Sound motion pictures : from the laboratory to their presentation (1929)

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382 SOUND MOTION PICTURES Jack: A spring-contact receptacle into which a plug may be inserted for completion of one or more circuits. Key: A switch designed for easy and rapid manipulation. Kilocycle: One thousand cycles. Radio frequencies are conveniently expressed in kilocycles per second (abbreviated kc). A frequency of 500,000 cycles per second may be written 500 kc. Kilowatt (Abbr. K. W.) : One thousand watts, a unit used in measuring large amounts of electricity. Loudspeaker: A telephone receiver designed for relatively large powers and capable of producing sounds of sufficient volume to be heard through a room; usually fitted with a horn. Megohm: A unit of electrical resistance equal to one million ohms. Microampere: A unit of electric current equal to one one millionth of an ampere. Microfarad: A unit of electrical capacitance equal to one millionth of a farad. Microphone : (1) A loose electrical contact of variable resistance. (2) A telephone transmitter containing such loose contacts. (3) A device for converting sounds into electrical equivalents in a given circuit. In other words the microphone transfers sounds to a given electrical circuit by causing certain variations in the flow of electricity. It is the instrument used in both wire and radio telephony to transmit speech, and generally consists of a mass of loosely packed carbon blocks and subjected to varying pressure by the vibration of the diaphragm. (4) In a loose sense, the name is also applied to the transmitter used for picking up sounds in making sound pictures, although this instrument does not depend on microphonic contact action. Milliampere (Abbr. M. A.) : The thousandth part of one ampere.