?We know that a compass points northward because Earth is a giant magnet. Does the

How does the range of refrigerator magnets differ from that of common bar magnets?

In what way is the rule for the interaction between magnetic poles similar to the rule for the interaction between electric charges?

In what way are magnetic poles very different from electric charges?

What produces a magnetic field?

What two kinds of motion are exhibited by electrons in an atom?

What is a magnetic domain?

Why is iron magnetic and wood not magnetic?

What is the shape of a magnetic field about a current carrying wire?

What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed?

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

How is the strength of the magnetic field in a current-carrying coil affected when a piece of iron is placed inside? Defend your answer.

In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? Minimum deflecting force?

What effect does Earth’s magnetic field have on the intensity of cosmic rays striking Earth’s surface?

What relative direction between a magnetic field and a current-carrying wire results in the greatest force on the wire? In the smallest force?

What happens to the direction of the magnetic force on a wire in a magnetic field when the current in the wire is reversed?

What is a galvanometer called when it is calibrated to read current? To read voltage?

Is it correct to say that an electric motor is a simple extension of the physics that underlies a galvanometer?

What important discovery did physicists Michael Faraday and Joseph Henry make?

State Faraday’s law.

What are the three ways in which voltage can be induced in a loop of wire?

How does the frequency of induced voltage compare with how frequently a magnet is plunged into and out of a coil of wire?

What are the basic differences and similarities between a generator and an electric motor?

Is the current that is produced by a common generator ac or dc?

What commonly supplies the energy input to a turbine

Is it correct to say that a generator produces energy? Defend your answer.

Is it correct to say that a transformer boosts electric energy? Defend your answer.

Which of these does a transformer change: voltage, current, energy, power?

What is induced by the rapid alternation of a magnetic field?

What is induced by the rapid alternation of an electric field?

What important connection did Maxwell discover between electric and magnetic fields?

Text a letter to a relative or friend and reveal that you have come to understand what has been a mystery for centuries— the nature of light. Explain how light is related to electricity and magnetism.

An iron bar can be magnetized easily by aligning it with the magnetic field lines of Earth and striking it lightly a few times with a hammer. This works best if the bar is tilted down to match the dip of Earth’s magnetic field. The hammering jostles the domains so that they can better align with Earth’s field. The bar can be demagnetized by striking it when it is in an east–west direction.

Earth’s magnetic field induces some degree of magnetism in most of the iron objects around us. With a compass, you can see that cans of food on your pantry shelf have north and south poles. When you pass the compass from their bottoms to their tops, you can easily identify their poles. Mark the poles, either N or S. Then turn the cans upside down and note the number of days it takes for the poles to reverse themselves. Explain to your friends why the poles reverse.

Drop a small bar magnet through a vertical plastic pipe, noting its speed of fall. Then do the same with a copper pipe. Whoa! Why the difference?

\(\text { Transformer relationship: } \frac{\text { Primary voltage }}{\text { Number of primary turns }}=\frac{\text { secondary voltage }}{\text { number of secondary turns }}\) The primary of a transformer connected to 120 V has 10 turns. The secondary has 100 turns. Show that the output voltage is 1200 V. This is a step-up transformer. Text Transcription: Transformer relationship: Primary voltage/Number of primary turns = secondary voltage/number of secondary turns

\(\text { Transformer relationship: } \frac{\text { Primary voltage }}{\text { Number of primary turns }}=\frac{\text { secondary voltage }}{\text { number of secondary turns }}\) The primary of a transformer connected to 120 V has 100 turns. The secondary has 10 turns. Show that the output voltage is 12 V. This is a step-down transformer. Text Transcription: Transformer relationship: Primary voltage/Number of primary turns = secondary voltage/number of secondary turns

A video game console requires 6 V to operate correctly. A transformer allows the device to be powered from a 120-V outlet. If the primary has 500 turns, show that the secondary should have 25 turns.

A model electric train requires 6 V to operate. When it is connected to a 120-V household circuit, a transformer is needed. If the primary coil of the transformer has 360 turns, show that the secondary coil should have 18 turns.

A transformer for a laptop computer converts a 120-V input to a 24-V output. Show that the primary coil has five times as many turns as the secondary coil.

Show that if the output current for the transformer in the previous problem is 1.8 A, the input current is 0.36 A.

A transformer has an input of 6 V and an output of 36 V. Show that if the input is changed to 12 V, the output is 72 V.

An ideal transformer has 50 turns in its primary and 250 turns in its secondary. 12-V ac is connected to the primary. (a) Show that 60 V ac is available at the secondary; (b) Show that 6 A of current is in a 10@ device connected to the secondary. (c) Show that the power supplied to the primary is 360 W.

Neon signs require about 12,000 V for their operation. Consider a neon-sign transformer that operates off 120-V lines. How many more turns should be on the secondary than on the primary?

A power of \(100 \mathrm{~kW}\left(10^{5} \mathrm{~W}\right)\) is delivered to the other side of a city by a pair of power lines, between which the voltage is 12,000 V. Text Transcription: 100 kW (10^5W)

Bar magnets are moved into the wire coils in identical quick fashion. Voltage induced in each coil causes a current, as indicated on the galvanometer. Neglect the electrical resistance in the loops in the coil, and rank, from greatest to least, the readings on the galvanometer.

Each of the transformers shown below is powered with 100 W, and all have 100 turns on the primary. The number of turns on each secondary varies as indicated. (a) Rank, from greatest to least, the voltage output of the secondaries. (b) Rank, from greatest to least, the current in the secondaries. (c) Rank, from greatest to least, the power output in the secondaries.

Many dry cereals are fortified with iron, which is added to the cereal in the form of small iron particles. How might these particles be separated from the cereal?

If you place a chunk of iron near the north pole of a magnet, attraction occurs. Why will attraction also occur if you place the same iron near the south pole of the magnet?

How do the magnetic poles of refrigerator magnets differ from those of bar magnets?

We know that a compass points northward because Earth is a giant magnet. Does the northward-pointing needle point northward when the compass is brought to the Southern Hemisphere?

What kind of force field surrounds a stationary electric charge? What additional field surrounds it when it moves?

What is the net magnetic force on a compass needle? By what mechanism does a compass needle align with a magnetic field?

All atoms have moving electric charges. Why, then, aren’t all materials magnetic?

Will either pole of a magnet attract a paper clip? Explain what is happening inside the attracted paper clip. (Hint: Consider Figure 8.8 in the previous chapter.)

A friend tells you that aluminum lies beneath the layer of white plastic on a refrigerator door. How could you check to see whether this is true (without any scraping)?

Magnet A has twice the magnetic field strength of magnet B, and at a certain distance it pulls on magnet B with a force of 50 N. With how much force does magnet B then pull on magnet A?

A strong magnet attracts a paper clip to itself with a certain force, does the paperclip exert a force on the strong magnet? If not, why not? If so, does it exert as much force on the magnet as the magnet exerts on it? Defend your answer.

To make a compass, point an ordinary iron nail along the direction of the earth’s magnetic field (which, in the Northern Hemisphere, is angled downward as well as northward) and repeatedly strike it for a few seconds with a hammer or a rock. Then suspend it at its center of gravity by a string. Why does the act of striking magnetize the nail?

Nails sticking to a magnet is understandable. But why are other nails attracted to the stuck nails, as shown in figure 9.9?

When steel naval ships are built, the location of the shipyard and the orientation of the ship while it is in the shipyard are recorded on a brass plaque permanently fixed to the ship. What does this have to do with magnetism?

How do force field lines for gravitation about a planet differ from force field lines for magnetism about electric currents?

Can an electron at rest in a magnetic field be set into motion by the magnetic field? What if the electron were at rest in an electric field?

When a current-carrying wire is placed in a strong magnetic field, no force acts on the wire. What is probably the orientation of the wire?

Two charged particles are projected into a magnetic field that is perpendicular to their velocities. If the charges are deflected in opposite directions, what does this tell you about the particles?

In Figure 9.17, we see a magnet exerting a force on a current-carrying wire. Does a current-carrying wire exert a force on a magnet? Why or why not?

Residents of northern Canada are bombarded by more intense cosmic radiation than are residents of Mexico. Why is this so?

When doing spacewalks, why do astronauts keep to altitudes beneath the Van Allen radiation belts?

What changes in cosmic-ray intensity at Earth’s surface would you expect during periods in which Earth’s magnetic field is passing through a zero phase while undergoing pole reversals?

When preparing to undergo a magnetic resonance imaging (MRI) scan, why are patients advised to remove metallic objects such as eyeglasses, watches, jewelry, and cell phones?

Historically, replacing dirt roads with paved roads reduced rolling friction between vehicles and the road surface. Replacing paved roads with steel rails reduced friction further. What will be the next step in reducing friction between vehicles and the surfaces over which they move? What friction will remain after surface friction has been eliminated?

A common pickup for an electric guitar consists of a coil of wire around a small permanent magnet, as described in Figure 9.26. Why will this type of pickup fail with nylon strings?

When Tim pushes the wire between the poles of the magnet, the galvanometer registers a pulse. When he lifts the wire, another pulse is registered. How do the pulses differ?

At the airport security area you walk through a metal detector, which consists of a weak ac magnetic field inside a large coil of wire. If your keys are in your pocket as you pass through the detector, or if you wear a pacemaker, why is an alarm sounded?

If your metal car moves over a wide, closed loop of wire embedded in a road surface, is Earth’s magnetic field within the loop altered? Does this produce a current pulse? Can you think of a practical application at a traffic intersection?

Two separate but similar coils of wire are mounted close to each other, as shown below. The first coil is connected to a battery and has a direct current flowing through it. The second coil is connected to a galvanometer. How does the galvanometer respond when the switch in the first circuit is closed? After it is closed when the current is steady? When the switch is opened?

Why will more voltage be induced with the apparatus shown above if an iron core is inserted in the coils?

Why is a generator armature harder to rotate when it is connected to a circuit and supplying electric current?

Does a cyclist coast farther if the headlamp connected to the bike generator is turned off? Explain.

How do the input and output parts of a generator and a motor compare?

Your friend says that if you crank the shaft of a dc motor manually, the motor becomes a dc generator. Do you agree or disagree? Defend your position.

Correct the statement that a generator produces energy.

Discuss what is wrong with the following scheme: To generate electricity without fuel, arrange a motor to run a generator that produces electricity that is then stepped up with transformers so that the generator can run the motor and simultaneously furnish electricity for other uses.

What is wrong with the statement that a very efficient generator can produce more power output than the power input that it consumes?

Why will a transformer not work in a dc circuit?

What is the principal difference between a step-up transformer and a step-down transformer?

In what sense can a transformer be viewed as an electrical lever? What does it multiply? What does it not multiply?

Can an efficient transformer step up energy? Defend your answer.

A friend says that changing electric and magnetic fields generate one another, and this gives rise to visible light when the frequency of change matches the frequencies of light. Do you agree? Explain.

Would electromagnetic waves exist if changing magnetic fields could produce electric fields but changing electric fields could not in turn produce magnetic fields? Explain.

Your physics instructor drops a magnet through a long vertical copper pipe, and it moves slowly compared with a non-magnetized object that is also dropped in such a way. Provide an explanation.

This exercise is similar to the previous one. Why will a bar magnet fall more slowly and reach terminal velocity in a vertical copper or aluminum tube but not in a cardboard tube?

Discuss why a motor also tends to act as a generator.

Both the English physicist Michael Faraday and the American physicist Joseph Henry independently discovered electromagnet induction at about the same time. In Henry’s electrical experiments, his wife sacrificed part of her wedding gown for silk to insulate the wires of his electromagnets. What was the purpose of the silk covering?

One method for making a compass is to stick a magnetized needle into a piece of cork and float it in a glass bowl full of water, as shown. The needle aligns itself with the horizontal component of Earth’s magnetic field. As the north pole of this compass is attracted northward, does the needle float toward the north side of the bowl? Defend your answer.

Your lab partner says, “An electron always experiences a force in an electric field, but not always in a magnetic field.” If you agree with him, defend his statement.

In a mass spectrometer, ions are directed into a magnetic field, where they curve around in the field and strike a detector. If a variety of singly ionized atoms traveled at the same speed through the magnetic field, would you expect them all to be deflected by the same amount? Or would you expect different ions to be bent by different amounts?

A cyclotron is a device for accelerating charged particles to high speeds as they follow an expanding spiral path. The charged particles are subjected to both an electric field and a magnetic field. One of these fields increases the speed of the charged particles, and the other field causes them to follow a curved path. Discuss which field performs which function.

A beam of high-energy protons emerges from a cyclotron. Discuss the magnetic field associated with these high-energy protons.

A magnetic field can deflect a beam of electrons, but it cannot do work on the electrons to change their speed. Discuss why this is so.

When Fred Cauthen releases the sheet of copper, why does it come to a halt as it begins its swing between the magnetic poles?

A piece of plastic tape coated with iron oxide is magnetized more in some parts than in others. When the tape is moved past a small coil of wire, what happens in the coil? What has been a practical application of this?

If you place a metal ring in a region where a magnetic field is rapidly alternating, the ring may become hot to your touch. Why?

How could a light bulb near an electromagnet, but not touching it, be lit? Is ac or dc required? Defend your answer.

Why can a hum usually be heard when a transformer is operating?

Why doesn’t a transformer work with direct current? Why is ac required?

A magician places an aluminum ring on a table, underneath which there is a hidden electromagnet. When the magician says, “abracadabra” (and pushes a switch that starts current flowing through the coil under the table), the ring jumps into the air. Explain his “trick.”

Do a pair of parallel current-carrying wires exert forces on each other?