Chapter 24 Physics- Magnetism

galvanometer

A sensitive current-indicating instrument is called a

An electron beam passing perpendicularly through a magnetic field is deflected. If the beam were instead composed of protons, the beam would be deflected A. in the opposite direction. B. opposite to the magnetic field direction. C. parallel to and with the magnetic field. D. in the same direction. E. not at all-non-existent.

A. in the opposite direction

A galvanometer best makes use of the fact that there exists a magnetic field A. about aligned magnetic domains. B. about a current-carrying wire. C. about a pivoted compass needle. D. wherever a change of voltage occurs. E. between the poles of a U-shaped magnet.

B. about a current-carrying wire.

Which force field can accelerate an electron, but never change its speed? A. electric field B. magnetic field C. both of these D. none of these

B. magnetic field

An iron rod becomes magnetic when A. its atoms are aligned. B. the net spins of many of its electrons are aligned. C. its electrons stop moving and point in the same direction. D. opposite ions accumulate at each end. E. none of the above

B. the net spins of many of its electrons are aligned.

Which of the following are creatures that are known to harbor tiny magnets within their bodies?

Bacteria, pigeons, bees, wasps, monarch butterflies, and sea turtles

Why is every piece of iron not a magnet? Because they have no magnetic poles Because electrons are not aligned Because they have no domains Because the domains in ordinary iron are not aligned

Because the domains in ordinary iron are not aligned

What does a common bar magnet have in common with an electromagnet?

Both have the same source—the motion of electric charge.

If a steady magnetic field exerts a force on a moving charge, that force is directed A. in the direction of the motion. B. opposite the motion. C. at right angles to the direction of the motion.

C. at right angles to the direction of the motion.

Which force field can accelerate an electron? A. magnetic field B. electric field C. both of these D. neither of these

C. both of these

Define a magnetic domain. Clusters of atoms with only north poles Clusters of atoms with their magnetic fields not aligned Clusters of atoms where every atom has an opposing magnetic field Clusters of atoms with their magnetic fields aligned

Clusters of atoms with their magnetic fields aligned

The source of all magnetism is A. tiny pieces of iron. B. tiny domains of aligned atoms. C. ferromagnetic materials. D. moving electric charge. E. none of these

D. moving electric charge

The shape of a magnetic field about a current carrying wire is much the same as the shape of an electric field A. between the plates of a charged capacitor. B. about a point electric charge. C. between two opposite point charges. D. None of these. E. All of these.

D. none of these

induced magnets

Domains in the unmagnetized piece of iron are induced into alignment by the magnetic field of the nearby magnet

Which of these cities has the smallest incidence of cosmic rays? A. New York City. B. Anchorage. C. All about the same. D. East Lansing, MI. E. Singapore.

E. Singapore

What is the source of the magnetic force? Magnetic poles in motion are the only source of magnetic forces. Spinning protons are the source of all magnetic forces. Electric charges in motion are the sources of magnetic forces. Stationary electrons are the source of magnetic forces.

Electric charges in motion are the sources of magnetic forces.

An electron beam is directed into a magnetic field. At what orientation to the magnetic field is the force on the beam greatest? Least?

Greatest magnetic force occurs when the electron beam and the magnetic field are perpendicular to each other, as depicted in Figure 24.13. When the beam and the field are parallel, no force is exerted on the beam.

Who discovered the relationship between electricity and magnetism, and in what setting?

Hans Christian Oersted in a classroom demonstration

What is the major similarity between a galvanometer and a simple electric motor? What is the major difference?

In both, coils are positioned in a magnetic field. A force produces rotation when current passes through the coils. The major difference is that the maximum rotation of the coil in a galvanometer is one half-turn, whereas, in a motor, the coil (wrapped on an armature) rotates through many complete turns—accomplished by alternating the current with each half-turn of the armature.

How does the compass app on your phone work??

Just like a regular compass it measures the Earth's magnetic field. Instead of a permanent magnet is uses a magnetometer to do this.

In what way is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles?

Like poles repel, unlike poles attract, and the force is proportional to the inverse square of the distance between two poles.

At what orientation in a magnetic field is the force greatest on a current-carrying wire? The least?

Like the electron beam in a magnetic field, greatest magnetic force occurs when the magnetic field and wire are perpendicular to each other. The least force—zero—occurs when the two are parallel.

An electric field about a point charge in free space is depicted by straight lines emanating from the charge (Chapter 23). By contrast, what is the shape of magnetic field lines about a current-carrying wire?

Magnetic field lines about a current-carrying wire form concentric circles (as shown in Figure 24.10a).

What law of physics tells you that if a current-carrying wire produces a force on a magnet, then a magnet must produce a force on a current-carrying wire?

Newton's third law, which applies to all forces in nature.

Do both electrical forces and magnetic forces depend on motion?

Only the magnetic force requires motion. Read on.

In what direction relative to a magnetic field does a moving charged particle experience maximum deflecting force? Minimum deflecting force? Parallel for maximum force, antiparallel for minimum force Perpendicular for maximum force, parallel for minimum force Perpendicular for minimum force, parallel for maximum force Parallel for minimum force, antiparallel for maximum force

Perpendicular for maximum force, parallel for minimum force

Yes, like so many things in the world, Earth's magnetic field varies with time.

Readings increase with altitude. Pilots encounter much more radiation than do people on the ground who are shielded by the atmosphere

What is the cause of the aurora borealis (the northern lights)?

The Earth's magnetic field guides trapped charged particles to follow field lines toward the poles, where they collide with the atmosphere, causing a glow.

If the motion of electric charges produces magnetism, where is this motion in a common bar magnet?

The answer is, in the electrons of the atoms that make up the magnet. These electrons are in constant motion. Two kinds of electron motion contribute to magnetism: electron spin and electron revolution. Electrons spin about their own axes like tops, and they also revolve about the atomic nucleus. In most common magnets, electron spin is the chief contributor to magnetism

How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnet? The field strength is zero outside the magnet. The field strength does not depend on the spacing of the field lines. The field strength is stronger where the field lines are closer. The field strength is weaker where the field lines are closer.

The field strength is stronger where the field lines are closer.

Why is the magnetic field strength greater inside a current-carrying loop of wire than about a straight section of wire?

The magnetic field of each segment of wire in the loop, due to electrons moving in the wire, adds together inside the loop, thereby making the field become bunched-up.

What is the direction of the magnetic field about an electric current when the direction of the current is reversed? The magnetic field reverses direction at every point. A clockwise pattern of concentric circles becomes a counterclockwise pattern of concentric circles and vice versa. The magnetic field rotates through 90 degrees at every point. A clockwise pattern of concentric circles becomes a radial outward pattern, while a counterclockwise pattern becomes radially inward. The radial magnetic field reverses direction. Inward pointing fields become outward pointing and vice versa. The magnetic field parallel to the wire reverses direction, so fields parallel to the current become antiparallel and vice versa.

The magnetic field reverses direction at every point. A clockwise pattern of concentric circles becomes a counterclockwise pattern of concentric circles and vice versa.

What are magnetic pole reversals?

The poles of the Earth's magnetic field undergo reversals

The source of a gravitational field is mass. The source of an electrical field is electric charge. What is the source of a magnetic field?

The source of a magnetic field is moving electric charges, predominantly electrons that revolve, or spin, or travel through conductors. The motion of electric charge produces magnetism.

What happens to the shape of a wire that is part of a circuit with a battery when the switch is closed and the battery voltage is increased? The wire bends more than it did before. The wire becomes more horizontal; that is, the wire bends less. The shape does not change.

The wire bends more than it did before.

What happens to the shape of a wire that is part of a circuit with a battery when the switch is closed and the direction of the current is reversed in the wire? The wire will bend less, but in the same direction. The wire will bend the same amount but in the opposite direction. The wire will bend more, but in the same direction. The shape of the wire will not change.

The wire will bend the same amount but in the opposite direction

What happens when a switch is closed in a circuit that contains a battery and a wire that is placed between the poles of a magnet? The wire will fall under the force of gravity. Nothing happens. The wire will stay where it is. The wire will either bend up or down between the poles of the magnet due to the force of the magnetic field.

The wire will either bend up or down between the poles of the magnet due to the force of the magnetic field.

Biomagnetism

These buoyant aquatic bacteria cannot sense up and down by gravity. Instead, they orient themselves with Earth's magnetic field with their built-in "compass needles."

If you drop an iron magnet on a concrete sidewalk it will become a weaker magnet. Why?

Vibrations provide energy to randomize the magnetic directions of the domains.

couple

When the compass needle is not aligned with the magnetic field, the oppositely directed forces on the needle produce a pair of torques (called a couple) that twist the needle into alignment

What is a very important difference between electric charges and magnetic poles? Electric forces follow the inverse-square law. Magnetic poles attract opposite magnetic poles. Whereas electric charges can be isolated, magnetic poles cannot. One is magnetic, the other electric.

Whereas electric charges can be isolated, magnetic poles cannot.

Why cannot a wooden pencil become magnetized?

Wood has no magnetic domains. All permanent magnets contain magnetic domains.

Earth Science is typified by the notion of continual change. Can the same be said of Earth's magnetic field?

Yes, like so many things in the world, Earth's magnetic field varies with time.

Is it correct to say that an electric motor extends the physics that underlies a galvanometer? Why?

Yes. The deflection forces are the same, but the direction of current in the motor is reversed cyclically.

When a galvanometer is calibrated to read potential difference it becomes an ammeter. a voltmeter. none of the above an ohm meter.

a voltmeter. An ammeter measures electric current. A voltmeter measures voltage, another term for potential difference. An ohm meter measures ohms, the amount of electrical resistance. So calibration for potential difference means calibration for voltage

An iron bar magnet is given a slight electric charge. Surrounding the charged bar is a magnetic field. an electric field. a gravitational field. all of the above

all of the above. All! The bar magnet has a magnetic field around it. It has mass with a gravitational field around it. It is electrically charged, so surrounding it is an electric field. We see three kinds of force fields, hence answer (d).

If a compass is moved in a circle around a current-carrying wire, the needle will be pointing________. always to the wire in accord with the inverse-square law in random directions always tangent to the circle

always tangent to the circle

The magnetic field strength inside a current-carrying coil is greater when the coil encloses a vacuum. a wooden rod. an iron rod. a glass rod.

an iron rod. A magnetic field already exists within a current-carrying coil. When an iron rod is inserted into the coil, domains in the rod are set into alignment by the field already present in the loop. The two add, resulting in greater field strength—in a way that wood and glass, lacking magnetic domains, cannot do

An electric field ___ accelerate and accelerate a charged particle A magnetic field _______ accelerate but can accelerate a charged particle

can; cannot

The direction of magnetic field lines about a current-carrying wire both of these extend radially from the wire. circle the wire in closed loops. none of the above

circle around wire in closed loops . a current carrying wire creates closed loops of magnetic fields around it. Electric fields about point charges, in contrast, follow straight-line paths.

The magnetic field about a straight length of current-carrying wire is _________. similar to the shape of an electric field about a charged wire aligned from north to south poles in the wire circular in shape in accord with the inverse-square law

circular in shape

the _________of the magnetic field surrounding the current-carrying wire.

circular shape

Magnetic Fields Arise From a) the orbital motion of electrons around nuclei.​ b) the intrinsic spin of electrons.​ c) electrons flowing in wires.​ d) all of the above.

d) all of the above

Earth's magnetic field affects cosmic rays by absorbing them. none of the above deflecting them. slowing their speeds.

deflecting them. Cosmic rays, or energetic charged particles that zip from outer space are deflected from us by Earth's magnetic field, just as beams of electrons are deflected from their paths in a lab setting. The field doesn't slow or absorb them. Interestingly, some of these deflected particles get trapped in the Van Allen Belt.

A magnetic field is produced by the motion of ________

electric charge

What produces a magnetic field? Electric charges in motion Magnetic monopoles Electric dipoles Voltage

electric charges in motion

What type of field or fields surround a moving electron? Electric field only Electric field and magnetic field Magnetic field only No fields surround the charge

electric field and magnetic field

What kinds of appliances work on the principle of deflection of a current-carrying wire in a magnetic field? electric generator both an electric generator and an electric motor electric motor

electric motor

Two kinds of electron motion contribute to magnetism:

electric spin and electric revolution

compared to the huge force that attracts and iron tack to a strong magnet, the force that the tack exerts on the magnet is relatively small equally huge

equally huge

How can a magnet attract a piece of iron that is not magnetized?

induced magnets

What effect does Earth's magnetic field have on the intensity of cosmic rays striking Earth's surface? It reduces the intensity near the poles and increases it at the equator. It increases the intensity. It does not change the intensity. It reduces the intensity.

it reduces the intensity

how an aurora is formed

magentosphere , the region around Earth where charged particles from the solar wind are trapped in Van Allen belts. They spiral around the magnetic field lines. Near the poles, the van allen belts intersect the atmosphere. the charged particles collide with the atmosphere atoms and create an aurora

Into which stable force field can a proton be placed at rest without being accelerated? both of these Electric field. Magnetic field. none of the above

magnetic field. Being at rest is the key to this question. A proton (or electron) at rest experiences a force in an electric field, but not in a magnetic field. A proton (or electron) in motion DOES experience a force in a magnetic field, and a resulting acceleration—in both fields.

Compared with a simple galvanometer, an electric motor is _________. different in that it is a source of voltage much the same with small modifications a complicated voltmeter fundamentally different

much the same with small modifications

No magnetic force acts on a current carrying wire when it none of the above either or both of these carries a very small current. is perpendicular to the magnetic field.

none of the above. Magnetic force on a current-carrying wire depends on the orientation of the wire. When a current-carrying wire is perpendicular to the magnetic field, magnetic force is maximum. When parallel and aligned with the magnetic field, force is zero. Since this isn't an answer choice, none of the above is the correct response.

all magnets have a _______ and ______ pole

north and south

greatest force

particle movement in direction perpendicular to the magnetic field lines

less force

particle movement other than perpendicular to the magnetic field lines

no force

particle movement parallel to the magnetic field lines

The force that acts on a current-carrying wire placed in a magnetic field is _________. parallel in direction to the magnetic field perpendicular in direction to the magnetic field opposite in direction to the magnetic field perpendicular or parallel depending on the orientation of the field

perpendicular in direction to the magnetic field

The force that acts on an electron traveling in a magnetic field is _________. opposite in direction to the magnetic field perpendicular in direction to the magnetic field parallel in direction to the magnetic field perpendicular or parallel depending on the orientation of the field

perpendicular in direction to the magnetic field

The _______ may well be able to sense direction because of a built-in magnetic "compass" within its skull.

pigeon

If a magnet produces a force on a current-carrying wire, the wire none of these may produce a force on the magnet. produces a force on the magnet. is likely warmed.

produces a force on the magnet. Newton's third law is a foundation for all branches of physics, pure and simple. Recall that for every applied force there is always an equal and opposite reaction force. Magnet pushes on wire: Wire pushes on magnet. For sure, not may.

The magnetic field about Earth takes a shape _________. that conforms to the inverse-square law similar to that of an interior bar magnet of the field about a straight-length of current-carrying wire of an interior current-carrying coil

similar to that of an interior bar magnet

Because magnetic force on a moving electron is always perpendicular to its direction of motion, magnetic force cannot change an electron's direction. speed and direction. none of the above speed.

speed. A perpendicular force means no component of the force in the direction of motion to speed up or slow down an electron. The force can change direction, but not speed. This means that no work is done on the electron by a magnetic force.

When a current-carrying wire is bent into a loop, the magnetic field inside the loop cancels. none of the above weakens. strengthens.

strengthens. In all fields (electric, gravitational, and magnetic) the strength is proportional to the density of the field lines. When a length of current carrying wire is bent into a loop, the lines are concentrated, which strengthens the magnetic field inside the loop.

When an iron rod is placed inside a current-carrying coil of wire _________. the coil becomes an electromagnet only then does the coil have a north and south magnetic pole the coil becomes a stronger electromagnet more current is required to increase its magnetic strength

the coil becomes a stronger electromagnet

What happens when Dr. Hewitt places a current- carrying wire between the poles of the magnet for the first time? Nothing happens to the wire. The wire jumps up. The wire jumps down.

the wire jumps down

What happens when Dr. Hewitt turns the magnet around and places the current-carrying wire between the poles of the magnet for the second time? The wire jumps up. Nothing happens to the wire. The wire jumps down.

the wire jumps up

Does every magnet necessarily have a north and south pole?

yes

The magnetic force that acts on an electric charge at rest is _________. zero opposite in direction to the magnetic field in accord with the inverse-square law in a random direction

zero