The discovery of electro-magnetic induction

One day in 1819 a Danish physicist, Hans Christian Oersted, was lecturing at the University of Kiev, which was then a Danish town. Demonstrating a galvanic bat­tery, he held up a wire leading from it when it suddenly slipped out of his hand and fell on the table across a marine's compass that happened to be there. As he picked up the wire again he noticed to his astonishment that the needle of the compass no longer pointed north, but had swung completely out of position. He switched the current off, and the needle pointed north again. For a few months he thought over this incident, and eventually wrote a short report on it. No one could have been more surprised than Oersted at the extraordinary impact which his discovery made on physicists all over Europe and America. At last the longsought connection between electricity and magnetism had been found! Yet neither Oersted nor his colleagues could forsee the importance of this phenomenon, for it is the connection between electricity and magnetism on which the entire practical use of electricity in our time is founded.

Prompted by the research work of Andre-Marie Ampe­re, the great French physicist whose name has become a household word as the unit of the electric current, the Englishman Sturgeon experimented with ordinary, non-magnetized iron. He found that any piece of soft iron could be turned into a temporary magnet by putting it in the centre of a coil of insulated wire and making an elec­tric current flow through the coil. As soon and as long as the current was turned on the iron was magnetic, but it ceased to be a magnet when there was no more current. Sturgeon built the first large electro-magnet, and with this achievement there began the development of the elec­trical telegraph and later the telephone.

Every time he went for a walk in one of Lon­don's parks he carried a little coil and a piece of iron in his pocket, taking them out now and then  to look at them. It was on such a walk that he found the solution. Sud­denly, one day in 1830, in the midst of Green Park (so the story goes), he knew it: the way to produce electricity by magnetism was — by motion. He hurried to his laboratory and put his theory to the test.

A stationary magnet does not produce electricity. But when a magnet is pushed into a wire coil current begins to flow in the coil; when the magnet is pulled out again, the current flows in the opposite direction. This phenom­enon, confirms the basic fact that the electric current cannot be produced out of nothing — some work must be done to produce it. Electricity is only a form of energy; it is not a 'prime mover' in itself.

What Faraday had discovered was the technique of electro-magnetic induction, on which the whole edifice of electrical engineering rests.

Magnetic field

Fig. 2. Faraday's experiment

with the elec­tro-magnet

In America, Joseph Henry, professor of mathematics and natural science, also starting from Oersted's and Sturgeon's observations, used the action of the electric current upon a magnet to build the first primitive electric motor in 1829. At about the same time, Georg Simon Ohm, a German school-teacher found the important law of electric resistance: that the amount of current in a wire circuit decreases with the length of the wire, which acts as resistance. Ohm's excellent research work remained almost unnoticed during his life time, and he died before his name was accepted as tha of the unit of electrical resistance.

PHRASES & WORD COMBINATIONS TO THE TEXT

1. now and then – время от времени

EXERCISES

TASK 1. Answer the questions:

1. What was happened in 1819? _______________________________________

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2. What was it that Oersted discovered? _________________________________

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3. Did his discovery make any impression on physicists all over Europe and America? _______________________________________________________

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4. How did an electrically charged conductor work? ________________________

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5. Did he find that any piece of soft iron could be turned into a temporary magnet by putting it in the centre of a coil of insulated wire and making an elec­tric current flow through the coil? _______________________________________

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6. Who built the first large electro-magnet? ______________________________

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7. What did Faraday discover? _________________________________________

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8.Was Faraday’s experiment with the elec­tro-magnet succesful? ______________

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9. What is the important law of electric resistance? _________________________

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10.Who used the action of the electric current upon a magnet to build the first primitive electric motor in 1829? _____________________________________

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TASK 2. Translate the passage from “ What Faraday had discovered …” to ” … of the unit of electrical resistance ” in the written form.

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TASK 3. Fill in the blanks with words and word combinations from the text:

Prompted by the ___________ of Andre-Marie Ampe­re, the __________ whose name has become a household word as the unit of the ___________, the Englishman Sturgeon experimented with ordinary, non-magnetized iron. He found that any _______ iron could be turned into a __________by putting it in the centre of a coil of _________ and making an ___________ flow through the coil. As soon and as long as the current was turned on the __________, but it ceased to be a magnet when there was no more current.

TASK 4. Continue the sentenses according to the text:

1. One day in 1819 a Danish physicist___________________________________

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2. Demonstrating a galvanic bat­tery_____________________________________

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3. Nothing more than that_____________________________________________

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4. Prompted by the research work of Andre-Marie Ampe­re__________________

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5. Every time he went for a walk_______________________________________

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6. A stationary magnet does not________________________________________

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7. This phenom­enon, confirms the basic fact______________________________

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8. Thus Faraday demonstrated quite_____________________________________

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9. Meanwhile, fundamental research_____________________________________

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10. Georg Simon Ohm, a German school-teacher found the important law of electric resistance:_________________________________________________

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TASK 5. Translate into English:

Христиан Эрстед, читал лекции в Университете. Демонстрируя гальваническую батарею, он держал провод, идущий из нее, когда тот вдруг выскользнул из его руки и упал на стол прямо на морской компас, который случайно оказался там. Когда он поднялся провод, то он обратил внимание, к свому удивлению, что игла компаса больше не указывала север, а качнулась совершенно в другую сторону.

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