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physics
modern physics
Physics 5th edition James S. Walker - Solutions
What is the acceleration of a proton moving with a speed of 7.5 m/s at right angles to a magnetic field of 1.4 T?
Two long, straight wires are separated by a distance of 9.25 cm. One wire carries a current of 2.75 A, the other carries a current of 4.33 A.(a) Find the force per meter exerted on the 2.75-A wire.(b) Is the force per meter exerted on the 4.33-A wire greater than, less than, or the same as the
Two long, straight wires are oriented perpendicular to the page, as shown in FIGURE 22-50. The current in one wire is I1 = 3.0 A, pointing into the page, and the current in the other wire is I2 = 4.0 A, pointing out of the page. Find the magnitude and direction of the net magnetic field at point
A loop of wire is connected to the terminals of a battery, as indicated in FIGURE 22-51. If the loop is to attract the bar magnet which of the terminals, A or B, should be the positive terminal of the battery? Explain.Figure 22-51
The number of turns in a solenoid is doubled, and at the same time its length is doubled.(a) Does the magnetic field within the solenoid increase, decrease, or stay the same?(b) Choose the best explanation from among the following:I. Doubling the number of turns in a solenoid doubles its magnetic
A circular coil of wire has a radius of 7.5 cm and has 125 turns of wire that carries 6.6 A of current. What is the magnetic field at the center of the coil?
The solenoid for an automobile power door lock is 2.5 cm long and has 190 turns of wire that carry 1.6 A of current. What is the magnitude of the magnetic field that it produces?
It is desired that a solenoid 25 cm long and with 350 turns produce a magnetic field within it equal to the Earth's magnetic field (5.0 × 10-5 T). What current is required?
A solenoid that is 72 cm long produces a magnetic field of 1.8 T within its core when it carries a current of 8.1 A. How many turns of wire are contained in this solenoid?
The maximum current in a superconducting solenoid can be as large as 3.75 kA. If the number of turns per meter in such a solenoid is 3650, what is the magnitude of the magnetic field it produces?
To construct a solenoid, you wrap insulated wire uniformly around a plastic tube 7.6 cm in diameter and 33 cm in length. You would like a 3.0-A current to produce a 2.5-kG magnetic field inside your solenoid. What is the total length of wire you will need to meet these specifications?
An electron moves at right angles to a magnetic field of 0.23 T. What is its speed if the force exerted on it is 8.9 × 10-15 N?
A proton is to orbit the Earth at the equator using the Earth's magnetic field to supply part of the necessary centripetal force. Should the proton move eastward or westward? Explain.
Figure 22-52 shows an electron beam whose initial direction of motion is horizontal, from right to left. A magnetic field deflects the beam downward. What is the direction of the magnetic field?Figure 22-52
The three wires shown in FIGURE 22-53 are long and straight, and they each carry a current of the same magnitude, I. The currents in wires 1 and 3 are out of the page; the current in wire 2 is into the page. What is the direction of the magnetic force experienced by wire 3?Figure 22-53
Each of the current-carrying wires in Figure 22-53 is long and straight, and carries the current I either into or out of the page, as shown. What is the direction of the net magnetic field produced by these three wires at the center of the triangle?Figure 22-53
The four wires shown in FIGURE 22-54 are long and straight, and they each carry a current of the same magnitude, I. The currents in wires 1, 2, and 3 are out of the page; the current in wire 4 is into the page. What is the direction of the magnetic force experienced by wire 2?Figure 22-54
Each of the current-carrying wires in Figure 22-54 is long and straight, and carries the current I either into or out of the page, as shown. What is the direction of the net magnetic field produced by these four wires at the center of the square?Figure 22-54
Experiments have shown that thought processes in the brain can be affected if the parietal lobe is exposed to a magnetic field with a strength of 1.0 T. How much current must a long, straight wire carry if it is to produce a 1.0-T magnetic field at a distance of 0.50 m? (For comparison, a typical
Experiments carried out on the television show Mythbusters determined that a magnetic field of 1000 gauss is needed to corrupt the information on a credit card's magnetic strip. (They also busted the myth that a credit card can be demagnetized by an electric eel or an eelskin wallet.) Suppose a
Cryomagnetics, Inc., advertises a highfield, superconducting solenoid that produces a magnetic field of 17 T with a current of 105 A. What is the number of turns per meter in this solenoid?
Consider a current loop immersed in a magnetic field, as in Figure 22-47 (a). It is given that B = 0.42 T and I = 8.8 A. In addition, the loop is a square 0.38 m on a side. Find the magnitude of the magnetic force exerted on each side of the loop.Figure 22-47
A negatively charged ion moves due north with a speed of 1.5 × 106 m/s at the Earth's equator. What is the magnetic force exerted on this ion?
A positively charged particle moves through a region with a uniform electric field pointing toward the top of the page and a uniform magnetic field pointing into the page. The particle can have one of the four velocities shown in FIGURE 22-55.(a) Rank the four possibilities in order of increasing
A proton follows the path shown in FIGURE 22-56 as it moves through three regions with different uniform magnetic fields, B1, B2, and B3. In each region the proton completes a half-circle, and the magnetic field is perpendicular to the page.(a) Rank the three fields in order of increasing
Suppose the initial speed of the proton in Figure 22-56 is increased.(a) Does the radius of each half-circular path segment increase, decrease, or stay the same?(b) Choose the best explanation from among the following:I. The radius of a circular orbit in a magnetic field is proportional to the
An MRI (magnetic resonance imaging) solenoid produces a magnetic field of 1.5 T. The solenoid is 2.5 m long, 1.0 m in diameter, and wound with insulated wires 2.2 mm in diameter. Find the current that flows in the solenoid. (Your answer should be rather large.)
A long, straight wire carries a current of 14 A. Next to the wire is a square loop with sides 1.0 m in length, as shown in FIGURE 22-57. The loop carries a current of 2.5 A in the direction indicated.(a) What is the direction of the net force exerted on the loop? Explain.(b) Calculate the magnitude
A particle with a charge of 38 µC moves with a speed of 77 m/s in the positive x direction. The magnetic field in this region of space has a component of 0.45 T in the positive y direction, and a component of 0.85 T in the positive z direction. What are the magnitude and direction of the magnetic
A beam of protons with various speeds is directed in the positive x direction. The beam enters a region with a uniform magnetic field of magnitude 0.52 T pointing in the negative z direction, as indicated in FIGURE 22-58. It is desired to use a uniform electric field (in addition to the magnetic
Two parallel wires, each carrying a current of 2.2 A in the same direction, are shown in FIGURE 22-59. Find the direction and magnitude of the net magnetic field at points A, B, and C.
Repeat Problem 77 for the case where the current in wire 1 is reversed in direction.Problem 77Two parallel wires, each carrying a current of 2.2 A in the same direction, are shown in FIGURE 22-59. Find the direction and magnitude of the net magnetic field at points A, B, and C.
A current of 2.4 A flows through a circular coil of wire with 52 turns and a radius of 0.64 cm. The coil rotates in a uniform 0.12-T magnetic field.(a) What is the maximum torque exerted on the loop of wire?(b) The time-averaged torque on the loop is half its maximum value. If the moment of inertia
A proton high above the equator approaches the Earth moving straight downward with a speed of 375 m/s. Find the acceleration of the proton, given that the magnetic field at its altitude is 4.05 × 10-5T.
A student wishes to suspend a square loop of wire at a 45° angle to the vertical using the Earth's magnetic field. The geometry is depicted in FIGURE 22-60. At the student's location the Earth's magnetic field has a magnitude of 5.2 × 10-5 T and is oriented 60.0° below horizontal. All of
A powerful bolt of lightning can carry a current of 225 kA.(a) Treating a lightning bolt as a long, thin wire, calculate the magnitude of the magnetic field produced by such a bolt of lightning at a distance of 35 m.(b) If two such bolts strike simultaneously at a distance of 35 m from each other,
Consider the two current-carrying wires shown in FIGURE 22-61. The current in wire 1 is 3.7 A; the current in wire 2 is adjusted to make the net magnetic field at point A equal to zero.(a) Is the magnitude of the current in wire 2 greater than, less than, or the same as that in wire 1? Explain.(b)
The astronomical object 4U014 + 61 has the distinction of creating the most powerful magnetic field ever observed. This object is referred to as a "magnetar" (a subclass of pulsars), and its magnetic field is 1.3 × 1015 times greater than the Earth's magnetic field.(a) Suppose a 2.5-m straight
Consider a system consisting of two concentric solenoids, as illustrated in FIGURE 22-62. The current in the outer solenoid is I1 = 1.25 A, and the current in the inner solenoid is I2 = 2.17 A. Given that the number of turns per centimeter is 105 for the outer solenoid and 125 for the inner
Solenoids produce magnetic fields that are relatively intense for the amount of current they carry. To make a direct comparison, consider a solenoid with 48.0 turns per centimeter, a radius of 1.27 cm, and a current of 0.776 A.(a) Find the magnetic field at the center of the solenoid.(b) What
The current in a solenoid with 28 turns per centimeter is 0.55 A. The solenoid has a radius of 1.5 cm. A long, straight wire runs along the axis of the solenoid, carrying a current of 16 A. Find the magnitude of the net magnetic field a radial distance of 0.75 cm from the straight wire.
One way to study brain function is to produce a rapidly changing magnetic field within the brain. When this technique, known as transcranial magnetic stimulation (TMS), is applied to the prefrontal cortex, for example, it can reduce a person's ability to conjugate verbs, though other thought
In one portion of a synchrotron undulator, electrons traveling at 2.99 × 108 m/s enter a region of uniform magnetic field with a strength of 0.844 T.(a) What is the acceleration of an electron in this region?(b) The total power of X-rays emitted by these electrons is given by P = (1.07 × 10-45)a2
A single current- carrying circular loop of radius R is placed next to a long, straight wire, as shown in FIGURE 22-63. The current in the wire points to the right and is of magnitude I. (a) In which direction must current flow in the loop to produce zero magnetic field at its center?
A 0.32-mC particle moves with a speed of 16 m/s through a region where the magnetic field has a strength of 0.95 T. At what angle to the field is the particle moving if the force exerted on it is(a) 4.8 × 10-6 N,(b) 3.0 × 10-6 N,(c) 1.0 × 10-7 N?
A thin ring of radius R and charge per length l rotates with an angular speed ω about an axis perpendicular to its plane and passing through its center. Find the magnitude of the magnetic field at the center of the ring.
A solenoid is made from a 25-m length of wire of resistivity 2.3 × 10-8 Ω • m. The wire, whose radius is 2.1 mm, is wrapped uniformly onto a plastic tube 4.5 cm in diameter and 1.65 m long. Find the emf to which the ends of the wire must be connected to produce a magnetic field of 0.015 T
In the Bohr model of the hydrogen atom, the electron moves in a circular orbit of radius 5.29 × 10-11 m about the nucleus. Given that the charge on the electron is -1.60 × 10-19 C, and that its speed is 2.2 × 106 m/s, find the magnitude of the magnetic field the electron produces at the nucleus
A single-turn square loop carries a current of 18 A. The loop is 15 cm on a side and has a mass of 0.035 kg. Initially the loop lies flat on a horizontal tabletop. When a horizontal magnetic field is turned on, it is found that only one side of the loop experiences an upward force. Find the minimum
Approximating a neuron by a straight wire, what electric current is needed to produce a magnetic field of 1.0 * 10-15 T at a distance of 5.0 cm?A. 4.0 × 10-22 AB. 7.9 × 10-11 AC. 2.5 × 10-10 AD. 1.0 × 10-7 A
Suppose a neuron in the brain carries a current of 5.0 × 10-8 A. Treating the neuron as a straight wire, what is the magnetic field it produces at a distance of 7.5 cm?A. 1.3 × 10-13 TB. 4.2 × 10-12 TC. 1.1 × 10-10 TD. 3.3 × 10-7 T
A given neuron in the brain carries a current of 3.1 × 10-8 A. If the SQUID detects a magnetic field of 2.8 × 10-14 T, how far away is the neuron? Treat the neuron as a straight wire.A. 22 cmB. 70 cmC. 140 cmD. 176 cm
A SQUID detects a magnetic field of 1.8 × 10-14 T at a distance of 13 cm. How many electrons flow through the neuron per second? Treat the neuron as a straight wire.A. 1.2 × 1010B. 2.3 × 1010C. 7.3 × 1010D. 9.2 × 1010
Suppose the speed of the isotopes is doubled.(a) Does the separation distance, d, increase, decrease, or stay the same? Explain.(b) Find the separation distance for this case.
Suppose we change the initial speed of 238U, leaving everything else the same.(a) If we want the separation distance to be zero, should the initial speed of 238U be increased or decreased? Explain.(b) Find the required initial speed.
You would like to store 9.9 J of energy in the magnetic field of a solenoid. The solenoid has 580 circular turns of diameter 7.2 cm distributed uniformly along its 28-cm length.(a) How much current is needed?(b) What is the magnitude of the magnetic field inside the solenoid?(c) What is the energy
Transformer 1 has a primary voltage Vp and a secondary voltage Vs. Transformer 2 has twice the number of turns on both its primary and secondary coils compared with transformer 1. If the primary voltage on transformer 2 is 2Vp, what is its secondary voltage? Explain.
The electric motor in a toy train requires a voltage of 4.5 V. Find the ratio of turns on the primary coil to turns on the secondary coil in a transformer that will step the 120-V household voltage down to 4.5 V.
A disk drive plugged into a 120-V outlet operates on a voltage of 9.0 V. The transformer that powers the disk drive has 125 turns on its primary coil.(a) Should the number of turns on the secondary coil be greater than or less than 125? Explain.(b) Find the number of turns on the secondary coil.
A solenoid with 385 turns per meter and a diameter of 17.0 cm has a magnetic flux through its core of magnitude 1.28 × 10-4 T • m2.(a) Find the current in this solenoid.(b) How would your answer to part (a) change if the diameter of the solenoid were doubled? Explain.
A transformer with a turns ratio (secondary/primary) of 1:18 is used to step down the voltage from a 120-V wall socket to be used in a battery recharging unit. What is the voltage supplied to the recharger?
A neon sign that requires a voltage of 11,000 V is plugged into a 120-V wall outlet. What turns ratio (secondary/primary) must a transformer have to power the sign?
A step-down transformer produces a voltage of 6.0 V across the secondary coil when the voltage across the primary coil is 120 V. What voltage appears across the primary coil of this transformer if 120 V is applied to the secondary coil?
A step-up transformer has 30 turns on the primary coil and 750 turns on the secondary coil. If this transformer is to produce an output of 4800 V with a 15-mA current, what input current and voltage are needed?
An airplane flies level to the ground toward the north pole. (a) Is the induced emf from wing tip to wing tip when the plane is at the equator greater than, less than, or equal to the wing-tip-to-wing-tip emf when it is at the latitude of New York? (b) Choose the best explanation from
You hold a circular loop of wire at the north magnetic pole of the Earth. Consider the magnetic flux through this loop due to the Earth's magnetic field. Is the flux when the normal to the loop points horizontally greater than, less than, or equal to the flux when the normal points vertically
The inductor shown in FIGURE 23-47 is connected to an electric circuit with a changing current. At the moment in question, the inductor has an induced emf with the indicated direction. Is the current in the circuit at this time increasing and to the right, increasing and to the left, decreasing and
The Voyager I spacecraft moves through interstellar space with a speed of 8.0 × 103 m/s. The magnetic field in this region of space has a magnitude of 2.0 × 10-10 T. Assuming that the 5.0-m-long antenna on the spacecraft is at right angles to the magnetic field, find the induced emf between its
The coils used to measure the movements of a blowfly, as described in Section 23-5, have a diameter of 2.0 mm. In addition, the fly is immersed in a magnetic field of magnitude 0.15 mT. Find the maximum magnetic flux experienced by one of these coils.
Computerized jaw tracking, or electrognathography (EGN), is an important tool for diagnosing and treating temporomandibular disorders (TMDs) that affect a person's ability to bite effectively. The first step in applying EGN is to attach a small permanent magnet to the patient's gum below the lower
A single-turn square loop of side L is centered on the axis of a long solenoid. In addition, the plane of the square loop is perpendicular to the axis of the solenoid. The solenoid has 1250 turns per meter and a diameter of 6.00 cm, and carries a current of 2.50 A. Find the magnetic flux through
A rectangular loop of wire 24 cm by 72 cm is bent into an L shape, as shown in FIGURE 23-49. The magnetic field in the vicinity of the loop has a magnitude of 0.035 T and points in a direction 25° below the y axis. The magnetic field has no x component. Find the magnitude of the magnetic flux
Consider a rectangular loop of wire 6.8 cm by 9.2 cm in a uniform magnetic field of magnitude 1.7 T. The loop is rotated from a position of zero magnetic flux to a position of maximum flux in 21 ms. What is the average induced emf in the loop?
A car with a vertical radio antenna 85 cm long drives due east at 25 m/s. The Earth's magnetic field at this location has a magnitude of 5.9 × 10-5 T and points northward,72° below the horizontal.(a) Is the top or the bottom of the antenna at the higher potential? Explain.(b) Find the induced emf
The rectangular coils in a 355-turn generator are 13 cm by 19 cm. What is the maximum emf produced by this generator when it rotates with an angular speed of 505 rpm in a magnetic field of 0.55 T?
A cubical box 22 cm on a side is placed in a uniform 0.35-T magnetic field. Find the net magnetic flux through the box.
An MRI scanner is based on a solenoid magnet that produces a large magnetic field. The magnetic field doesn't stop at the solenoid's edge, however, but extends into the area around the magnet. Suppose a technician walks toward the scanner at 0.80 m/s from a region 1.0 m from the scanner where the
Transcranial magnetic stimulation (TMS) is a noninvasive method for studying brain function, and possibly for treatment as well. In this technique, a conducting loop is held near a person's head, as shown in FIGURE 23-50. When the current in the loop is changed rapidly, the magnetic field it
A magnetic field with the time dependence shown in FIGURE 23- 51 is at right angles to a 155-turn circular coil with a diameter of 3.75 cm. What is the induced emf in the coil at (a) T = 2.50 ms, (b) T = 7.50 ms, (c) T = 15.0 ms, and (d) T = 25.0 ms?FIGURE 23- 51
The characteristic time of an RL circuit with L = 25 mH is twice the characteristic time of an RC circuit with C = 45 µF. Both circuits have the same resistance R. Find (a) the value of R and (b) the characteristic time of the RL circuit.
A 6.0-V battery is connected in series with a 49-mH inductor, a 150-Ω resistor, and an open switch. (a) At what time after the switch is closed (t = 0) will the current in the circuit be equal to 12 mA? (b) How much energy is stored in the inductor when the current reaches its maximum
A bar magnet is inside a closed cubical box. Magnetic field lines pointing outward from the box produce positive flux, and those pointing inward produce negative magnetic flux. (a) Is the total magnetic flux through the surface of the box positive, negative, or zero? (b) Choose the best
A 9.0-V battery is connected in series with a 31-mH inductor, a 180-Ω resistor, and an open switch. (a) What is the current in the circuit 0.120 ms after the switch is closed? (b) How much energy is stored in the inductor at this time?
Suppose the fly described in Problem 78 turns through an angle of 90° in 37 ms. If the magnetic flux through one of the coils on the insect goes from a maximum to zero during this maneuver, and the coil has 85 turns of wire, find the magnitude of the induced emf.
A conducting rod of mass m is in contact with two vertical conducting rails separated by a distance L, as shown in FIGURE 23-52. The entire system is immersed in a magnetic field of magnitude B pointing out of the page. Assuming the rod slides without friction, (a) Describe the motion of the
A single-turn rectangular loop of width W and length L moves parallel to its length with a speed v. The loop moves from a region with a magnetic field B(vector) perpendicular to the plane of the loop to a region where the magnetic field is zero, as shown in FIGURE 23-53. Find the rate of change in
The switch in the circuit shown in FIGURE 23-54 is open initially.(a) Find the current in the circuit a long time after the switch is closed.(b) Describe the behavior of the lightbulb from the time the switch is closed until the current reaches the value found in part (a).(c) Now, suppose the
An electric field E and a magnetic field B have the same energy density.(a) Express the ratio E / B in terms of the fundamental constants ε0 and µ0.(b) Evaluate E / B numerically, and compare your result with the speed of light.
Suppose the downward vertical component of the magnetic field increases as a car drives over a loop detector. As viewed from above, is the induced current in the loop clockwise, counterclockwise, or zero?
A car drives onto a loop detector and increases the downward component of the magnetic field within the loop from 1.2 × 10-5 T to 2.6 × 10-5 T in 0.38 s. What is the induced emf in the detector if it is circular, has a radius of 0.67 m, and consists of four loops of wire?A. 0.66 × 10-4 VB. 1.5 *
A truck drives onto a loop detector and increases the downward component of the magnetic field within the loop from 1.2 × 10-5 T to the larger value B in 0.38 s. The detector is circular, has a radius of 0.67 m, and consists of three loops of wire. What is B, given that the induced emf is 8.1 ×
Suppose a motorcycle increases the downward component of the magnetic field within a loop only from 1.2 × 10-5 T to 1.9 × 10-5 T. The detector is square, is 0.75 m on a side, and has four loops of wire. Over what period of time must the magnetic field increase if it is to induce an emf of 1.4 ×
A metal ring with a break in its perimeter is dropped from a field free region of space into a region with a magnetic field. What effect does the magnetic field have on the ring?
Figure 23-29 shows a vertical iron rod with a wire coil of many turns wrapped around its base. A metal ring slides over the rod and rests on the wire coil. Initially the switch connecting the coil to a battery is open, but when it is closed, the ring flies into the air. Explain why this
Recently, NASA tested a power generation system that involves connecting a small satellite to the space shuttle with a conducting wire several miles long. Explain how such a system can generate electrical power.
A 0.085-T magnetic field passes through a circular ring of radius 4.1 cm at an angle of 22° with the normal. Find the magnitude of the magnetic flux through the ring.
A 0.65-T magnetic field is perpendicular to a circular loop of wire with 73 turns and a radius of 18 cm. If the magnetic field is reduced to zero in 0.12 s, what is the magnitude of the induced emf?
Suppose the ring is initially to the left of the field region, where there is no field, and is moving to the right. When the ring is partway into the field region, (a) Is the induced current in the ring clockwise, counterclockwise, or zero, and (b) Is the magnetic force exerted on the
Suppose the ring is completely inside the field region initially and is moving to the right.(a) Is the induced current in the ring clockwise, counterclockwise, or zero, and (b) Is the magnetic force on the ring to the right, to the left, or zero? Explain. The ring now begins to emerge from the
REFERRING TO EXAMPLE 23-8 (a) What external force is required to give the rod a speed of 3.49 m/s, everything else remaining the same? (b) What is the current in the circuit in this case?
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