Consequent poles One should never assume, without prior test, that a bar magnet always has opposite poles at its ends. If a steel bar is magnetized by divided touch using two S poles we obtain a N pole at both ends of the bar and a double S pole ill the center. In this condition the bar is […]
To magnetize a steel bar by the methods of single and divided touch Before the magnetic effect of an electric current was discovered in the early nineteenth century magnets were made by stroking steel bars with a lodestone or with another magnet. There are two ways in which this may be done, called the methods of single […]
To magnetize a steel bar by an electrical method The best method of making magnets is to use the magnetic effect of an electric current. A cylindrical coil wound with 500 or more turns of insulated copper wire is connected in series with a 6 or 12 V electric battery and switch (Fig. 30.4). A coil of […]
Test for polarity of a magnet The polarity of any magnet may be tested by bringing both its poles, in turn, near to the known poles of a suspended magnet. Repulsion will indicate similar polarity. If attraction occurs, no firm conclusion can be drawn, since attraction would be obtained between either: (a) two unlike poles or (b) a pole […]
Action of one magnet on another If the N pole of a magnet is brought near the N pole of a suspended magnet it is noticed that repulsion occurs. Similarly, repulsion is observed between two S poles. On the other hand, a N and a S pole always attract one another (Fig. 30.3). These results may be […]
Suspending a magnet. Magnetic axis. Magnetic meridian When a magnet is freely suspended so that it can swing in a horizontal plane it oscillates to and fro for a short time and then comes to rest in an approximate N-S direction. The magnet may be regarded as having a magnetic axis about which its magnetism is symmetrical, and […]
Magnetic and non-magnetic substances Apart from iron, the other common elements which are attracted strongly by a magnet are cobalt and nickel. These, together with certain strongly magnetic alloys are described as ferromagnetic. Substances such as copper, brass, wood, and glass are not attracted by a magnet, and are commonly described as non-magnetic. Nevertheless, experiments with very powerful […]
Magnetic poles If a piece of lodestone is dipped into iron filings it is noticed that the filings cling in tufts, usually at two places in particular (Fig. 30.1). When the experiment is performed with a bar magnet the filings are seen to cling in tufts near the ends. Few, if any, filings are attracted to the […]
Magnets As early as 600 B.C. the Greeks knew that a certain form of iron ore, now known as magnetite or lodestone, had the property of attracting small pieces of iron. Later, during the Middle Ages, crude navigational compasses were made by attaching pieces of lodestone to wooden splints floating on bowls of water. These splints always come to […]