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Transcript
From General to Specific
Worksheet
Task 2
Rearrange the following paragraphs so that resultant text follows a general –specific
pattern.
Faraday and Electro-Magnetism
(i) He was familiar with the phenomenon of electric induction. When an electrified body,
say a piece of amber, is brought near to an unelectrified body, the forces from the former
body separate out the two kinds of electricity in the latter, the further parts becoming
charged with electricity of the same sign as that on the amber, and the nearer parts with
electricity of the opposite sign; this is why rubbed amber attracts light pieces of paper, or
the needle of an electroscope. Faraday knew, too, that a magnet which is brought near to
an unmagnetised piece of iron induces magnetism in the latter, so that it and the magnet
attract one another; this is why a magnet picks up iron filings.
(ii) Faraday, pondering on these facts, wondered whether a current flowing in a circuit
might not in the same induce another current in a near-by circuit. He tried, without
success, to induce a current in a circuit by means of a magnet or a current in another
circuit. In 1831, he wound 203 feet of copper wire round a large block of wood,
interspersing another 203 feet of similar wire as a spiral between its turns, and preventing
electrical leakage between the two wires by binding both with twine. This gave him two
circuits in the closest proximity, with facilities for making a current in one and for
observing a current in the other. If the flow of a current in the first circuit induced a
current in the second, then the galvanometer1 included in the latter ought to show a
deflection. At first, none could be observed but Faraday noticed later a slight
instantaneous movement of the galvanometer in the second circuit, just at the moment of
starting the current in the first circuit. A similar movement occurred in the reverse
direction at the moment when the current was stopped.
(iii) In this way the mechanical work of moving a magnet could be made to produce an
electrical current. A way had been found to convert mechanical energy into the energy of
an electric current. On a larger scale the magnet might be moved by a cola-burning
engine, thus transforming the heat energy of coal into the energy of an electric current.
The science of electrical engineering had been born.
1
Galvanometer: instrument consisting of a coil of wire surrounding a smalll magnet and pointer. When an
electric current passes through the coil it produces a magnetic field at its centre and deflects the magnet.
(iv) For out of this fundamental experiment of Faraday has grown the whole vast
technology of the mechanical production of electric power, and of the structure and
operation of dynamos. The converse procedure of transforming the energy of an electric
current into mechanical energy lies at the basis of electric motors and of all forms of
electric transport – trains, trams, lifts and so on.
(v) Michael Faraday (1791 – 1867) was born in London, the son of a blacksmith and
began life as an errand boy for a book-binder. While he was thus employed, a customer
gave him tickets for some scientific lectures which Sir Humphry Davy was giving at the
Royal Institution. Here he attracted the interest of Sir Humphry, and finally was
appointed his lecture assistant.
(vi)The secret was now out. No current was induced in the second circuit by a steady
current in the first, but one was induced by changes in this current. Once this had been
established, it was only a step to see whether the current in the first circuit could be
replaced by a magnet, and Faraday soon found that the motion of a magnet in the
proximity of a circuit induced a current in the latter.
Adapted from The Growth of Physical Science. In English Studies Series 4 (1969).
Oxford: O.U.P
Answers:
(v) (i) (ii) (vi) (iii) (iv)