Magnetism in Nature
What is Physics?
1) Physics is the science that deals with matter and energy and the relationships that exist between them. Physics is the most comprehensive of the natural sciences because it includes the behaviour of all kinds of matter – from the smallest particles to the largest galaxies. The word «physics» originates from a Greek word meaning natural things. Physics was originally called natural philosophy and included all natural science. As a large amount of knowledge was collected on a particular subject within natural philosophy, that subject branched off and developed into a separate science.
2) The various laws of physics are attempts by physicists to explain the behaviour of nature in a simple and general way. Even the most accepted laws of physics, however, are subject to change. Nature's behaviour does not change, but techniques for determining its behaviour do change and become more accurate. At the beginning of the 20th century, the laws of physics were tested extensively and were found to be too narrow to explain many of the new discoveries. A new body of theories was started. The older body of laws is called classical physics; the new is called modern physics.
3) Classical physics is based primarily on the laws of motion and gravitation of Sir Isaac Newton and the theory of electromagnetic radiation of James Clerk Maxwell. In classical physics matter and energy are two separate concepts. Matter is anything that occupies space and has mass. It exists in three basic forms. Plasma – highly ionized gas – has been called a fourth form. Energy is the capacity to move matter; as more commonly stated, it is the capacity to do work. Energy exists as mechanical energy, chemical energy, radiant energy, and nuclear energy. Some of the most important laws in classical physics are the conservation laws. Classical physics is usually divided into several branches, each of which deals with a group of related phenomena (mechanics, dynamics, hydromechanics, statics, optics, thermodynamics, acoustics, the study of electricity and magnetism).
4) Modern physics is based on the theory of relativity of Albert Einstein and the quantum theory of Max Planck and others. Matter and energy are not separate concepts, but are alternate forms of each other. The theory of relativity states that matter and energy are interchangeable and that mass and time can vary. Quantum theory states that light and other forms of electromagnetic radiation behave as though they have a double nature. Sometimes they behave as waves; at other times they behave as particles. Small particles of matter also have a double, or wave-particle, nature. Modern physics is broken up into various fields of study (atomic physics, nuclear physics, high-energy physics, or particle physics, ultrasonics, solid-state physics, plasma physics).
Magnetism in Nature
Most modern applications of magnetism use electromagnetism, which is created using electricity. However, there are several natural occurrences of magnetism.
Lodestone, or magnetite, was the first naturally occurring magnetic material to be discovered by man. Over 2,000 years ago, the Greeks, Romans, and Chinese all knew of lodestones and their magnetically attractive properties. Lodestones are composed of iron (chemical symbol Fe) and Oxygen (O) and have the composition Fe3O4. Lodestones are commonly found in nature, and have been found in large quantities in Scandinavia, South Africa, and the United States, as well as other places. Lodestones are among the strongest natural magnets, but they are relatively weak as compared to the synthetic magnets used in everyday life.
The strongest magnet on the Earth is actually the Earth itself! Although scientists are not absolutely certain of what causes the Earth’s magnetic field, they think it is caused by the liquid outer core of the Earth. This is mostly iron, and scientists believe it flows in currents; the motion of the molecules in these currents is theorized to create the Earth’s magnetic field. The Earth’s magnetic poles are not at the same places asthe geographic poles. The North Magnetic Pole is actually in far northern Canada, about 800 miles from the North Pole, and the South Magnetic Pole is off the coast of Antarctica, about 1,600 miles from the geographic South Pole. The magnetic poles tend to wander a bit, sometimes as much as 50 miles in a day. This is due to the interaction of the Earth and the solar wind. In addition to the daily variations, the Earth’s magnetic poles sometimes reverse themselves, with the North Magnetic Pole becomes south and vice versa. When this happens, the Earth’s magnetic field changes direction (and the sale of compasses increases dramatically). This happens about every 500,000 years.
Speaking of compasses, why do compasses point north? The needle of a compass is actually a small permanent magnet. The «north» tip of the compass needle is the north pole of its magnet, and is attracted to the North Magnetic Pole. The north pole of the magnet should not be attracted to the North Magnetic Pole if both are north poles. Similar poles should repel each other, yet the north pole of the compass magnet does indeed point «north». In reality, what we call the North Magnetic Pole is actually the South Pole of the Earth’s magnetic field! Similarly, the so-called South Magnetic Pole is actually the North Pole.
The Earth’s magnetosphere is a region above the Earth’s surface containing charged particles that are affected by the Earth’s magnetic field. It plays an important role in one of nature’s most picturesque magnetic phenomena, the auroras. Sunspots emit a large number of high-energy charged particles, some of which make their way through the Earth’s magnetosphere. These articles create an overload of charged particles in the lower Van Allen belt, which is basically a belt of radiation trapped around the earth. These excess charged particles enter the atmosphere near the Earth’s magnetic poles and collide with gas molecules in the atmosphere. These collisions make the molecules emit energy in the form of visible light. This happens for many molecules; their resulting light display is an aurora. In the northern hemisphere this display is called the Aurora Borealis, or northern lights. The equivalent southern lights are called the Aurora Australis.
Naturally occurring magnets are not used much these days.
(From Electricity and magnetism by John D. Carpinelli)
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