The Story Of Magnetism (1960)

[Music] [Applause] [Music] It has no fingers, but it can pick things up. It has no brain, but it can choose the things it picks up. You cannot sell a compass, a telephone system, a tape recorder. This is the story of magnetism and how we use it. Johnny uses magnetism. The operator of this electric crane uses magnetism. Men first learned about magnets thousands of years ago. They found that a certain kind of rock called magnetite attracted iron. They called pieces of magnetite load stone. A load stone suspended from a string comes to rest pointing north and south. It was found that an ordinary piece of iron when stroked by a load stone becomes a magnet. Later, mariners used magnets to make compasses. In the 16th century, Dr. William Gilbert, physician to Queen Elizabeth I, made a study of magnetism. He found that unlike poles attract and that like poles of magnets repel one another. He found that when a magnet is broken, each of the pieces acts like a magnet. Even if a magnet is broken into a thousand pieces, each piece will act like a magnet. Dr. Gilbert made an important discovery about the compass. People of his time believed that a compass pointed north because the north star was attracting the needle. Dr. Gilbert believed otherwise. He shaped a load stone into a sphere and moved a compass around it. He showed that the compass was affected by the load stone in much the same way as a ship's compass is affected when it moves about the earth. Dr. Gilbert concluded that the Earth itself acted like a huge magnet. He made tests to show that magnets would not attract such things as wood, glass, and many metals other than iron. He found that magnetism can pass through glass and other non-magnetic substances. Dr. Gilbert explained much about magnetism which he called a high and splendid power. Later men learned more about magnetism. When a bar magnet is held under a sheet of paper on which iron filings are placed, the filings form a pattern like this. These filings follow the invisible lines of force which make up a magnetic field. Every magnet is surrounded by a magnetic field. The lines of force are concentrated at the ends or poles of the magnet where the field is strongest. The earth too has a magnetic field. It has magnetic poles located near the north and south geographic poles. The magnetic field affects a compass. Pole of the compass needle points to the Earth's north magnetic pole. Compass needles, bar magnets, horseshoe magnets, and other common magnets are called permanent magnets. They tend to hold their magnetism. Many powerful permanent magnets are made from a combination of metals, iron, aluminum, nickel, cobalt, and copper. Permanent magnets are used in many ways. In the earpiece of telephones, in magnetic pot holders, can openers, screwdrivers, hammers, microphones, electrical measuring devices are used in many toys and games. Whatever its size or shape, whatever its use, every magnet is surrounded by a magnetic field. And the earth is surrounded by a magnetic field. A wire when an electric current is sent through it is also surrounded by a magnetic field. This was demonstrated in 1820 by Hans Erststead, a Danish teacher. He placed a wire over a compass. When he sent an electric current through the wire, the needle turned until it was at right angles to the wire. The current had created a magnetic field around the wire. When a wire is wound into a coil and an electric current is sent through it, a magnetic field is produced similar to the magnetic field around a bar magnet. A coil of wire is called a solenoid. When a current flows through it, the solenoid acts like a magnet. When a rod of soft iron is placed inside the solenoid, it becomes magnetized when the current is turned on. But when the current is cut off, the rod ceases to be a magnet. A piece of iron encircled by a coil of wire carrying a current is an electromagnet. This huge loading crane uses an electromagnet. a small electromagnet makes a doorbell ring makes possible the telephone, the telegraph, the loudspeaker of your radio or television set. These and many other things depend on magnetism produced by an electric current. Here is an experiment you can perform to show a relationship between a magnetic field and an electric current. Use a dry cell battery, a coil of wire, and a compass. Attach one end of the coil of wire to one terminal of the battery. Place the compass inside the coil. Now touch the other end of the coil to the other terminal of the battery. What does the movement of the compass needle show? How could you use this simple apparatus as an electric meter? We have seen that an electric current can produce magnetism. Now we will see that magnetism can produce an electric current. Over a hundred years ago, the English scientist Michael Faraday thrust a magnet into a coil of wire attached to an electric meter. The needle moved. An electric current was produced in the coil. You can test this yourself. Move a magnet into a coil of wire attached to a meter. How does the needle move? Quickly remove the magnet. Now, how does the needle move? What happens when the coil is moved instead of the magnet? When a coil cuts across magnetic lines of force, an electric current is generated. Faraday built the world's first magnetic generator of electricity. It consisted of a 12-in copper disc mounted so that it could be turned by a crank. As it turned, its outer edge passed between the poles of a large magnet. and electric current was produced. More efficient machines were soon built. Stronger electromagnets were substituted for the permanent magnet. A coil was used instead of Faraday's copper disc. Today's huge complex generators operate on the same principle. Scientists have learned much since the discovery that a load stone suspended from a string will point north and south. Dr. William Gilbert showed that the earth acts like a huge magnet. We know that magnets will attract some things like iron, steel, but not wood or glass. We know that every magnet is surrounded by a magnetic field. We can use iron filings to study the invisible lines of force which make up a magnetic field. We know that current flowing through a wire produces a magnetic field. Electricity can produce magnetism. We know that a solenoid can be made into an electromagnet to lift great weights. We know that magnetism can generate electricity. When a wire cuts across magnetic lines of force, an electric current is generated. There is still much we do not know about magnetism. Some scientists developed a theory which suggested that magnetic substances are made up of small particles which are themselves small magnets. This theory explained that when a material like this iron bar is not magnetized, the small magnets are scattered at random within the bar. What happens when the iron bar is magnetized? The particles line up with their north poles all pointing in the same direction. As scientists learn more and more about the nature of the atom, newer theories are developed. These new theories explain the nature of magnetism in terms of the motions of the electrons within the atom. It is the work of the scientist to continue to explore the nature of our world within the atom all about us and throughout the vastness of space. Heat. Heat. [Applause] [Music] [Applause] Heat. Heat.