Magnet Keeper

Magnet Keeper

Horse shoe Keeper

Magnet Keeper

 

1.9         Protection of magnetiom

Magnetism is lost if a magnet is heated red hot or dropped from a considerable height or beaten with a hammer. Magnets must be kept in a specific manner to ensure retention of magnetism for a long time. Let us now learn the technique of preserving magnets.

First keep two bar magnets with a wooden piece in between them so that their opposite poles point the same direction. Then join the opposite poles at each end with soft iron pieces. These are called magnetic keepers (fig 1.18). Similarly horseshoe magnet or U-shaped magnets are also preserved by using keepers (fig 1.19)

Earth's magnetiom : Why dies a freely suspended bar magnet or a magnetic needle come to rest in N-S direction ? What is the force that keeps them in the particular direction ? Earth itself acts as a permanent magnet. It has its magnetic north pole near its geographic south and its south pole near its geographic north (fig 1.20). Hence any freely suspended magnet or magnetic needle comes to rest in north-south direction.

Since Earth acts as a magnet, it has its own magnetic field. One of the effects of Earth's magnetic field is beautiful aurora formation.

A piece of steel that has been magnetized can lose much of its magnetism by improper handling. If it is jarred or heated, there will be a disalignment of its domains resulting in the loss of some of its effective magnetism. Had this piece of steel formed the horseshoe magnet of a meter, the meter would no longer be operable or would give inaccurate readings. Therefore, care must be exercised when handling instruments containing magnets. Severe jarring or subjecting the instrument to high temperatures will damage the device.

A magnet may also become weakened from loss of flux. Thus when storing magnets, one should always try to avoid excess leakage of magnetic flux. A horseshoe magnet should always be stored with a keeper, a soft iron bar used to join the magnetic poles. By using the keeper while the magnet is being stored, the magnetic flux will continuously circulate through the magnet and not leak off into space.

When bar magnets are stored, the same principle must be remembered. Therefore, bar magnets should always be stored in pairs with a north pole and a south pole placed together. This provides a complete path for the magnetic flux without any flux leakage.