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

By whom, and in what setting, was the relationship between electricity and magnetism discovered?

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 currentcarrying 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 currentcarrying loop of wire greater than the field strength about a straight section of wire?

How is the strength of a magnetic field in a 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 Earths magnetic field have on the intensity of cosmic rays striking Earths 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 Faradays 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 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 about electric and magnetic fields?

Write a letter to a relative or friend saying that you have discovered the answer to what has been a mystery for centuries the nature of light. State 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 Earths magnetic field. The hammering jostles the domains so that they can better align with Earths field. The bar can be demagnetized by striking it when it is in an eastwest direction.

Earths magnetic field induces some degree of magnetism in most of the iron objects around you. 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 how many 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?

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.

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.

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

If the output current for the transformer in the preceding problem is 1.8 A, show that the input current is 0.36 A.

A transformer has an input of 6 V and an output of 36 V. If the input is changed to 12 V, show that the output would be 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. Show that: (a) 60 V ac is available at the secondary, (b) 6 A of current is in a 10- device connected to the secondary, and (c) 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 compared with the primary?

A power of 100 kW (105 W) is delivered to the other side of a city by a pair of power lines, between which the voltage is 12,000 V. (a) Use the formula P = IV to show that the current in the lines is 8.3 A. (b) If each of the two lines has a resistance of 10 , show that there is a 83-V change of voltage along each line. (Think carefully. This voltage change is along each line, not between the lines.) (c) Show that the power expended as heat in both lines together is 1.38 kW (distinct from power delivered to customers). (d) How do your calculations support the importance of stepping voltages up with transformers for long-distance transmission?

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 highest to lowest the readings on the galvanometer.

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

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

All atoms have moving electric charges. Why, then, arent all materials magnetic?

To make a compass, point an ordinary iron nail along the direction of Earths 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?

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

What is different about the magnetic poles of refrigerator magnets compared with those of bar magnets?

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

Will either pole of a magnet attract a paper clip? Explain what is happening inside the attracted paper clip. (Hint: Consider Figure 8.8 back in Chapter 8.)

Nails sticking to a magnet is understandable. Why are other nails attracted to the stuck nails, as in Figure 9.9?

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

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

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?

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?

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?

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

A strong magnet attracts a paper clip to itself with a certain force. Does the paper clip 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 answers.

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

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

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?

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

When walking in space, why do astronauts keep to altitudes beneath the Van Allen radiation belts?

What changes in cosmic-ray intensity at Earths surface would you expect during periods in which Earths 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?

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 travel 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?

Historically, replacing dirt roads with paved roads reduced rolling friction between vehicles and the surface of the road. 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 shown 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?

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.

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

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

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?

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.

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 lightbulb near, yet not touching, an electromagnet be lit? Is ac or dc required? Defend your answer.

Two separate but similar coils of wire are mounted close to each other, as shown. 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 being closed when the current is steady? When the switch is opened?

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

Why wont a transformer 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 thought of 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 each other, 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 the drop of a nonmagnetized object. Provide an explanation.

This exercise is similar to the preceding one. Why will a bar magnet fall slower 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 like a generator.

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

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.

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 Earths 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.

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. Do you suppose a magnetic field is associated with these particles? Discuss.

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.

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

Why doesnt a transformer work with direct current? Why is ac required?

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

A magician places an aluminum ring on a table, underneath which is hidden an 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.

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