A Few Words on Magnetism

Exercise 2. (Translate the text into native language)

Exercise 1. (Read the text)

Translate the following sentences.

Retell the main idea from the Text.

1. If an e.m.f. is applied to a path, the electrons will move toward the point of higher potential.

2. If people of the past had known that lightning was atmospheric electricity, they would not have invented numerous stories about it.

3. If a wire were held against an electrified body, electricity would flow along the wire to its other end.

4. If coal were not used as fuel, we should get more valuable products.

5. Were the electromotive force alternating, the current would be alternating as well.

6. Should you break the circuit, no current would flow.

7. Had they used a larger waiter pipe for their last experiment, more water would have passed through that pipe.

8. The current will flow around the circuit unless we break the circuit in some point.

***

Тема 14-15

Магнитный эффект электрического тока.

"Magnetic effect of electric current"

Kinds of magnets. Loadstone is classified as a natural magnet. It was discovered many centuries ago and one of the earliest practical uses made of the ore was in making compasses. Its use in the com­pass was known the world over by the time of Columbus.

Artificial magnets may be made by rubbing a piece of steel with a piece of loadstone. The steel may be in the form of a straight bar, or it may be bent much like a horseshoe with the ends or poles a short distance apart. Any magnet has a much stronger field when the ends or poles are close together, thus reducing the air gap.

Permanent magnets may be made by running an electric cur­rent through a coil of insulated wire wound around the piece of hard steel to be magnetized.

Poles. If a magnet is dipped into iron filings most of the filings will be attracted near the ends and only a few near the middle. Therefore, magnetism is stronger at the ends where it enters and leaves the magnet. These ends are called the poles of the magnet.

If the bar magnet is hung by a string so that it swings freely with no other metal or magnet near, it will come to rest with one end pointing North and the other end pointing South. Such action is due to the influence of the earth's magnetism which is always on the earth surface. Thus one end of a bar magnet is usually marked "N" and the other is marked "S".

In fact, these two poles are very different in action, the north pole of one magnet will attract the south pole of another but will repel the north pole. Let us suspend a bar magnet with marked poles, as in Fig. 1, by a string. Hold a second magnet as shown and observe the action. Notice, that the closer the magnets are together, the stronger the action.

Дата добавления: 2017-02-01