Man's physical universe

xanabras

UNIT VII

SECTION 4

THE DISCOVERY OF ELECTROMAGNETISM LINKED

MAGNETISM AND ELECTRICITY

Behind all your practical applications, there is a region of intellectual action

to which practical men have rarely contributed, but from which they draw all

their supplies. Cut them ofif from this region, and they become eventually

helpless. — John Tyndall.

Introduction.

Two discoveries of fundamental importance in putting electricity

to work were made in the nineteenth century. The first discovery,

made in 1820, that of H. C. Oersted, a Danish physicist, was that an

electric current produces a magnetic field in its vicinity. The second

discovery, in 1831, was made by Michael Faraday, who found that

under certain conditions a magnetic field

can be made to produce an

electric current. These two discoveries laid the foundations for the

harnessing of electrical energy.

In this Section the general characteristics

and applications of electromagnetism will be studied, reserving

Faraday's discovery and its applications for the next Section.

Oersted Discovered That an Electric Current Produces a Magnetic Field.

Once the chemical cell had been invented, thus furnishing a convenient

source of current electricity, investigators began to study the

possible relationship between electricity and magnetism. Oersted had

been trying to find out whether there was any effect when a wire

carrying a current was held above a compass at right angles to it.

No effect was noted. According to one story, he accidentally placed

the wire parallel to the needle during the course of a lecture and was

much surprised to see the needle turn aside. Oersted then tried placing

the wire below the needle, and the needle was deflected in the opposite

direction.

A. M. Ampere, a French investigator, after whom the unit of electric

current was named, worked out the principle of this relationship

between the electric current and the magnetic field and suggested that

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