Man's physical universe

xanabras

UNIT VII

SECTION 3

AN ELECTRIC CURRENT USUALLY CONSISTS OF A

STREAM OF ELECTRONS

Introduction.

A stream of electrons is known as an electric current, the nature of

which forms the topic for this Section. It is true that an electric current

is produced when electrons stream from one charged body to

another through a conductor, but in so doing, the difference in potential,

due to the difference in charge, is equalized. Maintenance of an

electric current requires the renewal of the charge. Franklin could

entertain his friends with a dinner at which he served a turkey killed

by the discharge from a Leyden jar, but such a discharge will not

light city streets, run electric trains, nor cook the turkey.

Galvani Discovered Electric Currents.

Luigi Galvani (1737-1789), an Italian professor of anatomy and

obstetrics at the University of Bologna about 1768, noticed that the

severed leg of a frog contracted under the influence of a nearby electrostatic

machine. This observation aroused his curiosity, and he

determined to see whether or not atmospheric electricity would have

the same effect. Electricity, carried down a lightning rod specially

erected for this experiment, produced the same twitching when a

storm approached. He also found that this twitching was produced

when a nerve and a muscle were connected with two dissimilar metals

placed in contact with each other.

Galvani concluded from this experiment

that the source of the current was in the frog itself. How was

he to know that these two metals in contact with the saline juices in

the frog's leg constituted the world's first

observed chemical electric

cell? Galvani's work was of importance because it stimulated a great

deal of investigation. For this service alone it is quite fitting that he

be honored by having electric currents and instruments named after

him respectively as "galvanic" currents and the " galvanoscope " and

"galvanometer."

494

More magazines by this user
Similar magazines