MAGNETISM

Magnetism is mentioned in the oldest writings of man. Romans, for example, knew that an object looking like a small dark stone had the property of attracting iron. However, nobody knew who discovered magnetism or where and when the discovery was made. Of course, people could not help repeating the stories that they had heard from their fathers who, in their turn, heard them from their own fathers and so on.

One story tells us of a man called Magnus whose iron staff was pulled to a stone and held there. He had great difficulty in pulling his staff away. Magnus carried the stone away with him in order to demonstrate its attracting ability among his friends. This unfamiliar substance was called Magnus after its discoverer, this name having come down to us as " Magnet".

According to another story, a great mountain by the sea possessed so much magnetism that all passing ships were destroyed because all their iron parts fell out. They were pulled out because of the magnetic force of that mountain.

The earliest practical application of magnetism was connected with the use of a simple compass consisting of one small magnet pointing north and south.

A great step forward in the scientific study of magnetism was made by Gilbert, the well-known English physicist (1540–1603). He carried out various important experiments on electricity and magnetism and wrote a book where he put together all that was known about magnetism. He proved that the earth itself was a great magnet.

At present, even a schoolboy is quite familiar with the fact that in magnetic materials, such as iron and steel, the molecules themselves are minute magnets, each of them having a north pole and a south pole.

The invention of the voltaic cell in 1800 gave electrical experimenters a source of a constant flow of current. Seven years later the Danish scientist and experimenter Oersted, decided to establish the relation between a flow of current and a magnetic needle. It took him at least 13 years more to find out that a compass needle is deflected when brought near a wire through which the electric current flows. At last, during a lecture he adjusted, by chance, the wire parallel to the needle. Then, both he and his class saw that when the current was turned on, the needle deflected almost at right angles towards the conductor. As soon as the direction of the current was reversed, the direction the needle pointed in was reversed too. Oersted also pointed out that provided the wire were adjusted below the needle, the deflection was reversed.

The above-mentioned phenomenon highly interested Ampere who repeated the experiment and added a number of valuable observations and statements. He began his research under the influence of Oersted's discovery and carried it on throughout the rest of his life.

V. Listen to the text “Electric Car” and mark the statements true, false or not stated

1. Women liked electric cars because they are smart and comfortable.

2. Electric cars were faster than gasoline-powered ones.

3. There were serious problems with the availability of oil in 1970s.

4. The General Motors Company had plans to develop an electric car by 1990.

5. Not many engineers believe that the electric car will lead to other forms of technology.

6. Electric car has no smell and makes no noises.

7. Nowadays car companies are working at developing a supercar.

8. To recharge an electric car’s batteries you have to plug the car into either a wall charger installed at your home or at a network of public charging sites around the country.

9. One of the possible power sources for supercar is solar energy.

10. A flywheel is an electric generator consisting of free-spinning wheels with magnets in the rims that can produce a current.

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