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50 HANDBOOK OF PROJECTION FOR
Electrical Terms and Their Meaning
THERE are a few electrical terms with which the projectionist comes into quite intimate contact in his daily work. It is essential that he have a thorough understanding of what they actually represent to the end that he be able to use them intelligently in the various calculations arising from time to time in his work.
POLARITY. — Polarity and Potential mean the same thing. When wires are attached to opposite terminals of the same dynamo there is present in these wires an electrical condition which enables them to perform work. Properly cjnnect them to an electric motor and the energy in or on these wires will cause its armature to rotate and exert a pull and thus produce power.
Attached to a lamp the energy in or on these wires will cause the filament or the carbons thereof to become white hot, and thus produce light.
This electrical condition is termed "polarity" or "potential." It is, or it represents the electrical affinity which the positive wire of an electric circuit has for the negative wire of the same circuit, or the nega.ti.ve 'Wire of any circuit attached to the same dynamo. It represents the inclination of the electric impulse to "flow'' from positive to negative, which same is termed "current flow." See Page 3.
POSITIVE AND NEGATIVE AS APPLIES TO D. C.— When wires are charged with direct current one wire is continuously positive and the other negative
POSITIVE AND NEGATIVE AS APPLIES TO A. C.— When wires are charged with alternating current each wire of the circuit is alternately positive and negative many times every second. If it be 60 cycle current, then each wire is positive 60 times and each wire negative 60 times per second.
VOLTAGE OR ELECTRO MOTIVE FORCE (E. M. F.) .— Electric current is usually treated as having both pressure and volume. In its action as relates to these attributes, as well as regards the item of friction, electricity is very similar