Magnetism

Published by: BhumiRaj Timalsina

Published Date: 24 Jan 2022

Magnetism in Grade-7, Reference Note

The first magnet was found from the naturally occurring mineral called magnetite. The ancient Greeks were the discoverers of magnetite. There is a story about a shepherd named Magners whose shoe nails stuck to a rock containing magnetite while roaming on Mt. Ida. Later, it was found that the mountain was made of black stone with iron that had a special property to attract iron. It was an ore of iron called magnetite. Magnetite occurs all over the world, but there are especially large deposits in Scandinavia. The magnet was first used as a practical magnetic compass by the Vikings in their travels to colonise or in war. A magnet is a substance made of a certain material that has the capacity to attract magnetic substances like iron, nickel, cobalt, etc. The energy possessed by a magnet is called magnetic energy. We use the magnet in our daily life activities. It is used in loudspeaker, telephone, radio, telegraph, dynamos, toys, electric motors, etc. Magnet has always two poles, south pole, and the north pole. Like pole repels and unlike poles attract. The most powerful magnet in the universe is actually a star called a magnetar. Earth itself is like a one big bar magnet. Some animals are affected by magnets.
There are two types of magnets which are given below,

 

  1. Natural magnet:

    Those magnets which are found in nature is called natural magnet. They are found irregular in shape and it has the weaker force of attraction. Lodestone and magnetite are some examples of the natural magnet.
     
  2. Artificial magnet:

    Artificial magnets are those magnets that are made by humans by using various methods. They are of various shapes and sizes and has the strong force of attraction. Artificial magnets are generally made from special iron or steel alloys which are usually magnetised electrically. They may be bar-shaped, horseshoe-shaped magnetic needles, magnetic compass, etc. There are two types of artificial magnets which are as follows,

    Temporary magnet: Temporary magnets are the magnets that can retain their magnetic properties for the short period of time. They are made of soft magnetic materials like soft iron, steel, etc. They are magnetised by passing an electric current through an insulated wire, It creates the strong magnetic field due to which they are magnetised. They lose their magnetism when the electric current is stopped or external magnetic field disappears. An electromagnet is one of the examples of a temporary magnet. They are used in an electric bell, electric motor, electric fan, etc.

    Permanent magnet: These magnets retain their magnetic properties for the long period of time. They are made of hard magnetic substances like steel, cobalt, iron, etc. They are made of hard ferromagnetic material. They are used in speaker, transistor, radio, tape recorder, etc.

Methods of Making Magnets

There are various methods of making magnets. Magnets of desired shapes and sizes can be made artificially by using magnetic substances. Some common methods of making magnets are as follows,

Rubbing method


The artificial magnet can be prepared by rubbing strong bar magnet over the surface of magnetic substances for several times. It can be done by two methods,

Source: physicsmax.com Fig: Single touch method and double touch method

  1. Single touch method: In single touch method, a single magnet is rubbed over the surface of the magnetic substance in only one direction by using the same pole for several times. Magnetic substances like a blade, iron bar, iron clips, etc. can be magnetised.
  2. Double touch method: In double touch method, two magnets are used for rubbing. Here, unlike poles of two magnets are rubbed at the centre of magnetic substances for more than half an hour.

Electrical method:

Electrical method is used for making temporary magnets like an electromagnet. Here, the magnetic substances are magnetised by passing electricity. It consists of a coil made of insulated copper wire that is wound around the magnetic substance. The two ends of the wire are connected with the battery having a switch. When the switch is made on, the current flows through the coil and the magnetic substance becomes a magnet. When the switch is made off, the magnetic substance loses the magnetic properties. The magnets which are made by passing electricity are called electromagnet.

Source: 4mechtech.blogspot.com Fig: Electrical method

 

Precaution while making electromagnet

  • Instead of using naked wire, insulated copper wire should be used to prevent from short circuit.
  • The winding should be done only from one side.
  • The strength of the electromagnet can be increased by increasing number of turns of coil, amount of electric current and by using a soft magnetic substance.
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