Magnetism—Powerful Servant of Man
MAGNETISM—what would life in this modern age be like without it? Why, it brings us the electricity that warms our homes, lights our roadways, cooks our foods, and does many chores for us daily! We could not enjoy fine music on a radio, watch a television program, or even pick up a telephone and call a friend, if it were not for magnetism.
Associated with this extraordinary force is something the Chinese called “The Stone That Licks Up Iron.” Sailors gave it the name lodestone, meaning “the stone that leads.” We call it a magnet, a name derived from the ore magnetite, which was plentiful in Magnesia, a district in Asia Minor. Regardless of the name, however, the mysterious power within the lodestone made it as precious as gold. Kings were fascinated by it. Sailors would navigate the oceans by means of a small sliver of it. Pagans thought that the gods sent the stone to guide them. But in spite of all the attention given to it, no one in the ancient world could have foreseen the tremendous potential of the force we call magnetism.
Today it is easy to obtain a magnet. Although the ore magnetite is not commonly available, man-made magnets of great power can be purchased for a small price. Many a child has amused itself for hours playing with a couple of small magnets. For that matter, magnets are so plentiful today that they often go unnoticed.
But just what is magnetism? How does it affect us? What is the source of its mysterious power? Let’s take a closer look at this powerful servant of man.
Characteristics of Magnetism
A few experiments with two bar-shaped magnets will help us to see some fundamentals of magnetism. Lay a piece of paper over the first magnet and sprinkle some iron filings (such as those from a nail) onto the paper. Tapping the paper a few times with your finger will cause these filings to form a strange pattern. Notice that all the small pieces of iron assemble themselves in lines that seem to loop out of one end of the magnet and into the other. Here we are observing just a small part of the magnetic field. These invisible lines of magnetic force actually surround the magnet completely, in all directions. The areas on each end of the magnet where all these lines converge are called the poles. Every magnet has two poles that cannot be separated from each other. If we were to cut our bar magnet in half, the result would not be two half-magnets, each possessing one pole. Rather, we would have two complete magnets, each having two poles, as did the original magnet.
Now that we have traced the magnetic field and identified the two poles of the magnet, let’s observe another very interesting property of magnetism. Tie a string around the middle of the magnet and suspend it in the air. You will notice that one end of the magnet will swing around until it points to the north. Move it away and it will always swing back to the north. The pole of the magnet that points to the north is called the north-seeking pole, and the one that points to the south, the south-seeking pole. This property of magnetism is the basis for the compass. But what causes this phenomenon?
To find out, we will need to use the second magnet. On each magnet let’s mark the pole pointing north with an N, and the one pointing south with an S. Now take one magnet in each hand and move the N of one magnet near the S of the other. What happens? There seems to be an invisible force that pulls them together. But reverse the position of one of the magnets, putting the N’s or the S’s together, and the force now seems to push them apart. This demonstrates an unchangeable law of magnetism, namely, opposite poles always attract, whereas like poles always repel.
This is why one end of a magnet always swings to the north. The earth itself has a magnetic field, just as the bar magnet does. This field extends far out into space and converges at each of the earth’s poles. So, a magnet’s north-seeking pole will always be attracted by the North Pole of “magnet earth,” while being repelled by the South Pole.
Probably the most familiar characteristic of magnetism is its ability to attract metals. Not all metals are drawn to a magnet, however. Brass, aluminum, gold and silver are not attracted to a magnet, whereas iron, steel, nickel, cobalt, chromium and other metals are attracted, though in varying degrees. Interestingly, the attractive power of a magnet is the same at both of its poles. Hence, an iron nail, for example, will be attracted just as strongly by either end of our bar magnet.
Our look at these basic characteristics of magnetism leaves us with very important questions yet to be answered. What is the source of this power? Yes, just what causes magnetism? And why are not all metals magnetic?
Finding the Cause of Magnetism
To answer the foregoing questions, we will have to examine the basic building block of matter, the atom. It consists of a tightly packed nucleus made up of protons and neutrons, with varying numbers of electrons circling around it, much as the planets of our solar system orbit the sun. This movement of electrons actually results in a minute magnetic force within the atom. Most electrons are paired in such a way that their magnetic fields cancel each other. When all the electrons in an atom are paired, the net magnetic field is zero. Metals composed of such kind of atoms are nonmagnetic.
But if the atom has unpaired electrons, it has a net magnetic moment, as the scientists call it. The strength of this magnetic moment determines how the atoms line up in the solid metal. In most metals, the agitation of the atoms at ordinary temperatures is great enough to overcome the magnetic forces, and the atomic magnets are disarranged, in random directions. The net resultant of the magnetic fields of a large number of atoms averages out to zero.
However, magnetism can be induced in such metals when they are placed in another magnetic field. Chromium is such a metal. The force of the magnetic field causes the atoms to turn into a parallel alignment. But as soon as it is removed from the field, thermal agitation again prevails, and this destroys the alignment. The chromium loses its magnetism. Metals like this, which do not retain magnetism, are called paramagnetic.
By contrast, in some metals, including iron, cobalt, and nickel, the individual atoms have much stronger magnetic moments. They are so strong that when atoms are crystallizing out of a melt, one atom feels the influence of its neighbor, and clusters of atoms align themselves with their magnetic axes parallel. Each such group actually becomes a small magnet. However, these clusters are microscopic in size and they are randomly oriented in a fresh casting. Thus an ordinary iron nail, for example, is not a magnet.
But if a piece of iron is placed in a magnetic field, the groups that happen to be in line with the field tend to grow at the expense of neighboring groups, by pulling adjacent atoms into line with them. This action is enhanced if the metal is heated, or stressed as by drawing. The alignment formed in this way persists when the iron is removed from the field. Thus the metal has become a permanent magnet. Such metals, which can be permanently magnetized, are called ferromagnetic. The iron atoms in magnetite were so aligned, apparently by the earth’s magnetic field when the ore was crystallizing.
The larger the groups are that are aligned with the field, and the smaller the ones that are randomly oriented, the more powerful will be the resultant permanent magnet. Scientists have learned that by applying heat or stress on the metal while it is within a powerful magnetic field, the maximum number of atomic groupings can be permanently aligned. In this way, permanent magnets of great strength can be produced economically.
As mentioned earlier, the earth itself is one large magnet. What causes this globe’s magnetic field? Some have thought that it was caused by the naturally magnetic ores within the earth. In other words, they have considered the earth to be a giant permanent magnet. But in more recent times it has been learned that the very high interior temperature of the earth rules out that possibility.
Today the most commonly accepted explanation is that our globe’s magnetic field results from electric currents in the earth’s core, in some way related to the revolution of the earth on its axis. There is evidence also that other planets are magnetic. Jupiter, in particular, has a field much stronger than the earth’s. And the sun itself has an extremely powerful magnetic field. Even the Milky Way, the galaxy that includes our sun and some hundred billion other stars, gives evidence of having a magnetic field.
The role of the earth’s magnetic field in protecting life is just being brought to light by scientists. An example of this can be seen in connection with the violent magnetic storms on the surface of our sun (known as “sunspots”). The gigantic regions of concentrated magnetic fields in the hot solar atmosphere actually cover areas larger than the earth, and have magnetic fields that are over a thousand times stronger than that of our globe. The sun continually sprays into space streams of electrically charged particles, which are called the “solar wind.” This wind would be devastating to earthly life, but our magnetic field traps the solar particles out in space before they even reach the atmosphere. It bends their paths into spirals around the lines of magnetic force and funnels them into the atmosphere in the north and south polar regions. Even so, when there is a severe magnetic storm on the sun, we can expect shortly afterward a geomagnetic storm that disrupts radio transmission, radar, and even power distribution. It also produces the grand ‘fireworks displays’ that are called the aurora borealis and aurora australis, the “northern lights” and “southern lights.”
The earth’s magnetic field also helps to protect us from the most damaging cosmic rays by diverting them to the polar latitudes. We probably do not yet fully realize in how many ways this magnetic “cushion” serves to our benefit. But it is becoming evident that the magnetism of our planet plays a key role in protecting life.
Electricity and Magnetism
Magnetism’s ability to serve mankind especially lies in its relationship to electricity. Remember that the minute electrical current within the atom causes magnetism in the first place. In fact, magnetism and electricity are so closely related that each one causes the other. How is this so?
Electricity flowing through a wire causes that wire to become magnetized. No, the wire will not attract other metals because the magnetic field surrounds the wire in a circular pattern, having no definite poles. But if the wire is coiled like thread on a spool, the magnetic field around each coil amplifies that of its neighbor, resulting in one large magnetic field. The more numerous the loops or coils of wire, the stronger the magnet produced. This magnet can be turned on and off simply by turning on and off the electricity flowing through it. If there is no electrical current, there is no magnetic field. This type of magnet is called an electromagnet.
A simple example of an electromagnet in action is the common doorbell. When you push the button, electricity flows through an electromagnet, attracting a hinged piece of metal to it. In its movement toward the electromagnet, the metal strikes a chime. When you release the button, the electromagnet releases the metal, and as it springs back to its original position, it strikes another chime, resulting in the familiar “ding-dong.” In this, and sometimes in more complex ways, magnets and electromagnets are at the heart of most electrical appliances.
Electric motors are based on the electromagnet. To state it simply, electromagnets arranged in a circle are turned on and off at precisely timed intervals, and the attractive/repulsive properties of the magnets set an armature spinning within the circle. Thus electric motors of varying strengths do many chores for us, from turning the hands on our clocks to speeding heavy commuter trains to their destinations.
Switches, relays, solenoids, meters, gauges, and so many other instruments of the electrical industry are based on this simple relationship between electricity and magnetism. Why, magnetism permits the sound of your voice to be transmitted over telephone wires to your loved ones, and then allows you to hear their voices in reply! Electromagnets within the speakers of your radio, television or stereo set convert electrical impulses into sound, reproducing the original with amazing fidelity. Yes, magnetism allows you to make a tape recording of your son’s first words, or your daughter’s first violin solo, and to relive those precious moments years later.
It is a beam of electrons focused precisely by magnetic fields that produces the picture on your television set. This same focusing of electron beams by magnetism allows scientists to peer into the world of the infinitesimally small by means of electron microscopes.
Electricity’s relationship to magnetism works in a converse way as well. The generators that produce electricity depend on magnetism. Powerful permanent magnets are arranged in a circle, and turbines driven by steam or water cause coils of wire to rotate through these powerful magnetic fields. This movement of the wire causes an electrical current to flow in the wire. Then this current is transformed to a suitable voltage and passed on to our homes.
It would not be an overstatement to say that the entire electrical industry would not exist today if it were not for that powerful servant of man that we call magnetism.
There are many things yet to be learned about magnetism, and the more scientists learn about this power, the more uses they find for it. For example, a new technology called magnetohydrodynamics (MHD) promises to make the generating of electricity even more economical than it is today. Most major cities now use steam turbines to run their generators, and fossil fuels such as coal are burned to produce the steam. By means of MHD, though, it would be possible to produce electricity, not only in the generator, but also in the smokestack. How? Well, when the hot gases resulting from burning coal are channeled through a magnetic field, an electric current is produced. This revolutionary new system can convert the energy from coal into electricity, doing so with greater efficiency than any other system makes possible. Some researchers say that the increase in electricity produced from a ton of coal by means of MHD is as much as 50 percent. MHD also has been proposed as a method of extracting power from certain types of atomic reactors.
In the field of transportation, progress is being made in developing trains that “fly” above special tracks by means of “magnetic levitation.” Electromagnets placed on the train and in the track bed cause the train to float about a foot above the guideways, and then to be propelled forward at remarkable speeds. Tests in Germany and Japan indicate that such trains will move passengers at speeds of up to 190 miles (306 kilometers) per hour. High-speed transportation systems based on magnetic levitation have both economic and environmental advantages over other systems. For example, there are no moving parts to wear out, smaller amounts of energy are consumed, and they are nonpolluting and silent in operation.
Man is just beginning to ‘scratch the surface’ in his quest for more uses of magnetism. Increased knowledge of such dynamic power within our universe may well cause us to reflect on the might of Jehovah God, the Creator of such forces. He is ‘abundant in dynamic energy and vigorous in power,’ and has originated magnetism—that powerful servant of man!—Ps. 147:5; Isa. 40:26.
[Pictures on page 19]
In nonmagnetized metals, small atomic groups are arranged with their magnetic poles situated at random
When magnetized, atomic groups realign themselves so that they lie parallel to one another
[Pictures on page 20]
The magnetic field around a wire with electricity flowing in it is shaped like a doughnut and has no definite poles
When the wire is coiled, electrical current within it will produce an electromagnet with definite magnetic poles
[Picture on page 21]
High-speed trains that “fly” above special tracks by means of “magnetic levitation” are being developed