Motion picture projection : an elementary text book (1928)

Page scan 00052 from Motion picture projection : an elementary text book

Record Details:

Title:
Motion picture projection : an elementary text book
Date:
1928
Publisher:
New York : Technical Book Company
Volume:
Motion picture projection : an elementary text book
Leaf #:
00052
Language:
English
Subjects:
Motion Pictures, Motion Picture Technology
Collection:
Books
Format:
Books
Contributor:
Niles Essanay Silent Film Museum
Sponsor:
Media History Digital Library
Coordinator:
Media History Digital Library
Date Added:
May 08, 2025
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46 MOTION PICTURE PROJECTION The Watt. The electrical unit of power is the watt, and is equal to one joule per second ; that is, when one joule of work is expended in one second, the power is one watt. If the number of joules expended in a certain time is known, then the power in watts is obtained by dividing the number of joules by the time in seconds. The power is obtained by multiplying the current by the voltage, or by multiplying the square of the current by the resistance. The watt is sometimes called the volt-ampere. For large units the kilowatt is used, and this is equal to 1000 watts. The common abbreviation for kilowatt is K. W. The kilotvatt-honr is a unit of energy, and is the energy expended in one hour when the power is one kilowatt. Equivalent of Electrical Energy in Mechanical Units. The common unit of mechanical energy is the foot-pound, and from experiment it has been found that one joule is equivalent to .7373 footpound; that is, the same amount of heat will be developed by one joule as by .7373 foot-pound of work. As one horse-power is equal to 550 foot-pounds per second, it follows that this rate of working is equivalent to 550 = 746 joules per second (approx.). .7373 Hence one horse-power is equivalent to 746 watts. Therefore, to find the equivalent of mechanical power in electrical power, multiply the horse-power by 746 ; and to find the equivalent of