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physics
modern physics
Physics 5th edition James S. Walker - Solutions
REFERRING TO EXAMPLE 23-8 Suppose the direction of the magnetic field is reversed. Everything else in the system remains the same.(a) Is the magnetic force exerted on the rod to the right, to the left, or zero? Explain.(b) Is the direction of the induced current clockwise, counterclockwise, or
FigurE 23-32 shows the magnetic flux through a coil as a function of time. At what times shown in this plot do (a) The magnetic flux and (b) The induced emf have the greatest magnitude?Figure 23-32
Figure 23-33 shows the magnetic flux through a single-loop coil as a function of time. What is the induced emf in the coil at (a) t = 0.050 s, (b) t = 0.15 s, and (c) t = 0.50 s?Figure 23-33
One type of antenna for receiving AM radio signals is a square loop of wire, 0.15 m on a side, that has 25 turns. If the magnetic field from the radio waves changes at a rate of 9.2 × 10-4 T/s and is perpendicular to the loop, what is the magnitude of the induced emf in the loop?
A wire loop is placed in a magnetic field that is perpendicular to its plane. The field varies with time as shown in FIGURE 23-34.Rank the six regions of time in order of increasing magnitude of the induced emf. Indicate ties where appropriate.FIGURE 23-34.
FIGURE 23-35 shows four different situations in which a metal ring moves to the right with constant speed through a region with a varying magnetic field. The intensity of the color indicates the intensity of the field, and in each case the field either increases or decreases at a uniform rate from
Consider a single-loop coil whose magnetic flux is given by Figure 23-32.(a) Is the magnitude of the induced emf in this coil greater near t = 0.4 s or near t = 0.5 s? Explain.(b) At what times in this plot do you expect the induced emf in the coil to have a maximum magnitude? Explain.(c) Estimate
A single conducting loop of wire has an area of 7.2 × 10-2 m2 and a resistance of 110 Ω. Perpendicular to the plane of the loop is a magnetic field of strength 0.88 T. At what rate (in T/s) must this field change if the induced current in the loop is to be 0.43 A?
The area of a 120-turn coil oriented with its plane perpendicular to a 0.33-T magnetic field is 0.050 m2. Find the average induced emf in this coil if the magnetic field reverses its direction in 0.11 s.
A uniform magnetic field of 0.0250 T points vertically upward. Find the magnitude of the magnetic flux through each of the five sides of the open-topped rectangular box shown in FIGURE 23-31, given that the dimensions of the box are L = 32.5 cm, W = 12.0 cm, and H = 10.0 cm.Figure 23-31
An emf is induced in a conducting loop of wire 1.40 m long as its shape is changed from square to circular. Find the average magnitude of the induced emf if the change in shape occurs in 0.125 s and the local 0.455-T magnetic field is perpendicular to the plane of the loop.
A magnetic field increases from 0 to 0.55 T in 1.6 s. How many turns of wire are needed in a circular coil 12 cm in diameter to produce an induced emf of 9.0 V?
A metal ring is dropped into a localized region of constant magnetic field, as indicated in FIGURE 23-36. The magnetic field is zero above and below the region where it is finite.(a) For each of the three indicated locations 11, 2, and 32, is the induced current clockwise, counterclockwise, or
A metal ring is dropped into a localized region of constant magnetic field, as indicated in Figure 23-36. The magnetic field is zero above and below the region where it is finite.(a) For each of the three indicated locations 11, 2, and 32, is the magnetic force exerted on the ring upward, downward,
FIGURE 23-37 shows two metal disks of the same size and material oscillating in and out of a region with a magnetic field. One disk is solid; the other has a series of slots.(a) Is the damping effect of eddy currents on the solid disk greater than, less than, or equal to the damping effect on the
(a) As the solid metal disk in Figure 23-37 swings to the right, from the region with no field into the region with a finite magnetic field, is the induced current in the disk clockwise, counterclockwise, or zero?(b) Choose the best explanation from among the following:I. The induced current is
A bar magnet with its north pole pointing downward is falling toward the center of a horizontal conducting ring. As viewed from above, is the direction of the induced current in the ring clockwise or counterclockwise? Explain.
A loop of wire is dropped and allowed to fall between the poles of a horseshoe magnet, as shown in FIGURE 23-38. State whether the induced current in the loop is clockwise or counterclockwise when (a) the loop is above the magnet and (b) the loop is below the magnet.Figure 23-38
Suppose we change the situation shown in Figure 23- 38 as follows: Instead of allowing the loop to fall on its own, we attach a string to it and lower it with constant speed along the path indicated by the dashed line. Is the tension in the string greater than, less than, or equal to the weight of
Figure 23-39 shows a current-carrying wire and a circuit containing a resistor R.(a) If the current in the wire is constant, is the induced current in the circuit clockwise, counterclockwise, or zero? Explain.(b) If the current in the wire increases, is the induced current in the circuit clockwise,
A magnetic field is oriented at an angle of 67° to the normal of a rectangular area 5.9 cm by 7.8 cm. If the magnetic flux through this surface has a magnitude of 4.8 × 10-5 T • m2, what is the strength of the magnetic field?
Consider the physical system shown in Figure 23-39. If the current in the wire changes direction, is the induced current in the circuit clockwise, counterclockwise, or zero? Explain.Figure 23-39
A long, straight wire carries a current I, as indicated in FIGURE 23-40. Three small metal rings are placed near the current-carrying wire (A and C) or directly on top of it (B). If the current in the wire is increasing with time, indicate whether the induced emf in each of the rings is clockwise,
Figure 23-41 shows a circuit with an area of 0.060 m2 containing a R = 1.0-Ω resistor and a C = 250-mF uncharged capacitor.Pointing into the plane of the circuit is a uniform magnetic field of magnitude 0.25 T. In 0.010 s the magnetic field reverses direction at a constant rate to
Figure 23-41 shows a circuit with an area of 0.060 m2 containing a R = 1.0-Ω resistor and a C = 250-µF uncharged capacitor. Pointing into the plane of the circuit is a uniform magnetic field of magnitude 0.15 T. In 0.010 s the magnetic field strengthens at a constant rate to become 0.80 T
A conducting rod slides on two wires in a region with a magnetic field. The two wires are not connected. Is a force required to keep the rod moving with constant speed? Explain.
A metal rod 0.95 m long moves with a speed of 2.4 m/s perpendicular to a magnetic field. If the induced emf between the ends of the rod is 0.65 V, what is the strength of the magnetic field?
A Boeing KC-135A airplane has a wingspan of 39.9 m and flies at constant altitude in a northerly direction with a speed of 850 km/h. If the vertical component of the Earth's magnetic field is 5.0 × 10-5 T, and its horizontal component is 1.4 × 10-5 T, what is the induced emf between the wing tips?
Figure 23-42 shows a zero-resistance rod sliding to the right on two zero-resistance rails separated by the distance L = 0.500 m. The rails are connected by a 10.0-Ω resistor, and the entire system is in a uniform magnetic field with a magnitude of 0.750 T.(a) Find the speed at which the bar
Referring to part (a) of Problem 37, (a) find the force that must be exerted on the rod to maintain a constant current of 0.175 A in the resistor. (b) What is the rate of energy dissipation in the resistor? (c) What is the mechanical power delivered to the rod?Part (a) of Problem
(a) Find the current that flows in the circuit shown in Example 23-8. (b) What speed must the rod have if the current in the circuit is to be 1.0 A?
The magnetic field produced by an MRI solenoid 2.5 m long and 1.2 m in diameter is 1.7 T. Find the magnitude of the magnetic flux through the core of this solenoid.
Suppose the mechanical power delivered to the rod in Example 23-8 is 8.9 W. Find (a) The current in the circuit and (b) The speed of the rod.
The maximum induced emf in a generator rotating at 210 rpm is 35 V. How fast must the rotor of the generator rotate if it is to generate a maximum induced emf of 55 V?
A rectangular coil 25 cm by 45 cm has 150 turns. This coil produces a maximum emf of 75 V when it rotates with an angular speed of 190 rad/s in a magnetic field of strength B. Find the value of B.
A 1.6-m wire is wound into a coil with a radius of 3.2 cm. If this coil is rotated at 85 rpm in a 0.075-T magnetic field, what is its maximum emf?
A shake flashlight uses the mechanical energy of the shaking action to charge a capacitor that operates the LED light.(a) If you shake the flashlight with an average force of 2.0 N at a speed of 0.85 m/s, what mechanical power do you produce?(b) If you shake the flashlight for 30 seconds, and 75%
A circular coil with a diameter of 22.0 cm and 155 turns rotates about a vertical axis with an angular speed of 1250 rpm. The only magnetic field in this system is that of the Earth. At the location of the coil, the horizontal component of the magnetic field is 3.80 × 10-5 T, and the vertical
A generator is designed to produce a maximum emf of 190 V while rotating with an angular speed of 3800 rpm. Each coil of the generator has an area of 0.016 m2. If the magnetic field used in the generator has a magnitude of 0.052 T, how many turns of wire are needed?
Find the induced emf when the current in a 48.0-mH inductor increases from 0 to 535 mA in 15.5 ms.
How many turns should a solenoid of cross-sectional area 0.035 m2 and length 0.32 m have if its inductance is to be 65 mH?
The inductance of a solenoid with 450 turns and a length of 24 cm is 7.3 mH. (a) What is the cross-sectional area of the solenoid? (b) What is the induced emf in the solenoid if its current drops from 3.2 A to 0 in 55 ms?
Find the magnitude of the magnetic flux through the floor of a house that measures 22 m by 18 m. Assume that the Earth's magnetic field at the location of the house has a horizontal component of 2.6 × 10-5 T pointing north, and a downward vertical component of 4.2 × 10-5 T.
Determine the inductance of a solenoid with 660 turns in a length of 34 cm. The circular cross section of the solenoid has a radius of 4.6 cm.
A solenoid with a cross-sectional area of 1.14 × 10-3 m2 is 0.610 m long and has 985 turns per meter. Find the induced emf in this solenoid if the current in it is increased from 0 to 2.00 A in 33.3 ms.
A solenoid has N turns of area A distributed uniformly along its length, l. When the current in this solenoid increases at the rate of 2.0 A/s, an induced emf of 75 mV is observed.(a) What is the inductance of this solenoid?(b) Suppose the spacing between coils is doubled. The result is a solenoid
How much time does it take for the current in an RL circuit with R = 130 Ω and L = 68 mH to reach half its final value?
A simple RL circuit includes a 0.125-H inductor. If the circuit is to have a characteristic time of 0.500 ms, what should be the value of the resistance?
The four electric circuits shown in FIGURE 23-43 have identical batteries, resistors, and inductors. Rank the circuits in order of increasing current supplied by the battery long after the switch is closed. Indicate ties where appropriate.FIGURE 23-43
The circuit shown in figure 23-44 consists of a 6.0-V battery, a 31-mH inductor, and four 61-Ω resistors. (a) Find the characteristic time for this circuit. What is the current supplied by this battery (b) Two characteristic time intervals after closing the switch and (c) A long
The current in an RL circuit increases to 95% of its final value 2.24 s after the switch is closed. (a) What is the characteristic time for this circuit?(b) If the inductance in the circuit is 0.275 H, what is the resistance?
An AWG 24 copper wire with a diameter of 0.511 mm is tightly wrapped (one turn per wire diameter) around a2.54-cm-diameter tube. As the number of turns increases, the inductance L of the resulting solenoid increases, and so does the resistance R of the wire because its length increases.(a) Write an
Consider the RL circuit shown in FIGURE 23-45. When the switch is closed, the current in the circuit is observed to increase from 0 to 0.32 A in 0.15 s.(a) What is the inductance L?(b) At what time after the switch is closed (t = 0) does the current have the value 0.50 A?(c) What is the maximum
At a certain location, the Earth's magnetic field has a magnitude of 5.4 × 10-5 T and points in a direction that is 68° below the horizontal. Find the magnitude of the magnetic flux through the top of a desk at this location that measures 76 cm by 45 cm.
Consider the circuit shown in Figure 23-45. Assuming the inductor in this circuit has the value L = 9.5 mH, how much energy is stored in the inductor after the switch has been closed for a long time?
A solenoid is 1.8 m long and has 450 turns per meter. What is the cross-sectional area of this solenoid if it stores 0.39 J of energy when it carries a current of 12 A?
In the Alcator fusion experiment at MIT, a magnetic field of 50.0 T is produced.(a) What is the magnetic energy density in this field?(b) Find the magnitude of the electric field that would have the same energy density found in part (a).
An engineer proposes to store 75 kJ of energy by flowing 1.5 kA of current through a superconducting solenoid that forms an inductor. (a) What is the required inductance L? (b) If the solenoid is to have a radius of 1.2 m and be wound with no more than 5 turns per meter, what length must the
After the switch in figure 23-46 has been closed for a long time, the energy stored in the inductor is 0.110 J.(a) What is the value of the resistance R?(b) If it is desired that more energy be stored in the inductor, should the resistance R be greater than or less than the value found in part (a)?
Suppose the resistor in Figure 23-46 has the value R = 14 Ω and that the switch is closed at time t = 0.(a) How much energy is stored in the inductor at the time t = τ?(b) How much energy is stored in the inductor at the time t = 2τ?(c) If the value of R is increased, does the characteristic
An ac generator produces a peak voltage of 75 V. What is the rms voltage of this generator?
The capacitive reactance of a capacitor at 60.0 Hz is 105 Ω. At what frequency is its capacitive reactance 72.5 Ω?
A 105-μF capacitor is connected to an ac generator with an rms voltage of 32.5 V and a frequency of 125 Hz. What is the rms current in this circuit?
The rms voltage across a 0.010-μF capacitor is 2.8 V at a frequency of 75 Hz. What are (a) The rms (b) The maximum current through the capacitor?
The rms current through a 55.5-μF capacitor is 1.51 A when it is connected to an ac generator. (a) If a second capacitor is connected in series with the first, will the rms current increase or decrease?(b) Calculate the rms current when a 38.7-μF capacitor is connected in series with the
The maximum current in a 22-μF capacitor connected to an ac generator with a frequency of 120 Hz is 0.15 A.(a) What is the maximum voltage of the generator?(b) What is the voltage across the capacitor when the current in the circuit is 0.10 A and increasing?(c) What is the voltage across the
An rms voltage of 20.5 V with a frequency of 1.00 kHz is applied to a 0.395-μF capacitor. (a) What is the rms current in this circuit? (b) By what factor does the current change if the frequency of the voltage is doubled? (c) Calculate the current for a frequency of 2.00 kHz.
A circuit consists of a 2.00-kHz generator and a capacitor. When the rms voltage of the generator is 0.800 V, the rms current in the circuit is 0.515 mA. (a) What is the reactance of the capacitor at 2.00 kHz? (b) What is the capacitance of the capacitor? (c) If the rms voltage is maintained at
A 0.22-μF capacitor is connected to an ac generator with an rms voltage of 12 V. For what range of frequencies will the rms current in the circuit be less than 1.0 mA?
At what frequency will a generator with an rms voltage of 504 V produce an rms current of 7.50 mA in a 0.0150-μF capacitor?
A 22.0-μF capacitor is connected to an ac generator with an rms voltage of 118 V and a frequency of 60.0 Hz.(a) What is the rms current in the circuit?(b) If you wish to increase the rms current, should you add a second capacitor in series or in parallel?(c) Find the value of the capacitance that
In many European homes the rms voltage available from a wall socket is 240 V. What is the maximum voltage in this case?
Find the impedance of a 60.0-Hz circuit with a 65.5-Ω resistor connected in series with a 85.0-μF capacitor.
An ac generator with a frequency of 125 Hz and an rms voltage of 42.5 V is connected in series with a 10.0-kΩ resistor and a 0.250-μF capacitor. What is the rms current in this circuit?
The rms current in an RC circuit is 0.72 A. The capacitor in this circuit has a capacitance of 13 μF and the ac generator has a frequency of 150 Hz and an rms voltage of 95 V. What is the resistance in this circuit?
When an ac generator with a frequency of 180 Hz and an rms voltage of 36 V is connected to an RC circuit, the rms current is 0.28 A. If the resistance has a value of 54 Ω, what is the value of the capacitance?
A 50.0-Hz generator with an rms voltage of 115 V is connected in series to a 3.12-kΩ resistor and a 1.65-μF capacitor. Find(a) The rms current in the circuit(b) The phase angle, ф, between the current and the voltage.
(a) At what frequency must the circuit in Problem 24 be operated for the current to lead the voltage by 25.0°?(b) Using the frequency found in part (a), find the average power consumed by this circuit.In problem 24A 50.0-Hz generator with an rms voltage of 115 V is connected in series to a
Find the power factor for an RC circuit connected to a 60.0-Hz generator with an rms voltage of 195 V. The values of R and C in this circuit are 105 Ω and 82.4-μF, respectively.
(a) Determine the power factor for an RC circuit with R = 4.0 kΩ and C = 0.35 mF that is connected to an ac generator with an rms voltage of 24 V and a frequency of 150 Hz.(b) Will the power factor for this circuit increase, decrease, or stay the same if the frequency of the generator is
The "square-wave" voltage shown in FIGURE 24-31 is applied to an RC circuit. Sketch the shape of the instantaneous voltage across the capacitor, assuming the time constant of the circuit is equal to the period of the applied voltage.In figure 24-31
When a long copper wire of finite resistance is connected to an ac generator, as shown in FIGURE 24-32 (a), a certain amount of current flows through the wire. The wire is now wound into a coil of many loops and reconnected to the generator, as indicated in FIGURE 24-32 (b).In figure 24-32(a) Is
An rms voltage of 120 V produces a maximum current of 4.1 A in a certain resistor. Find the resistance of this resistor.
An inductor has a reactance of 56.5 Ω at 85.0 Hz. What is its reactance at 60.0 Hz?
What is the rms current in a 97.5-mH inductor when it is connected to a 60.0-Hz generator with an rms voltage of 135 V?
What rms voltage is required to produce an rms current of 2.1 A in a 66-mH inductor at a frequency of 25 Hz?
A loudspeaker's impedance is listed as 8.0 Ω at 2.0 kHz. Assuming its resistance and capacitance are negligibly small, what is the inductance of the speaker coil?
An inductor is used to limit the current through a fluorescent lamp that is operated with an rms voltage of 120 V at ƒ = 60 Hz. If the maximum rms current should be 0.33 A, and assuming the lamp has zero resistance, what value of inductance L should be used as the ballast?
A 525-Ω resistor and a 295-H inductor are connected in series with an ac generator with an rms voltage of 20.0 V and a frequency of 60.0 Hz. What is the rms current in this circuit?
The rms current in an RL circuit is 0.26 A when it is connected to an ac generator with a frequency of 60.0 Hz and an rms voltage of 25 V.(a) Given that the inductor has an inductance of 145 mH, what is the resistance of the resistor?(b) Find the rms voltage across the resistor.(c) Find the rms
An ac generator with a frequency of 1.55 kHz and an rms voltage of 20.8 V is connected in series with a 2.00-kΩ resistor and a 292-mH inductor.(a) What is the power factor for this circuit?(b) What is the average power consumed by this circuit?
An rms voltage of 22.2 V with a frequency of 1.00 kHz is applied to a 0.290-mH inductor.(a) What is the rms current in this circuit?(b) By what factor does the current change if the frequency of the voltage is doubled?(c) Calculate the current for a frequency of 2.00 kHz.
A 0.22-μH inductor is connected to an ac generator with an rms voltage of 12 V. For what range of frequencies will the rms current in the circuit be less than 1.0 mA?
The rms current in an ac circuit with a resistance of 150 Ω is 0.15 A. What are(a) The average(b) The maximum power consumed by this circuit?
The phase angle in a certain RL circuit is 68° at a frequency of 60.0 Hz. If R = 2.1 Ω for this circuit, what is the value of the inductance, L?
(a) Sketch the phasor diagram for an ac circuit with a 105-Ω resistor in series with a 22.5-mH inductor. The frequency of the generator is 60.0 Hz.(b) If the rms voltage of the generator is 120 V, what is the average power consumed by the circuit?
A large air conditioner has a resistance of 7.0 Ω and an inductive reactance of 15 Ω. If the air conditioner is powered by a 60.0-Hz generator with an rms voltage of 240 V, find(a) The impedance of the air conditioner,(b) Its rms current,(c) The average power consumed by the air conditioner.
The "square-wave" voltage shown in Figure 24-31 is applied to an RL circuit. Sketch the shape of the instantaneous voltage across the inductor, assuming the time constant of the circuit is much less than the period of the applied voltage.In figure 24-31
An inductor and a capacitor are to be connected to a generator. Will the generator supply more current at high frequency if the inductor and capacitor are connected in series or in parallel? Explain.
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