Chapter Questions
Since every iron atom is a tiny magnet, why aren't all iron materials themselves magnets?
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 iron near the south pole of the magnet?
What is different about the magnetic poles of common refrigerator magnets compared with those of common bar magnets?
What surrounds a stationary electric charge? A moving electric charge?
"An electron always experiences a force in an electric field, but not always in a magnetic field." Defend this statement
Why will a magnet attract an ordinary nail or paper clip but not a wooden pencil?
A friend tells you that a refrigerator door, beneath its layer of white-painted plastic, is made of aluminum. How could you check to see if this is true (without any scraping)?
One way to make a compass is to stick a magnetized needle into a piece of cork and to float it in a glass bowl full of water. The needle will align itself with the horizontal component of Earth's magnetic field. Since the north pole of this compass is attracted northward, will the needle float toward the north side of the bowl? Defend your answer.
What is the net magnetic force on a compass needle? By what mechanism does a compass needle line up with a magnetic field?
Cans of food in your kitchen pantry are likely magnetized. Why?
We know a compass points northward because Earth is a giant magnet. Will the northward-pointing needle point northward when the compass is brought to the Southern Hemisphere?
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?
Magnet A has twice the magnetic field strength of magnet $\mathrm{B}$, and, at a certain distance, it pulls on magnet $\mathrm{B}$ with a force of $50 \mathrm{~N}$. With how much force, then, does magnet B pull on magnet A?
In Figure $17,$ 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?
A strong magnet attracts a paper clip to itselt 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 in the ship while in the shipyard are recorded on a brass plaque permanently fixed to the ship. Why?
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?
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. Which field performs which function?
A beam of high-energy protons emerges from a cyclotron. Do you suppose there is a magnetic field associated with these particles? Why or why not?
A magnetic field can deflect a beam of electrons, but it cannot do work on the electrons to change their speed. Why?
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?
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?
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 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?
Will a pair of parallel current-carrying wires exert forces on each other?
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?
Will a cyclist coast farther if the lamp connected to his generator is turned off? Explain.
If your metal car moves over a wide, closed loop of wire embedded in a road surface, will the magnetic field of Earth within the loop be altered? Will this produce a current pulse? Can you think of a practical application for this at a traffic intersection?
At the security area of an airport, you walk through a weak ac magnetic field inside a large coil of wire. What is the result of a small piece of metal on your person that slightly alters the magnetic field in the coil?
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?
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."
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 above if an iron core is inserted in the coils?
Why does a transformer require alternating voltage?
How does the current in the secondary of a transformer compare with the current in the primary when the secondary voltage is twice the primary voltage?
In what sense can a transformer be thought of as an electrical lever? What does it multiply? What does it not multiplv?
In the circuit shown, how many volts are impressed across, and how many amperes flow through, the lightbulb?
In the circuit shown, how many volts are impressed across, and how many amperes flow through, the meter?
How would you answer the previous question if the input were $12-V$ ac?
Can an efficient transformer step up energy? Defend your answer.
When a bar magnet is dropped through a vertical length of copper pipe, it falls noticeably more slowly than it does when it is dropped through a vertical length of plastic pipe. If the copper pipe is long enough, the dropped magnet will reach a terminal falling speed. Propose an explanation.
What is wrong with the following scheme? To generate electricity without fuel, arrange a motor to run a generator that will produce electricity that is stepped up with transformers so that the generator can run the motor and simultaneously furnish electricity for other uses.
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.