Magnetisation and demagnetisation

Most magnets are made of iron or steel because iron is a fairly cheap metal. 
In a magnetised piece of iron, there are magnetised domains. Electrons of atoms are grouped into domains in which each domain has the same charge. These domains are lined up and point the same way. This is what makes a magnet a magnet.  

Why are magnets magnetic?

You can magnetise a piece of iron or steel easily.

Activity 1

What you will need:

A piece of steel or a long steel or iron nail

A bar magnet

drawing pins, iron nails or paper clips

insulated copper wire

4.5 V battery

What you will do:

Part 1

1. Check that the nail or piece of steel is not magnetised by dipping it into a dish of the drawing pins.

2. Stroke the piece of steel with the N-pole of the magnet. Start at the marked end and lift the magnet clear at the end of each stroke. Do this about 10 times in the same direction. 

How many pins can the steel pick up now? 

Place the N-pole of the bar magnet near to the magnetised piece of steel. Does it attract or repel? 

The mark on the piece of steel you magnetised will be the north pole of your magnet. 

Part 2:

1. Wind about 1 meter of insulated copper wire around a large iron nail. Connect the ends of the wire to the battery as shown in the picture below:

Image: Flickr. Clifford, G. (CC BY-SA)

2.  Try and pick up the pins. How many can you pick up?

This is called an electromagnet. Coiling copper around a nail and connecting it to a source of electrical energy creates a non-permanent magnet. These types of magnets are used in cranes, telephones, and fridge doors. 

Image: StackExchange (CC BY-SA)

Demagnetisation

Demagnetisation is the process by which a magnet loss its magnetism. The domains get misaligned (disoriented).

A magnet can undergo self-demagnetisation if poorly stored or the process can be influenced externally by giving the dipoles enough energy to overcome the forces holding them in a particular direction.

Demagnetisation can be hastened by any of the following methods:

• Hammering.  Hammering a magnet repeatedly while placed in the east-west direction or dropping it violently several times on the hard surface makes it lose most of the magnetism.
• Heating.  Heating a magnet until red hot and cooling it suddenly when resting in the east-west direction makes it lose its magnetism.
• Electrical method.  Placing a magnet in a solenoid placed in east-west direction and passing an alternating current demagnetises it. This is because alternating current reverses many times per second, disorienting the magnetic dipoles.