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physics
college physics 2nd

College Physics 2nd Edition OpenStax - Solutions

(a) What is the value of the peak voltage for 120-V AC power?(b) What is the peak power consumption rate of a 60.0-W AC light bulb?StrategyWe are told that Vrms is 120 V and Pave is 60.0 W. We can use to find the peak voltage, and we can manipulate the definition of power to find the peak power
(a) What current is needed to transmit 100 MW of power at 200 kV?(b) What is the power dissipated by the transmission lines if they have a resistance of 1.00 Ω? (c) What percentage of the power is lost in the transmission lines?StrategyWe are given Pave = 100 MW, Vrms = 200 kV, and the resistance
Figure 21.6 shows the resistors from the previous two examples wired in a different way-a combination of series and parallel. We can consider R1 to be the resistance of wires leading to R2 and R3.(a) Find the total resistance.(b) What is the IR drop in R1?(c) Find the current I2 through R2.(d) What
A certain battery has a 12.0-V emf and an internal resistance of 0.100 Ω.(a) Calculate its terminal voltage when connected to a 10.0-Ω load.(b) What is the terminal voltage when connected to a 0.500-Ω load?(c) What power does the 0.500-Ω load dissipate?(d) If the internal resistance grows to
A heart defibrillator is used to resuscitate an accident victim by discharging a capacitor through the trunk of her body. A simplified version of the circuit is seen in Figure 21.38.(a) What is the time constant if an 8.00-μF capacitor is used and the path resistance through her body is 1.00 x 103
Volcanic and other such activity at the mid-Atlantic ridge extrudes material to fill the gap between separating tectonic plates associated with continental drift. The magnetization of rocks is found to reverse in a coordinated manner with distance from the ridge. What does this imply about the
With the exception of compasses, you seldom see or personally experience forces due to the Earth's small magnetic field. To illustrate this, suppose that in a physics lab you rub a glass rod with silk, placing a 20-nC positive charge on it. Calculate the force on the rod due to the Earth's magnetic
Explain why the magnetic field would not be unique (that is, not have a single value) at a point in space where magnetic field lines might cross. (Consider the direction of the field at such a point.)
A magnet brought near an old-fashioned TV screen such as in Figure 22.20 (TV sets with cathode ray tubes instead of LCD screens) severely distorts its picture by altering the path of the electrons that make its phosphors glow. (Don't try this at home, as it will permanently magnetize and ruin the
List the ways in which magnetic field lines and electric field lines are similar. For example, the field direction is tangent to the line at any point in space. Also list the ways in which they differ. For example, electric force is parallel to electric field lines, whereas magnetic force on moving
A Hall effect flow probe is placed on an artery, applying a 0.100-T magnetic field across it, in a setup similar to that in Figure 22.28. What is the Hall emf, given the vessel’s inside diameter is 4.00 mm and the average blood velocity is 20.0 cm/s?StrategyBecause B, v, and I are mutually
Noting that the magnetic field lines of a bar magnet resemble the electric field lines of a pair of equal and opposite charges, do you expect the magnetic field to rapidly decrease in strength with distance from the magnet? Is this consistent with your experience with magnets?
(a) What is the current involved when a truck battery sets in motion 720 C of charge in 4.00 s while starting an engine?(b) How long does it take 1.00 C of charge to flow through a handheld calculator if a 0.300-mA current is flowing?StrategyWe can use the definition of current in the equation I =
If the 0.300-mA current through the calculator mentioned in the Example 20.1 example is carried by electrons, how many electrons per second pass through it?StrategyThe current calculated in the previous example was defined for the flow of positive charge. For electrons, the magnitude is the same,
Calculate the drift velocity of electrons in a 12-gauge copper wire (which has a diameter of 2.053 mm) carrying a 20.0-A current, given that there is one free electron per copper atom. (Household wiring often contains 12-gauge copper wire, and the maximum current allowed in such wire is usually 20
What is the resistance of an automobile headlight through which 2.50 A flows when 12.0 V is applied to it?StrategyWe can rearrange Ohm's law as stated by I = V/R and use it to find the resistance.
A car headlight filament is made of tungsten and has a cold resistance of 0.350 Ω. If the filament is a cylinder 4.00cm long (it may be coiled to save space), what is its diameter?StrategyWe can rearrange the equation R = ρL/A to find the cross-sectional area A of the filament from the given
Although caution must be used in applying ρ = ρ0(1+αΔT) and R = R0(1+ αΔT) for temperature changes greater than 100°C, for tungsten the equations work reasonably well for very large temperature changes. What, then, is the resistance of the tungsten filament in the previous example if its
Calculate the force on the wire shown in Figure 22.29, given B = 1.50 T, L = 5.00 cm, and I = 20.0 A.StrategyThe force can be found with the given information by using F = IlB sin θ and noting that the angle θ between I and B is 90°, so that sin θ = 1. RHR-1 F B N LL B S
Is the Earth’s magnetic field parallel to the ground at all locations? If not, where is it parallel to the surface? Is its strength the same at all locations? If not, where is it greatest?
Find the maximum torque on a 100-turn square loop of a wire of 10.0 cm on a side that carries 15.0 A of current in a 2.00-T field.StrategyTorque on the loop can be found using τ = NIAB sin θ. Maximum torque occurs when θ = 90° and sin θ = 1.
Find the current in a long straight wire that would produce a magnetic field twice the strength of the Earth’s at a distance of 5.0 cm from the wire.Strategy The Earth's field is about 5.0 x 10-5 T, and so here B due to the wire is taken to be 1.0 x 10-4 T. The equation HOI B = can be used to
What is the field inside a 2.00-m-long solenoid that has 2000 loops and carries a 1600-A current?StrategyTo find the field strength inside a solenoid, we use B =μ0nI. First, we note the number of loops per unit length is n N I 2000 2.00 m 1000 m¹ = 10 cm-¹.
How can the motion of a charged particle be used to distinguish between a magnetic and an electric field?
High-velocity charged particles can damage biological cells and are a component of radiation exposure in a variety of locations ranging from research facilities to natural background. Describe how you could use a magnetic field to shield yourself.
What are the signs of the charges on the particles in Figure 22.43? X X X X X X X X X X a X b X X Bin X X CX
If a cosmic ray proton approaches the Earth from outer space along a line toward the center of the Earth that lies in the plane of the equator, in what direction will it be deflected by the Earth’s magnetic field? What about an electron? A neutron?
Which of the particles in Figure 22.44 has the greatest velocity, assuming they have identical charges and masses? a O ● Bout
Which of the particles in Figure 22.44 has the greatest mass, assuming all have identical charges and velocities? a ● Bout
While operating, a high-precision TV monitor is placed on its side during maintenance. The image on the monitor changes color and blurs slightly. Discuss the possible relation of these effects to the Earth’s magnetic field.
Draw a sketch of the situation in Figure 22.29 showing the direction of electrons carrying the current, and use RHR-1 to verify the direction of the force on the wire. RHR-1 F B N F B S
Discuss how the Hall effect could be used to obtain information on free charge density in a conductor.
Verify that the direction of the force in an MHD drive, such as that in Figure 22.31, does not depend on the sign of the charges carrying the current across the fluid. N e B S RHR-1 F = I(B B F +
Why would a magnetohydrodynamic drive work better in ocean water than in fresh water? Also, why would superconducting magnets be desirable?
Draw a diagram and use RHR-1 to show that the forces on the top and bottom segments of the motor’s current loop in Figure 22.33 are vertical and produce no torque about the axis of rotation. F N KW I B B S F S
Which is more likely to interfere with compass readings, AC current in your refrigerator or DC current when you start your car? Explain.
Make a drawing and use RHR-2 to find the direction of the magnetic field of a current loop in a motor (such as in Figure 22.33). Then show that the direction of the torque on the loop is the same as produced by like poles repelling and unlike poles attracting. F N KW I B B S F S
If you have three parallel wires in the same plane, as in Figure 22.45, with currents in the outer two running in opposite directions, is it possible for the middle wire to be repelled by both? Attracted by both? Explain. I₁ 1₂ I3
Is the force attractive or repulsive between the hot and neutral lines hung from power poles? Why?
Use the right hand rules to show that the force between the two loops in Figure 22.46 is attractive if the currents are in the same direction and repulsive if they are in opposite directions. Is this consistent with like poles of the loops repelling and unlike poles of the loops attracting? Draw
Suppose two long straight wires run perpendicular to one another without touching. Does one exert a net force on the other? If so, what is its direction? Does one exert a net torque on the other? If so, what is its direction? Justify your responses by using the right hand rules.
If one of the loops in Figure 22.46 is tilted slightly relative to the other and their currents are in the same direction, what are the directions of the torques they exert on each other? Does this imply that the poles of the bar magnet-like fields they create will line up with each other if the
Electric field lines can be shielded by the Faraday cage effect. Can we have magnetic shielding? Can we have gravitational shielding?
Measurements of the weak and fluctuating magnetic fields associated with brain activity are called magnetoencephalograms (MEGs). Do the brain’s magnetic fields imply coordinated or uncoordinated nerve impulses? Explain.
Discuss the possibility that a Hall voltage would be generated on the moving heart of a patient during MRI imaging. Also discuss the same effect on the wires of a pacemaker. (The fact that patients with pacemakers are not given MRIs is significant.)
A patient in an MRI unit turns his head quickly to one side and experiences momentary dizziness and a strange taste in his mouth. Discuss the possible causes.
You are told that in a certain region there is either a uniform electric or magnetic field. What measurement or observation could you make to determine the type? (Ignore the Earth’s magnetic field.)
An example of magnetohydrodynamics (MHD) comes from the flow of a river (salty water). This fluid interacts with the Earth’s magnetic field to produce a potential difference between the two river banks. How would you go about calculating the potential difference?
The direction of the electric field shown in each part of Figure 24.5 is that produced by the charge distribution in the wire. Justify the direction shown in each part, using the Coulomb force law and the definition of E= F/q, where q is a positive test charge. 2 +++ DO t = 0 E +++ t= 714 (b) t =
Draw gravitational field lines between 2 masses, electric field lines between a positive and a negative charge, electric field lines between 2 positive charges and magnetic field lines around a magnet. Qualitatively describe the differences between the fields and the entities responsible for the
Is the direction of the magnetic field shown in Figure 24.6 (a) consistent with the right-hand rule for current (RHR-2) in the direction shown in the figure? (a) B thus E (b) B (c) B
Why is the direction of the current shown in each part of Figure 24.6 opposite to the electric field produced by the wire’s charge separation? (a) B thus E (b) (c) B
In which situation shown in Figure 24.23 will the electromagnetic wave be more successful in inducing a current in the wire? Explain. E (a) B (b) E
In which situation shown in Figure 24.24 will the electromagnetic wave be more successful in inducing a current in the loop? Explain. E (a) Tuner Loop B (b) E Tuner Loop
Should the straight wire antenna of a radio be vertical or horizontal to best receive radio waves broadcast by a vertical transmitter antenna? How should a loop antenna be aligned to best receive the signals?
Under what conditions might wires in a DC circuit emit electromagnetic waves?
Figure 24.25 shows the interference pattern of two radio antennas broadcasting the same signal. Explain how this is analogous to the interference pattern for sound produced by two speakers. Could this be used to make a directional antenna system that broadcasts preferentially in certain directions?
Give an example of interference of electromagnetic waves.
Can an antenna be any length? Explain your answer.
If you live in a region that has a particular TV station, you can sometimes pick up some of its audio portion on your FM radio receiver. Explain how this is possible. Does it imply that TV audio is broadcast as FM?
Explain why people who have the lens of their eye removed because of cataracts are able to see lowfrequency ultraviolet.
How do fluorescent soap residues make clothing look “brighter and whiter” in outdoor light? Would this be effective in candlelight?
Give an example of resonance in the reception of electromagnetic waves.
Why don’t buildings block radio waves as completely as they do visible light?
Illustrate that the size of details of an object that can be detected with electromagnetic waves is related to their wavelength, by comparing details observable with two different types (for example, radar and visible light or infrared and X-rays).
Make a list of some everyday objects and decide whether they are transparent or opaque to each of the types of electromagnetic waves.
Your friend says that more patterns and colors can be seen on the wings of birds if viewed in ultraviolet light. Would you agree with your friend? Explain your answer.
The rate at which information can be transmitted on an electromagnetic wave is proportional to the frequency of the wave. Is this consistent with the fact that laser telephone transmission at visible frequencies carries far more conversations per optical fiber than conventional electronic
Give an example of energy carried by an electromagnetic wave.
In an MRI scan, a higher magnetic field requires higher frequency radio waves to resonate with the nuclear type whose density and location is being imaged. What effect does going to a larger magnetic field have on the most efficient antenna to broadcast those radio waves? Does it favor a smaller or
What is the wavelength of an earthquake that shakes you with a frequency of 10.0 Hz and gets to another city 84.0 km away in 12.0 s?
(a) Seismographs measure the arrival times of earthquakes with a precision of 0.100 s. To get the distance to the epicenter of the quake, they compare the arrival times of S- and P-waves, which travel at different speeds. Figure 16.44) If S- and P-waves travel at 4.00 and 7.20 km/s, respectively,
Air temperature in the Sahara Desert can reach 56.0°C (about 134°F). What is the speed of sound in air at that temperature?
A sonar echo returns to a submarine 1.20 s after being emitted. What is the distance to the object creating the echo?
A physicist at a fireworks display times the lag between seeing an explosion and hearing its sound, and finds it to be 0.400 s.(a) How far away is the explosion if air temperature is 24.0°C and if you neglect the time taken for light to reach the physicist? (b) Calculate the distance to the
What is the intensity in watts per meter squared of 85.0-dB sound?
A sound wave traveling in 20°C air has a pressure amplitude of 0.5 Pa. What is the intensity of the wave?
What intensity level does the sound in the preceding problem correspond to?
What sound intensity level in dB is produced by earphones that create an intensity of 4.00 x 102 W/m2?
Show that an intensity of 10-12 W/m2 is the same as 10-16 W/cm2.
(a) What is the decibel level of a sound that is twice as intense as a 90.0-dB sound?(b) What is the decibel level of a sound that is one-fifth as intense as a 90.0-dB sound?
(a) What is the intensity of a sound that has a level 7.00 dB lower than a 4.00 x 10-9 W/m2 sound?(b) What is the intensity of a sound that is 3.00 dB higher than a 4.00 x 10-9 W/m2 sound?
(a) How much more intense is a sound that has a level 17.0 dB higher than another?(b) If one sound has a level 23.0 dB less than another, what is the ratio of their intensities?
People with good hearing can perceive sounds as low in level as -8.00 dB at a frequency of 3000 Hz. What is the intensity of this sound in watts per meter squared?
If a large housefly 3.0 m away from you makes a noise of 40.0 dB, what is the noise level of 1000 flies at that distance, assuming interference has a negligible effect?
Ten cars in a circle at a boom box competition produce a 120-dB sound intensity level at the center of the circle. What is the average sound intensity level produced there by each stereo, assuming interference effects can be neglected?
The amplitude of a sound wave is measured in terms of its maximum gauge pressure. By what factor does the amplitude of a sound wave increase if the sound intensity level goes up by 40.0 dB?
If a sound intensity level of 0 dB at 1000 Hz corresponds to a maximum gauge pressure (sound amplitude) of 10-9 atm, what is the maximum gauge pressure in a 60-dB sound? What is the maximum gauge pressure in a 120-dB sound?
An 8-hour exposure to a sound intensity level of 90.0 dB may cause hearing damage. What energy in joules falls on a 0.800-cm-diameter eardrum so exposed?
Sound is more effectively transmitted into a stethoscope by direct contact than through the air, and it is further intensified by being concentrated on the smaller area of the eardrum. It is reasonable to assume that sound is transmitted into a stethoscope 100 times as effectively compared with
Loudspeakers can produce intense sounds with surprisingly small energy input in spite of their low efficiencies. Calculate the power input needed to produce a 90.0-dB sound intensity level for a 12.0-cm-diameter speaker that has an efficiency of 1.00%. (This value is the sound intensity level right
(a) What frequency is received by a person watching an oncoming ambulance moving at 110 km/h and emitting a steady 800-Hz sound from its siren? The speed of sound on this day is 345 m/s.(b) What frequency does she receive after the ambulance has passed?
(a) At an air show a jet flies directly toward the stands at a speed of 1200 km/h, emitting a frequency of 3500 Hz, on a day when the speed of sound is 342 m/s. What frequency is received by the observers?(b) What frequency do they receive as the plane flies directly away from them?
What frequency is received by a mouse just before being dispatched by a hawk flying at it at 25.0 m/s and emitting a screech of frequency 3500 Hz? Take the speed of sound to be 331 m/s.
A commuter train blows its 200-Hz horn as it approaches a crossing. The speed of sound is 335 m/s.(a) An observer waiting at the crossing receives a frequency of 208 Hz. What is the speed of the train? (b) What frequency does the observer receive as the train moves away?
Can you perceive the shift in frequency produced when you pull a tuning fork toward you at 10.0 m/s on a day when the speed of sound is 344 m/s? To answer this question, calculate the factor by which the frequency shifts and see if it is greater than 0.300%.
Two eagles fly directly toward one another, the first at 15.0 m/s and the second at 20.0 m/s. Both screech, the first one emitting a frequency of 3200 Hz and the second one emitting a frequency of 3800 Hz. What frequencies do they receive if the speed of sound is 330 m/s?
What is the minimum speed at which a source must travel toward you for you to be able to hear that its frequency is Doppler shifted? That is, what speed produces a shift of 0.300% on a day when the speed of sound is 331 m/s?
A “showy” custom-built car has two brass horns that are supposed to produce the same frequency but actually emit 263.8 and 264.5 Hz. What beat frequency is produced?
What beat frequencies result if a piano hammer hits three strings that emit frequencies of 127.8, 128.1, and 128.3 Hz?

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