Magnetism - Electromagnetism and Electromagnetic Induction - science lessons for life


Monday, January 9, 2017

Magnetism - Electromagnetism and Electromagnetic Induction

Below Figure shows the use of a large electromagnet to lift and remove scrap iron and steel. Since iron and steel pieces are attracted towards this strong electromagnet, it is easy to move them using this method.
Use of an electromagnet to remove scrap iron and steel
There are two main types of magnets known as electromagnets and permanent magnets. In electromagnets, magnetism exists only while a current is passing through the coil of the electromagnet. In permanent magnets, magnetism is a characteristic of the material of the magnet and it remains in the magnet permanently.

Both types of magnets are used in many instruments for various purposes. Magnets are used in controlling most domestic appliances and robots by electric motors, in applications involving magnetic cards, in medical equipment such as MRI machines and in various other scientific and technological instruments. Therefore, it is useful to have a good knowledge about the behaviour, operation and applications of magnets.

Objects which are not attracted
attracted by magnets

Objects made of magnetic materials such as iron, steel, nickel are attracted by magnets. Objects made of materials such as plastic, wood, paper and rubber are not attracted by magnets.

Magnetic Field

Around any magnet, there is a region within which the magnet has an influence. This region is known as the magnetic field. A magnetic field is not perceptible to the eye. Therefore we cannot see a magnetic field. However, it can influence another magnet or a moving charge. It has been found that some animals such as birds use the earth’s magnetic field for navigation.

One way of determining whether there is a magnetic field in a certain region is to use a compass. A compass is a small light-weight magnet mounted on a pivot in such way that it could rotate freely around the pivot. In the absence of any magnetic influence other than the earth’s magnetic field, a compass aligns along the north-south direction. Let us engage in activity 13.1 to investigate the field near to a bar magnet.

Apparatus required: A compass, a piece of glass, A piece of iron, A magnet, A piece of plastic, a piece of brass

  • Place the compass on a table and observe the deflection of its indicator by bringing close to it, a piece of glass, a piece of iron, a magnet, a piece of plastic and a piece of brass one at a time.

You will observe that the indicator of the compass deflects only when a magnet is brought close to it. From this we can conclude that the magnet gives rise to a magnetic field in its vicinity.

When a compass is placed at a point in a region where a magnetic field exists, the direction of the compass needle shows the direction of the magnetic field at that point. This direction can vary from point to point. In addition, the strength of the magnetic field can also vary from point to point. Therefore, a magnetic field is a physical quantity with a magnitude and a direction.

Finding the direction of a magnetic field using a compass

source by internet and books

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