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Holt Physics

Raymond A. Serway, Jerry S. Faughn

Chapter 21

Magnetism - all with Video Answers

Educators

Chapter Questions

05:45

Problem 1

What is the minimum number of poles for a magnet?

Daniel Azubuike
Daniel Azubuike
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01:00

Problem 2

When you break a magnet in half, how many poles does each piece have?

Jheremiah Simon
Jheremiah Simon
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00:33

Problem 3

The north pole of a magnet is attracted to the geo graphic North Pole of Earth, yet like poles repel. Can you explain this?

Suzanne W.
Suzanne W.
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02:19

Problem 4

Which way would a compass needle point if you were at the magnetic north pole?

Jheremiah Simon
Jheremiah Simon
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01:10

Problem 5

You are an astronaut stranded on a planet with no test equipment or minerals around. The planet does not even have a magnetic field You have two iron bars in your possession; one is magnetized, one is not. How can you determine which one is magnetized?

Suzanne W.
Suzanne W.
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01:39

Problem 6

In Figure $21-17$, two permanent magnets with holes bored through their centers are placed one over the other, Because the poles of the upper magnet are the reverse of those of the lower, the upper magnet levitates above the lower magnet. If the upper magnet were displaced slightly, either up or down, would the resulting motion be periodic? Explain. What would happen if the upper magnet were inverted?

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Suzanne W.
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00:37

Problem 7

What is a magnetic domain?

Salamat Ali
Salamat Ali
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02:30

Problem 8

Why are iron atoms so strongly affected by magnetic fields?

Jheremiah Simon
Jheremiah Simon
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05:53

Problem 9

When a magnetized steel needle is strongly heated in a Bunsen burner flame, it becomes demagnetized. Explain why.

Daniel Azubuike
Daniel Azubuike
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00:20

Problem 10

What indicates that a piece of iron is magnetic, its attraction to or repulsion from another piece of iron?

Suzanne W.
Suzanne W.
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00:30

Problem 11

Why does a very strong magnet attract both poles of a weak magnet?

Suzanne W.
Suzanne W.
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00:43

Problem 12

A magnet attracts a piece of iron. The iron can then attract another piece of iron. Explain, on the basis of alignment of domains, what happens in each piece of iron.

Suzanne W.
Suzanne W.
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00:28

Problem 13

When a small magnet is repeatedly dropped, it becomes demagnetized. Explain what happens to the magnet sub-atomically.

Suzanne W.
Suzanne W.
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01:05

Problem 14

A conductor carrying a current is arranged so that electrons flow in one segment from east to west. If a compass is held over this segment of the wire, in what direction is the needle deflected?

Suzanne W.
Suzanne W.
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00:47

Problem 15

What factors does the strength of the magnetic field of a solenoid depend on?

Suzanne W.
Suzanne W.
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00:53

Problem 16

A solenoid with ends marked $A$ and $B$ is suspended by a thread so that the core can rotate in the horizontal plane. A current is maintained in the coil so that the electrons move clockwise when viewed from end $A$ toward end $B$. How will the coil align itself in Earth's magnetic field?

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Suzanne W.
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00:37

Problem 17

Is it possible to orient a current-carrying loop of wire in a uniform magnetic field so that the loop will not tend to rotate?

Suzanne W.
Suzanne W.
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00:53

Problem 18

If a solenoid were suspended by a string so that it could rotate freely, could it be used as a compass when it carried a direct current? Could it also be used if the current were alternating in direction?

Suzanne W.
Suzanne W.
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00:38

Problem 19

Two charged particles are projected into a region where there is a magnetic field perpendicular to their velocities. If the particles are deflected in opposite directions, what can you say about them?

Suzanne W.
Suzanne W.
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00:41

Problem 20

Suppose an electron is chasing a proton up this page when suddenly a magnetic field pointing into the page is applicd. What would happen to the particles?

Suzanne W.
Suzanne W.
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00:40

Problem 21

Why does the picture on a television screen become distorted when a magnet is brought near the screen?

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Suzanne W.
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01:27

Problem 22

A proton moving horizontally enters a region where there is a uniform magnetic field perpendicular to the proton's velocity, as shown in Figure $21-18$. Describe the proton's subsequent motion. How would an electron behave under the same circumstances?

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00:40

Problem 23

Explain why two parallel wires carrying currents in opposite directions repel each other.

Suzanne W.
Suzanne W.
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00:49

Problem 24

Can a stationary magnetic field set a resting electron in motion? Explain.

Suzanne W.
Suzanne W.
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06:39

Problem 25

At a given instant, a proton moves in the positive $x$ direction in a region where there is a magnetic field in the negative $z$ direction. What is the direction of the magnetic force? Does the proton continue to move along the $x$ -axis? Explain.

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Daniel Azubuike
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02:03

Problem 26

Find the direction of the magnetic field for a positively charged particle moving in each situation in Figure $21-19$ if the direction of the magnetic force acting on it is as indicated.

Suzanne W.
Suzanne W.
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01:32

Problem 27

A stream of electrons is projected horizontally to the right. A straight conductor carrying a current is supported parallel to and above the electron stream.
a. What is the effect on the electron stream if the current in the conductor is left to right?
b. What is the effect if the current is reversed?

Suzanne W.
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00:52

Problem 28

If the conductor in item 27 is replaced by a magnet with a downward magnetic field, what is the effect on the electron stream?

Suzanne W.
Suzanne W.
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00:32

Problem 29

Two wires carrying equal but opposite currents are twisted together in the construction of a circuit. Why does this technique reduce stray magnetic fields?

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Suzanne W.
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01:26

Problem 30

A duck flying due east passes over Atlanta, where the magnetic field of the Earth is $5.0 \times 10^{-5} \mathrm{T}$ directed north. The duck has a positive charge of $4.0 \times 10^{-8} \mathrm{C}$ If the magnetic force acting on the duck is $3.0 \times 10^{-11} \mathrm{N}$ upward, what is the duck's velocity?

Suzanne W.
Suzanne W.
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02:26

Problem 31

A proton moves eastward in the plane of Earth's magnetic equator so that its distance from the ground remains constant. What is the speed of the proton if Earth's magnetic field points north and has a magnitude of $5.0 \times 10^{-5} \mathrm{T}$

Suzanne W.
Suzanne W.
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02:43

Problem 32

A wire carries a 10.0 A current at an angle $90.0^{\circ}$ from the direction of a magnetic field. If the magnitude of the magnetic force on a 5.00 m length of the wire is $15.0 \mathrm{N}$, what is the strength of the magnetic field?

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02:50

Problem 33

A thin $1.00 \mathrm{m}$ long copper rod in a uniform magnetic field has a mass of $50.0 \mathrm{g}$. When the rod carries a current of $0.245 \mathrm{A}$, it floats in the magnetic field. What is the field strength of the magnetic field?

Suzanne W.
Suzanne W.
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03:02

Problem 34

A proton moves at $2.50 \times 10^{6} \mathrm{m} / \mathrm{s}$ horizontally at a right angle to a magnetic field.
a. What is the strength of the magnetic field required to exactly balance the weight of the proton and keep it moving horizontally!
b. Should the direction of the magnetic field be in a horizontal or a vertical plane?

Suzanne W.
Suzanne W.
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02:12

Problem 35

Find the direction of the force on a proton moving through each magnetic field in Figure $21-20$.

Suzanne W.
Suzanne W.
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01:59

Problem 36

Find the direction of the force on an electron moving through each magnetic field in Figure $21-20$

Suzanne W.
Suzanne W.
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01:05

Problem 37

In Figure $21-20$, assume that in each case the velocity vector shown is replaced with a wire carrying a current in the direction of the velocity vector. Find the direction of the magnetic force acting on each wire.

Suzanne W.
Suzanne W.
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02:00

Problem 38

A proton moves at a speed of $2.0 \times 10^{7} \mathrm{m} / \mathrm{s}$ at right angles to a magnetic field with a magnitude of $0.10 \mathrm{T}$. Find the magnitude of the acceleration of the proton.

Suzanne W.
Suzanne W.
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16:54

Problem 39

A proton moves perpendicularly to a uniform magnetic field, $\mathbf{B}$, with a speed of $1.0 \times 10^{7} \mathrm{m} / \mathrm{s}$ and experiences an acceleration of $2.0 \times 10^{13} \mathrm{m} / \mathrm{s}^{2}$ in the positive $x$ direction when its velocity is in the positive $z$ direction. Determine the magnitude and direction of the field.

Daniel Azubuike
Daniel Azubuike
Numerade Educator
03:27

Problem 40

A proton travels with a speed of $3.0 \times 10^{6} \mathrm{m} / \mathrm{s}$ at an angle of $37^{\circ}$ west of north. A magnetic field of
$0.30 \mathrm{T}$ points to the north. Determine the following
a. the magnitude of the magnetic force on the proton
b. the direction of the magnetic force on the proton
c. the proton's acceleration as it moves through the magnetic field
(Hint: The magnetic force experienced by the pro. ton in the magnetic field is proportional to the component of the proton's velocity that is perpendicular to the magnetic field.

Suzanne W.
Suzanne W.
Numerade Educator
02:34

Problem 41

In Figure $21-21,$ a $15 \mathrm{cm}$ length of conducting wire that is free to move is held in place between two thin conducting wires. All the wires are in a magnetic field. When a $5.0 \mathrm{A}$ current is in the wire, as shown in the figure, the wire segment moves upward at a constant velocity. Assuming the wire slides without friction on the two vertical conductors and has a mass of $0.15 \mathrm{kg}$, find the magnitude and direction of the minimum magnetic field that is required to move the wire.

Suzanne W.
Suzanne W.
Numerade Educator
02:33

Problem 42

A current, $I=15 \mathrm{A},$ is directed along the positive $x$ -axis and perpendicular to a uniform magnetic field, The conductor experiences a magnetic force per unit length of $0.12 \mathrm{N} / \mathrm{m}$ in the negative $y$ direction. Calculate the magnitude and direction of the magnetic field in the region through which the current passes.

Jheremiah Simon
Jheremiah Simon
Numerade Educator
03:09

Problem 43

A proton moves in a circular path perpendicular to a constant magnetic field so that the proton takes $1.00 \times 10^{-6} \mathrm{s}$ to complete one revolution, Determine the strength of the constant magnetic field (Hint: The magnetic force exerted on the proton is the force that maintains circular motion, and the number of radians per time interval is the angular speed

Suzanne W.
Suzanne W.
Numerade Educator
02:30

Problem 44

A singly charged positive ion that has a mass of $6.68 \times 10^{-27} \mathrm{kg}$ moves clockwise with a speed of $1.00 \times 10^{4} \mathrm{m} / \mathrm{s} .$ The positively-charged ion moves in a circular path that has a radius of $3.00 \mathrm{cm}$. Find the direction and strength of the uniform magnetic field. (Hint: The magnetic force exerted on the positive ion is the force that maintains circular motion, and the speed given for the positive ion is its tangential speed.)

Suzanne W.
Suzanne W.
Numerade Educator