PHYS HW8

In what way are magnetic poles very different from electric charges? Magnetic poles only attract. Electric charges can attract or repel. The magnetic force between two poles is not the inverse square. Magnetic poles can exist as singular entities called magnetic monopoles. Electric charges are always paired as dipoles. All magnets have both south and north poles. Electric charges can exist as singular entities.

All magnets have both south and north poles. Electric charges can exist as singular entities.

When do cosmic rays penetrate your body? Mostly during the day When you're in deep caves All the time Mostly at night

All the time

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 Ants, bees, crickets, spiders, lions, and bears Bacteria, humans, bees, jellyfish, spiders, and sea horses Horses, sparrows, bees, jellyfish, cats, and anteaters

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

What is a magnetic domain? Clusters of atoms with their magnetic fields aligned 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

Solar winds headed in Earth's direction are deviated mainly by Earth's radiation belts. Earth's magnetic field. the troposphere. the upper atmosphere.

Earth's magnetic field

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

Electric charges in motion

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

Electric charges in motion are the sources of magnetic forces.

At the micro level, what is the difference between an unmagnetized iron nail and a magnetized iron nail? An unmagnetized nail is made of hard iron. A magnetized nail is made from soft iron. In an unmagnetized nail, the magnetic domains have a random orientation so that the net magnetism adds to zero. In a magnetized nail, many of the magnetic domains are aligned. An unmagnetized nail is made of iron at low temperatures. A magnetized nail is made from iron that is hot. An unmagnetized nail is made of an isotope of iron that is not magnetic. A magnetized nail is made from a magnetic isotope.

In an unmagnetized nail, the magnetic domains have a random orientation so that the net magnetism adds to zero. In a magnetized nail, many of the magnetic domains are aligned.

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

It reduces the intensity.

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

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

What is the cause of the aurora borealis (the northern lights)? As the Earth moves through the solar magnetic field, a voltage is built up between the south and north magnetic poles. This voltage accelerates charged particles to collide with both poles, thus causing the atmosphere to glow. Electrons in the Van Allen radiation belts flip over their spin direction and emit light. The northern lights are reflections of fluorescent lights from large cities off clouds in the arctic. 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.

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.

Why are there probably no permanently aligned magnetic domains in Earth's core? The core is too hot to allow atoms to maintain a constant magnetic orientation. The Earth's core is not made of magnetic iron or nickel. Meteorite impacts in the past vibrated the Earth's core and erased its magnetization. The Earth's core is completely liquid and magnetic domains cannot exist in liquids.

The core is too hot to allow atoms to maintain a constant magnetic orientation.

Why does a piece of iron in a current-carrying loop increase the magnetic field strength? The presence of the iron decreases the resistance in the current-carrying loop, thereby allowing more current to flow. The electromagnetic field of the current-carrying loop is amplified because it aligns the domains in the iron. The iron acts as a capacitor and stores spinning electrons, thus increasing the magnetic field. The iron is a permanent magnet and adds to the field of the current-carrying loop.

The electromagnetic field of the current-carrying loop is amplified because it aligns the domains in the iron.

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

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

In Chapter 22, we learned that the direction of the electric field about a point charge is radial to the charge. What is the direction of the magnetic field surrounding a current-carrying wire? The magnetic field is radial to the wire pointing away from the wire. The magnetic field is radial to the wire pointing toward the wire. The magnetic field is directed along concentric circles surrounding the wire. The magnetic field is parallel to the wire.

The magnetic field is directed along concentric circles surrounding the wire.

Why is iron magnetic and wood not? Iron atoms contain rotating electrons. The atoms in wood do not. Electrons in iron pair up with opposite spins. The atoms in wood are not paired. The magnetic fields of individual iron atoms are strong enough to align the magnetic fields of neighbor atoms. The atoms in wood have much weaker magnetic fields. Iron atoms have an even number of electrons, whereas the atoms in wood have odd numbers of electrons.

The magnetic fields of individual iron atoms are strong enough to align the magnetic fields of neighbor atoms. The atoms in wood have much weaker magnetic fields.

What are magnetic pole reversals? Bringing a stronger magnet near a weaker one causes the weaker one's poles to reverse. The magnetic field of the Sun is stronger than the magnetic field of Earth, so the reversal of the Sun's magnetic field forces the Earth's magnetic field to reverse, too. When new data is presented, scientists have to reverse their opinions on what is the origin of the Earth's magnetic field. The poles of the Earth's magnetic field undergo reversals.

The poles of the Earth's magnetic field undergo reversals.

Why will dropping an iron magnet on a concrete sidewalk make it a weaker magnet? Vibrations due to the collision recrystallize the iron, thereby cancelling the magnetism. General relativity applies in free fall and cancels the magnetic field. The collision with the sidewalk momentarily heats the iron to incandescent temperatures that erase the alignment of the magnetic fields of the domains. Vibrations provide energy to randomize the magnetic directions of the domains.

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

Surrounding every magnet is an electric field. a magnetic field. both of these neither of these

a magnetic field

Magnetic fields are produced by all moving electrical charges. most moving electrical charges. a tiny fraction of moving electrical charges.

all moving electrical charges.

An aurora borealis high above the atmosphere is due to disturbances in Earth's magnetic field. trapping of charged particles by Earth's magnetic field. fountains of high-speed charged particles. all of the above

all of the above

Cosmic rays penetrate your body when safely in your home. in mountainous regions. outdoors. all of the above none of the above

all of the above

To weaken a bar magnet put it in hot flames. drop it on a hard surface. whack it with a hammer. all of the above none of the above

all of the above

A current-carrying coil of wire is a superconducting magnet. an electromagnet. a magplane in the making. a superconductor.

an electromagnet

In general, a common magnet has one pole. at least two poles. only two poles.

at least two poles

Like kinds of magnetic poles repel while unlike kinds of magnetic poles repel also. may attract or repel. attract.

attract

A current-carrying wire in a magnetic field may experience a force. may be deflected. both of these neither of these

both of these

Surrounding every moving electron is a magnetic field. an electric field. both of these neither of these

both of these

The force that acts between a pair of electrically-charged particles depends on magnitude of charge. separation distance. both of these neither of these

both of these

The force that acts between a pair of magnetic poles depends on magnetic pole strength. separation distance. both of these neither of these

both of these

In the atoms of most materials the fields of individual electrons partly align. completely align. cancel one another.

cancel one another

Whereas electric charges can be isolated, magnetic poles can also. gather in clusters. cannot. none of the above

cannot

Magnetic field lines about a current-carrying wire circle the wire in closed loops. extend radially from the wire. both of these neither of these

circle the wire in closed loops.

The shape of a magnetic field surrounding a current-carrying conductor is circular. consistent with the inverse-square law. radial. all of these neither of these

circular

Magnetic field strength about a magnet is strongest where magnetic field lines are most curved. closer together. straightest. more spread.

closer together

An initially unmagnetized iron nail is placed near one of the poles of a magnet. An iron nail is more strongly attracted to the magnet if the nearest pole of the magnet to the nail is the south pole of the magnet. north pole of the magnet. either of these. The nail is not attracted to either of these.

either of these

Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is at or about 50 N. exactly 100 N. need more information

exactly 100 N

If you break a bar magnet in half you'll destroy its magnetic properties. have two and a half magnets. have two magnets. none of the above

have two magnets

Place an iron rod inside a current-carrying coil of wire and you have a superconducting magnet. increase the strength of the electromagnet. a magplane in the making.

increase the strength of the electromagnet.

Magnetic domains normally occur in copper. silver. iron. all of the above none of the above

iron

Wood does not have magnetic properties because it contains no moving electrons. iron or other metals. magnetic domains. none of the above

magnetic domains

The source of all magnetism is tiny pieces of iron. tiny domains of aligned atoms. ferromagnetic materials. moving electric charge. none of the above

moving electric charge.

The end of a compass needle that points to the south pole of a magnet is the north pole. south pole. both of these

north pole

The conventional direction of magnetic field lines outside a magnet are from north to south. either way south to north.

north to south

If a magnet produces a force on a current-carrying wire, the wire may or may not produce a force on the magnet. produces a force on the magnet. none of these

produces a force on the magnet.