Servicing projection equipment (1932)

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150 FORMULAS To Find Volts : Multiply figure expressing amperage by figure expressing ohms. (Amperage multiplied by ohms = voltage) Note: In applying electrical formulas to problems in projection, it must always be remembered that the arc voltage must be subtracted from the line voltage in order to arrive at a solution approximating conditions: for, although a voltage drop occurs in the wiring of the circuit, this can ordinarily be ignored; but arc voltage cannot, and thus voltage must be taken to mean line voltage minus arc voltage. Note: In order to get the exact arc voltage, have arc burning at its best normal adjustment, then touch a terminal wire of voltmeter to each carbon, making a good contact : the reading will be the figure you want to subtract from the line voltage in calculating. ARITHMETICAL FORMULAS Fractions To Add Fractions : First, both fractions must be reduced to a common denominator, that is, each must be expressed in terms of similar fractional parts, as, to add y2 and x/z. Both must be expressed similarly, which means, in this instance, as 6/12 and 4/12. Then the top figures can be added and the result will be 10/12, which can then be reduced to its lowest terms, which gives a result of 5/6. The procedure is to multiply both factors of each fraction by the denominator of the other. Thus: 2x3 1x4 4x3 and 3x4 To Multiply a Fraction by a Whole Number : Multiply the numerator | or r-by the whole number Divide the denominator J To Multiply a Fraction by a Fraction : Multiply the numerator of one by the numerator of the