Page 333 - NS-2 Textbook

328 NAUTICAL SCIENCES

ELECTRON FLOW
JUNCTIOmNil~~,.

COPPER OXIDE

PURE COPPER BASE
Voltage produced by light.

Voltage produced by heat.

the surface atoms. Voltage produced in this man-
ner is called plioloelectric. The plioloelectric cell is
the device that operates on this principle. A plate
coated with compounds of silver or copper
oxide, which are extremely sensitive to light, can
also produce a flow of electrons. Light is used to
generate voltage in devices requiring extreme
precision-such as television cameras, automatic
processing controls, door openers, and burglar
alarms.
5. Cliemical action. Voltage can be produced by ZINC-..... o:l.
chemical reactions, as in a battery cell. The sim- (Zn)
ple voltaic battery consists of a carbon strip (pos-
itive) and a zinc strip (negative) suspended in a
container with a solution of water and sulfuric Simple one-cell battery.
acid. This solution is called the electrolyle. The
chemical action that results from this combina-
tion causes electrons to flow between the zinc
and carbon electrodes. Batteries are used as
sources of electrical energy in automobiles,
boats, aircraft, ships, and portable equipment.
6. Magnetism. Voltage can be produced when a con-
ductor moves through a magnetic field, or vice
versa, in such a manner as to cut the field's lines
of force. This is the most common source of elec-
tric power; it is the method used in electric gen-
erators. Usually, a copper-wire conductor is
moved back and forth through the magnetic OF MOTION
field created by a U- or C-shaped electromagnet.
Voltage produced by magnetism.
An instrument designed to measure voltage in an
electrical circuit is called a voltmeler.
pere (or amp) is the uuit used to measure the rate at which
current flows. The symbol for current flovv is NI."
CURRENT
An instrunlent designed to measure current in an
The flow of electricity through a conductor is called elec- electrical circuit is called an ammele/:
tric cllnenl. Electric current is classified into two general Every Inaterial offers some resistance or opposition
types: direct current and alternating current. Direct Cllr- to the flow of electric current. Good conductors offer
rent flows continuously in the same direction, while an very little resistance, while insulators or poor conductors
alternating clIrrent periodically reverses direction. An am- offer high resistance. The size and composition of wires