We all have played with magnets at some point in our childhood. Magnets have applications in many devices we use that we hardly notice them. A small introduction to magnets here.
What is a magnet?
A magnet is an object that can attract certain metals. It has an invisible field around it. This field is called the magnetic field. A magnet has two poles, called the North pole and the South pole. Magnets can be in any shape, the most visible shape most people have seen are horseshoe magnet and bar magnet.
Poles: Any magnet has exactly two poles, the north pole (N) and the south pole (S). They are named so as a freely suspended magnet always aligns itself in the north-south direction of the earth.
Magnetic field: It is a region in space surrounding a magnet where the magnet has an influence. If an iron piece comes within this field, it gets attracted.
Magnetic field lines: They are imaginary lines that emerge out of the north pole and enter the magnet through the south pole. Field lines exist within the magnet also.
- Place a magnet under a stiff cardboard.
- Sprinkle iron filings on the cardboard and tap the board.
- The iron filings align themselves along the magnetic field lines.
- We can see that the lines appear to come out or enter the poles, and directed from one pole to the other.
Properties of magnets
- Magnets attract certain metals like iron, nickel, cobalt. This is called attractive property. A magnet picking up steel pins, iron filings and nails, or sticking to a fridge door are because of this property.
- Similar or like poles repel each other. It means that the N-pole of one magnet pushes away the N-pole of another magnet. Similarly, the S-pole of a magnet pushes away the S-pole of another.
- Dissimilar or unlike poles attract each other. It means that the N-pole of one magnet attracts the S-pole of another magnet.
- A freely suspended magnet always aligns itself in the direction of the earth’s poles. This is called the directive property of a magnet.
- Magnetic poles always exist in pairs, called magnetic dipoles. No magnet can have only one pole. If a magnet is broken, each piece will have its own N-pole and S-pole. It is called pair property.
Natural magnets - Do they exist?
Definitely yes. If not, how else would humans would know that something that attracts iron would exist? In the Greek region of Magnesia, shepherds found that certain rocks would pull their iron tipped staff. They would find it difficult to walk on such rocks with their footwear that had iron nails. These rocks had natural magnetic property. People found that these amazing, magical stones not only attracted iron, but also aligned in the north-south direction when suspended with a thread. So they called these stones as lodestones, as they could easily find directions using these stones. Travelers and sailors started using these lodestones to find directions.
A natural magnet or lodestone is made of iron oxide, Fe3O4.
The earth as a magnet
We have seen above that a magnet aligns itself in the north-south direction when suspended freely. But why does it do so? The reason is, there is a huge magnet inside the earth. Its field covers the entire globe.
The N-pole of a magnet gets attracted by the south pole of the earth’s magnet that is located somewhere near the north geographical pole.
One of the theories suggested is that the molten iron core rotates around a solid iron core. This creates an electric current that sets up a magnetic field.
How is the earth's magnetic field useful?
- Since the magnet’s pole is near the geographical pole, it is easier to find the directions using a magnetic compass.
- Migratory birds are said to use the geomagnetic field to find their direction while journeying thousands of kilometers across oceans and vast stretches of land. The same holds good for migratory fish that travel thousands of kilometers in the ocean.
- One of the most important use is that life is possible only because of this field. The magnetic field diverts dangerous radiation that bombards out from the sun, and protects life on earth.
Read about artificial magnets in this article.
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