Regions within the material called domains act like small bar magnets. What happens on a microscopic scale is illustrated in Figure 7(a). This causes an attractive force, which is why unmagnetized iron is attracted to a magnet. When a magnet is brought near a previously unmagnetized ferromagnetic material, it causes local magnetization of the material with unlike poles closest, as in the right side of Figure 20.7. Note that attractive forces are created between the central magnet and the outer magnets. The iron becomes a permanent magnet with the poles aligned as shown: Its south pole is adjacent to the north pole of the original magnet, and its north pole is adjacent to the south pole of the original magnet. A permanent magnet is simply a material that retains its magnetic behavior for a long time, even when exposed to demagnetizing influences.įigure 20.7 An unmagnetized piece of iron is placed between two magnets, heated, and then cooled, or simply tapped when cold. Not only do ferromagnetic materials respond strongly to magnets-the way iron is attracted to magnets-but they can also be magnetized themselves-that is, they can be induced to be magnetic or made into permanent magnets ( Figure 20.7). Other materials exhibit weak magnetic effects, which are detectable only with sensitive instruments. Such materials are called ferromagnetic, after the Latin word ferrum for iron. Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects. The north pole of a compass needle is attracted to the south magnetic pole of Earth, which is located near the geographic South Pole of Earth.The north pole of a compass needle is attracted to the north magnetic pole of Earth, which is located near the geographic South Pole of Earth.The north pole of a compass needle is attracted to the south magnetic pole of Earth, which is located near the geographic North Pole of Earth.The north pole of a compass needle is attracted to the north magnetic pole of Earth, which is located near the geographic North Pole of Earth.Toward which magnetic pole of Earth is the north pole of a compass needle attracted? Below, we will see that magnetic dipoles have properties that are analogous to electric dipoles. Because magnets always have two poles, they are referred to as magnetic dipoles- di means two. In fact, no experiment has ever found any object with a single magnetic pole, from the smallest subatomic particle such as electrons to the largest objects in the universe such as stars. As shown in Figure 20.6, you can continue this process down to the atomic scale, and you will find that even the smallest particles that behave as magnets have two opposite poles. You can even continue cutting each piece of the bar magnet in half, and you will always obtain a new, smaller magnet with two opposite poles. What happens if you cut a bar magnet in half? Do you obtain one magnet with two south poles and one magnet with two north poles? The answer is no: Each half of the bar magnet has a north pole and a south pole. Likewise, the south pole of magnets is attracted to the geographic South Pole of Earth. The magnetic south pole of Earth’s magnet is at the geographic North Pole, so the north pole of magnets is attracted to the North Pole, which is how the north pole of magnets got their name. For example, the poles of the bar magnet shown in Figure 20.2 are where the paper clips are concentrated.įigure 20.5 Earth can be thought of as containing a giant magnet running through its core. A magnetic pole is the part of a magnet that exerts the strongest force on other magnets or magnetic material, such as iron. These areas are called the poles of a magnet. When humans first discovered magnetic rocks, they likely found that certain parts of these rocks attracted bits of iron or other magnetic rocks more strongly than other parts. Magnetic rocks found in Magnesia, which is now part of western Turkey, stimulated interest during ancient times. The earliest records date back to ancient times, particularly in the region of Asia Minor called Magnesia-the name of this region is the source of words like magnet. People have been aware of magnets and magnetism for thousands of years.
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