Simple Phenomena of Magnetism

There are several elements that are magnetic, the most important of which are iron, cobalt and nickel. Scientists have developed alloys and ceramics made from complicated combinations of elements to get the exact properties that they want. Some of these materials are magnetically hard (such as steel, which is an alloy of iron, and other elements such as carbon or tungsten), This means that they stay magnetic once they have been magnetized. When we refer to a ‘magnet’, we mean a permanent magnet that is made of magnetically hard materials.

Other materials are magnetically soft (such as pure iron), which means that they do not stay magnetic – this is particularly useful in some electromagnetic devices such as the electromagnet and the relay.

Alloys are made by melting different metallic elements (iron, aluminium, copper, tungsten, etc.) together. The resulting metal is known as a ferrous metal if it contains a lot of iron, and as a non ferrous metal if it does not. Nickel and brass (copper + tin) are examples of non-ferrous metals.

In the past all magnetic materials were ferrous, but this is no longer true, and the strongest magnets may not contain any iron at all. for example, samarium-cobalt (SmCo, often used in headphones.

When we refer to ‘magnetically hard’ and ‘magnetically soft’ materials we are not referring to their physical hardness. You may have seen rubberized magnetic strips used on notice boards. These strips are permanent magnets, but are physically soft.

If a permanent magnet is suspended and allowed to swing, it will line up approximately north-south. Because of this, the two ends of a magnet (which are the most strongly magnetic parts) are called the north pole and the south pole, often labeled N and S. (Strictly, they are called the north- , seeking pole and the south-seeking pole.)

If two north poles from different magnets are brought together, there will be a repulsion between them. The same happens if two south poles are brought together. However, if a north pole and a south pole are brought together, there will be an attraction.

Magnets have a magnetic field around them – a region of space where their magnetism affects other objects. We describe the magnetic field using magnetic field lines. These lines show the path that the north pole of a magnet would take: heading away from a north pole and ending up at a south pole. The more concentrated the field lines are, the stronger the magnetic effect

Magnetic lines of force   North North pole lines

 

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Magnetic filed lines around a bar magnet

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