Have you ever wondered why refrigerator magnets stick to the refrigerator door easily?
Magnets stick to the refrigerator door because, beneath the paint, the door is made of steel. A magnet is attracted to steel and hence sticks to the door.
A long time ago ancient people knew about the rocks that attracted metals. They were called lodestones.
The Greeks were the first to discover the phenomenon of magnetism about 4000 thousand years ago. A Greek shepherd named Magnes discovered a natural magnetic rock. This rock which had a compound of iron called magnetite was able to attract metals.
Ancient Chinese and Indians also knew about magnets.
In this chapter, you will learn about magnets, types and features of a magnet You will also learn about the properties and uses of magnets.
Magnetic Materials
Magnetic materials are those that are attracted by a magnet.
Examples: Steel, iron etc.
Non-Magnetic Materials
Non-magnetic materials are those that are not attracted by magnets. Do you know why the coins that we use are not attracted by a magnet? That s because, various metals are mixed together to make coins that are non-magnetic.
Examples: Paper, leather etc.
Magnetic Poles
Magnetic poles are the tips of a magnet and contain the highest magnetic strength. When a magnet is freely suspended, the tips point towards the north and south.
The tip pointing towards the geographical south is known as its south pole. The tip pointing towards the geographical north is known as the north pole.
Types of Magnets
Magnets are of the following two types, natural magnets and artificial magnets.
- A natural magnet is a naturally occurring substance with magnetic properties. Example: Magnetite.
- An artificial magnet is a substance into which magnetic properties are artificially induced.
- Examples: Magnets made of iron, cobalt, nickel etc.
- Artificial magnets can come in various shapes such as a dumb-bell shaped magnet, bar magnet, U-shaped magnet, cylindrical magnet, magnetic needle, etc.
- Artificial magnets are beneficial compared to natural magnets as they can be made in any desired shape.
- In addition to this, artificial magnets can be made very powerful that is not possible with natural magnets.
- Magnets made of an alloy that consists of aluminium, nickel, and cobalt (ALNICO) added to iron are the strongest magnets.
Magnets also classified as temporary or permanent based on their capacity to retain magnetism.
- Temporary magnets are those magnets which cannot retain their magnetism for a long time.
- Examples: Pure iron (Soft iron) and electromagnets that are made by passing an electric current through an iron piece.
- Permanent magnets are those magnets which retain their magnetism long after removal of the magnetising force.
- Example: Magnets made from steel (carbon + pureiron).
Uses of a magnet:
Magnets can be made into different size, shape and strength, based on their use. Devices such as TVs, loudspeakers, radios, telephones etc. make use of magnets.
Properties of Magnets
- A magnet attracts other magnetic material towards itself.
- Like poles repel each other. and unlike poles attract each other.
- A freely suspended bar magnet always aligns in the north-south direction.
- When a bar magnet is rubbed on an iron bar, the iron bar is converted into a magnet.
- There is no magnet with a single pole. Even when a magnet is cut into two pieces, each piece will behave as an independent magnet, with two poles, a north pole and a south pole.
Compass
Have you seen a compass? There must be one in the physics lab of your school. Most smartphones also have a compass. Ask your parent or neighbour to show you how the compass works.
As the needle in a traditional compass always points in the direction of the north, it is easy to find other directions easily. Let us see how the compass works.
- A compass is an instrument with a thin magnetic needle supported from a pivot.
- There is a round dial on the outer edge of the compass that marks the directions of North, South, East and West.
- The needle is positioned on a dial with marked directions.
- The north pole of the magnetic needle is painted with red colour.
- The magnetic needle in the compass always points towards the north-south direction.
- With the proper alignment of the dial, the directions can be found.
- An airtight box contains the entire assembly.
In the olden days, an old pointing device namely the south-pointing fish was used to find the directions. In this instrument, the fish head was pointed towards the south.
Storage of Magnets
A magnet gets demagnetised when left by itself for a long period of time. In other words, the magnet loses its magnetic property. This can be avoided by storing them between soft iron pieces also known as keepers when a magnet is not used. The Arrangement of bar magnets in pairs such that the opposite poles face each other and keeping two soft iron pieces at the two tips of the pair of magnets avoids demagnetisation of bar magnets.
How to Protect Magnets from Losing Their Magnetic Properties
Do not:
- Drop magnets from a height.
- Heat a magnet.
- Hammer a magnet.
Keep certain items such as DVD’s, debit cards, CD’s, audio and video cassettes, credit cards or ATM cards, and mobile phones which contain magnetic material, away from magnets to prevent damage.
Uses of Magnets
Magnets are used in:
- In stickers, magnetic toys, refrigerator doors, etc.
- Making magnetic compasses that help sailors and navigators to know directions.
- For separating iron from ores containing other non-magnetic substances.
- Removing tiny iron pieces that have accidentally fallen into the patient’s eye by eye doctors.
Electromagnets are used in:
- Generators, motors, loudspeakers, telephones, TV sets, fans, mixers, electric bells, etc.
- Cranes to lift heavy iron bars and to separate iron objects from scrap.
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