heart defibrillator passes 10.0 A through a patient’s torso for 5.00 ms in an attempt to restore normal beating. (a) How much charge passed? (b) What voltage was applied if 500 J of energy was dissipated?(c) What was the path’s resistance?(d) Find the temperature increase caused in the 8.00
A short circuit in a 120-V appliance cord has a 0.500-Ω resistance. Calculate the temperature rise of the 2.00 g of surrounding materials, assuming their specific heat capacity is 0.200 cal/g. °C and that it takes 0.0500 s for a circuit breaker to interrupt the current. Is this likely to be
Use the ECG in Figure 20.31 to determine the heart rate in beats per minute assuming a constant time between beats.Data given in Figure 20.31 Arterial blood pressure (mm Hg) Lead Il voltage (m V) 120 100 1.0 0.5 0 -0.5 --- P Diastolic R Q Systolic S 0.5 0.5 T 1.0 1.0 1.5 t (s) 1.5 t (s)
Consider a person working in an environment where electric currents might pass through their body. Construct a problem in which you calculate the resistance of insulation needed to protect the person from harm. Among the things to be considered are the voltage to which the person might be exposed,
(a) Referring to Figure 20.31, find the time systolic pressure lags behind the middle of the QRS complex. (b) Discuss the reasons for the time lag.Data given in Figure 20.31 Arterial blood pressure (mm Hg) Lead Il voltage (m V) 120 100 1.0 0.5 0 -0.5
Critical Thinking A copper wire of length 1.25 m is in a circuit. A current of 2.50 A flows through the wire.(a) Initially, the circuit is at 20.0°C. If there is an energy loss of 3.25 MJ in the first second caused by the wire as soon as the circuit is turned on, what is the radius of the
A car has two horns, one emitting a frequency of 199 Hz and the other emitting a frequency of 203 Hz. What beat frequency do they produce?
The middle-C hammer of a piano hits two strings, producing beats of 1.50 Hz. One of the strings is tuned to 260.00 Hz. What frequencies could the other string have?
Two tuning forks having frequencies of 460 and 464 Hz are struck simultaneously. What average frequency will you hear, and what will the beat frequency be?
Twin jet engines on an airplane are producing an average sound frequency of 4100 Hz with a beat frequency of 0.500 Hz. What are their individual frequencies?
A wave traveling on a Slinky® that is stretched to 4 m takes 2.4 s to travel the length of the Slinky and back again.(a) What is the speed of the wave?(b) Using the same Slinky stretched to the same length, a standing wave is created which consists of three antinodes and four nodes. At what
Ultrasound of intensity 1.50 x 102 W/m2 is produced by the rectangular head of a medical imaging device measuring 3.00 by 5.00 cm. What is its power output?
The low-frequency speaker of a stereo set has a surface area of 0.05 m2 and produces 1W of acoustical power. What is the intensity at the speaker? If the speaker projects sound uniformly in all directions, at what distance from the speaker is the intensity 0.1 W/m2?
To increase intensity of a wave by a factor of 50, by what factor should the amplitude be increased?
A device called an insolation meter is used to measure the intensity of sunlight has an area of 100 cm2 and registers 6.50 W. What is the intensity in W/m2?
Suppose you have a device that extracts energy from ocean breakers in direct proportion to their intensity. If the device produces 10.0 kW of power on a day when the breakers are 1.20 m high, how much will it produce when they are 0.600 m high?
(a) A photovoltaic array of (solar cells) is 10.0% efficient in gathering solar energy and converting it to electricity. If the average intensity of sunlight on one day is 700 W/m2, what area should your array have to gather energy at the rate of 100 W? (b) What is the maximum cost of the array if
A microphone receiving a pure sound tone feeds an oscilloscope, producing a wave on its screen. If the sound intensity is originally 2.00 x 10-5 W/m2, but is turned up until the amplitude increases by 30.0%, what is the new intensity?
(a) What is the intensity in W/m2 of a laser beam used to burn away cancerous tissue that, when 90.0% absorbed, puts 500 J of energy into a circular spot 2.00 mm in diameter in 4.00 s?(b) Discuss how this intensity compares to the average intensity of sunlight (about 700 W/m2) and the implications
When poked by a spear, an operatic soprano lets out a 1200-Hz shriek. What is its wavelength if the speed of sound is 345 m/s?
What frequency sound has a 0.10-m wavelength when the speed of sound is 340 m/s?
Calculate the speed of sound on a day when a 1500 Hz frequency has a wavelength of 0.221 m.
(a) What is the speed of sound in a medium where a 100-kHz frequency produces a 5.96-cm wavelength?(b) Which substance in Table 17.1 is this likely to be?Data given in Table 17.1 Medium Gases at 0°C Air Carbon dioxide Oxygen Helium Hydrogen Liquids at 20°C Ethanol Mercury Water, fresh Sea
Show that the speed of sound in 20.0°C air is 343 m/s, as claimed in the text.
(a) How much heat transfer is necessary to raise the temperature of a 0.200-kg piece of ice from -20.0°C to 130°C, including the energy needed for phase changes?(b) How much time is required for each stage, assuming a constant 20.0 kJ/s rate of heat transfer?
Why does it hurt more if your hand is snapped with a ruler than with a loose spring, even if the displacement of each system is equal?
Imagine you observe two fireworks explode. You hear the explosion of one as soon as you see it. However, you see the other firework for several milliseconds before you hear the explosion. Explain why this is so.
You observe two musical instruments that you cannot identify. One plays high-pitch sounds and the other plays lowpitch sounds. How could you determine which is which without hearing either of them play?
Describe how amplitude is related to the loudness of a sound.
Identify common sounds at the levels of 10 dB, 50 dB, and 100 dB.
Why did scientist Christian Doppler observe musicians both on a moving train and also from a stationary point not on the train?
Describe a situation in your life when you might rely on the Doppler shift to help you either while driving a car or walking near traffic.
Describe how noise-canceling headphones differ from standard headphones used to block outside sounds.
How is it possible to use a standing wave's node and antinode to determine the length of a closed-end tube?
Are ultrasound and infrasound imperceptible to all hearing organisms? Explain your answer.
Why is it possible to use ultrasound both to observe a fetus in the womb and also to destroy cancerous tumors in the body?
Can you explain the attraction of water to the charged rod in the figure below?
Can any arbitrary combination of resistors be broken down into series and parallel combinations? See if you can draw a circuit diagram of resistors that cannot be broken down into combinations of series and parallel.
Can Kirchhoff’s rules be applied to simple series and parallel circuits or are they restricted for use in more complicated circuits that are not combinations of series and parallel?
Digital meters are able to detect smaller currents than analog meters employing galvanometers. How does this explain their ability to measure voltage and current more accurately than analog meters?
Identify other factors that might limit the accuracy of null measurements. Would the use of a digital device that is more sensitive than a galvanometer improve the accuracy of null measurements?
When is the potential difference across a capacitor an emf?
(a) What is the potential difference going from point a to point b in Figure 21.45? (b) What is the potential difference going from c to b? (c) From e to g? (d) From e to d? a R₁ ww 200 0.50 18 V P₂ www 15 2 P₂ 在 0 1₂ 6 2 g 3.0V 0.25 02 R₂ w 82 24VI 百 12V 0.5 (2 "₁ m d 0.75 22
Could a person on intravenous infusion (an IV) be microshock sensitive?
How do sound vibrations of atoms differ from thermal motion?
When sound passes from one medium to another where its propagation speed is different, does its frequency or wavelength change? Explain your answer briefly.
Six members of a synchronized swim team wear earplugs to protect themselves against water pressure at depths, but they can still hear the music and perform the combinations in the water perfectly. One day, they were asked to leave the pool so the dive team could practice a few dives, and they tried
A community is concerned about a plan to bring train service to their downtown from the town’s outskirts. The current sound intensity level, even though the rail yard is blocks away, is 70 dB downtown. The mayor assures the public that there will be a difference of only 30 dB in sound in the
Is the Doppler shift real or just a sensory illusion?
Due to efficiency considerations related to its bow wake, the supersonic transport aircraft must maintain a cruising speed that is a constant ratio to the speed of sound (a constant Mach number). If the aircraft flies from warm air into colder air, should it increase or decrease its speed? Explain
When you hear a sonic boom, you often cannot see the plane that made it. Why is that?
How does an unamplified guitar produce sounds so much more intense than those of a plucked string held taut by a simple stick?
You are given two wind instruments of identical length. One is open at both ends, whereas the other is closed at one end. Which is able to produce the lowest frequency?
What is the difference between an overtone and a harmonic? Are all harmonics overtones? Are all overtones harmonics?
Why can a hearing test show that your threshold of hearing is 0 dB at 250 Hz, when Figure 17.35 implies that no one can hear such a frequency at less than 20 dB?
If audible sound follows a rule of thumb similar to that for ultrasound, in terms of its absorption, would you expect the high or low frequencies from your neighbor’s stereo to penetrate into your house? How does this expectation compare with your experience?
Elephants and whales are known to use infrasound to communicate over very large distances. What are the advantages of infrasound for long distance communication?
It is more difficult to obtain a high-resolution ultrasound image in the abdominal region of someone who is overweight than for someone who has a slight build. Explain why this statement is accurate.
Suppose you read that 210-dB ultrasound is being used to pulverize cancerous tumors. You calculate the intensity in watts per centimeter squared and find it is unreasonably high (105 W/cm2). What is a possible explanation?
There are very large numbers of charged particles in most objects. Why, then, don’t most objects exhibit static electricity?
Why do most objects tend to contain nearly equal numbers of positive and negative charges?
An eccentric inventor attempts to levitate by first placing a large negative charge on himself and then putting a large positive charge on the ceiling of his workshop. Instead, while attempting to place a large negative charge on himself, his clothes fly off. Explain.
If you have charged an electroscope by contact with a positively charged object, describe how you could use it to determine the charge of other objects. Specifically, what would the leaves of the electroscope do if other charged objects were brought near its knob?
When a glass rod is rubbed with silk, it becomes positive and the silk becomes negative—yet both attract dust. Does the dust have a third type of charge that is attracted to both positive and negative? Explain.
Why does a car always attract dust right after it is polished?
Describe how a positively charged object can be used to give another object a negative charge. What is the name of this process?
Figure 18.39 shows the charge distribution in a water molecule, which is called a polar molecule because it has an inherent separation of charge. Given water’s polar character, explain what effect humidity has on removing excess charge from objects. -2q Н b+6 104° b+2 H H
What is grounding? What effect does it have on a charged conductor? On a charged insulator?
Using Figure 18.39, explain, in terms of Coulomb’s law, why a polar molecule (such as in Figure 18.39) is attracted by both positive and negative charges. -2q H b+o $104° H b+
Given the polar character of water molecules, explain how ions in the air form nucleation centers for rain droplets.
Why must the test charge in the definition of the electric field be vanishingly small?
Are the direction and magnitude of the Coulomb force unique at a given point in space? What about the electric field?
Figure 18.40 shows an electric field extending over three regions, labeled I, II, and III. Answer the following questions. (a) Are there any isolated charges? If so, in what region and what are their signs? (b) Where is the field strongest? (c) Where is it weakest? (d) Where is the field the
Compare and contrast the Coulomb force field and the electric field. To do this, make a list of five properties for the Coulomb force field analogous to the five properties listed for electric field lines. Compare each item in your list of Coulomb force field properties with those of the electric
A cell membrane is a thin layer enveloping a cell. The thickness of the membrane is much less than the size of the cell. In a static situation the membrane has a charge distribution of -2.5 x 10-6C/m2 on its inner surface and +2.5 x 10-6 C/m2 on its outer surface. Draw a diagram of the cell and the
Is the object in Figure 18.41 a conductor or an insulator? Justify your answer.
If the electric field lines in the figure above were perpendicular to the object, would it necessarily be a conductor? Explain.
The discussion of the electric field between two parallel conducting plates, in this module states that edge effects are less important if the plates are close together. What does close mean? That is, is the actual plate separation crucial, or is the ratio of plate separation to plate area crucial?
Would the self-created electric field at the end of a pointed conductor, such as a lightning rod, remove positive or negative charge from the conductor? Would the same sign charge be removed from a neutral pointed conductor by the application of a similar externally created electric field? (The
Why is a golfer with a metal club over her shoulder vulnerable to lightning in an open fairway? Would she be any safer under a tree?
Can the belt of a Van de Graaff accelerator be a conductor? Explain.
Are you relatively safe from lightning inside an automobile? Give two reasons.
Using the symmetry of the arrangement, show that the net Coulomb force on the charge at the center of the square below (Figure 18.42) is zero if the charges on the four corners are exactly equal. qa O qc Oq qb O ad

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