Magnetism is a property associated with materials that attract iron and iron alloys.
The science of magnetism probably began with early Greeks. From that time to the present many recognized the physical effects of magnetism, yet until this century, no one understood why certain materials were a magnet. Presently it is believed that all magnetic properties result from quantum mechanics and electromagnetic theory as applied to systems of many atoms.
A body that possesses the property of magnetism is called a magnet. Magnets can be termed natural or artificial. A natural magnet is a material or body that is magnetic in the state in which it is found; an artificial magnet is a body that possesses magnetism by induction.
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Some materials retain much of their magnetism long after an initial magnetizing force has been removed. These materials or bodies are called permanent magnets. Soft steel or iron retains only a small portion of the magnetism it receives by induction and can be considered a temporary magnet. Because soft steel alloys are so easy to magnetize and demagnetize they are used as cores for electromagnets. The core of the electromagnet becomes a strong magnet only when electric current flows in the coil of wire surrounding the core, as shown in the following figure. Causing more electric current to flow in the coil produces a stronger magnetic field.
In early experiments, it was noticed that a magnet, when freely suspended, orients its poles in a north-south direction. It was also found that pieces chipped from a magnet were magnetic and magnet ends attracted and sometimes repelled other magnet ends as shown in following figure in which we can observe repulsion between like poles and attraction between unlike poles. Note that in the compass, the markings of the poles are actually opposite to the nature of the magnet’s poles. For example, when the compass points toward North ‘N’, it is actually aligning with the south pole of the magnet inside the compass.
Fig.1: Unlike Poles Attract Each Other
Fig.2: Like Poles Repel Each Other
By experimentation, it was found that certain substances such as cobalt, chromium, and tungsten, when added in small amounts to steel, enhanced their magnetic properties. Similarly, heating a permanent magnet beyond a temperature (the ‘curie temperature’ for that material) will cause it to lose its magnetic property.