. Motion picture electricity. ctive of the load. A constant potential transformeris the type required for electric power, incandescent lampsand constant potential arc lamps such as are usually em-ployed in factories, stores and theaters. MOTION PICTURE ELECTRICITY 51 It is not an easy matter to design and construct a trans-former which will regulate well, that is, hold the voltagesteady, whether one lamp or the entire number of lampsconnected are burning. If the transformer does not reg-ulate well, the voltage will be high when only a few lampsare burning and as more lamps or motors are switch
. Motion picture electricity. ctive of the load. A constant potential transformeris the type required for electric power, incandescent lampsand constant potential arc lamps such as are usually em-ployed in factories, stores and theaters. MOTION PICTURE ELECTRICITY 51 It is not an easy matter to design and construct a trans-former which will regulate well, that is, hold the voltagesteady, whether one lamp or the entire number of lampsconnected are burning. If the transformer does not reg-ulate well, the voltage will be high when only a few lampsare burning and as more lamps or motors are switchedon, the voltage will drop lower and lower. Modern trans-formers are constructed to give a practically constantvoltage irrespective of the load, and the regulating qual-ity of a constant potential transformer depends mainlyupon the amount of magnetic leakage. CONSTANT CURRENT TRANSFORMER If the magnetic leakage is great the transformer willnot regulate well and the voltage will drop more andmore as additional load is put Fig. 20 Fig. 20 illustrates a transformer having considerablemagnetic leakage because the primary and secondary coilsare some distance apart and are mounted on separate legsof the iron core. When the line current passes throughthe primary coil it generates magnetism in the iron coreand the current being alternating this magnetism is re-versed a given number of times per second, dependingupon the frequency of the current. If the secondary coilis not connected to any load, the magnetism will passthrough the iron as indicated by the arrows, first in onedirection, then when the current reverses in the other 52 MOTION PICTURE ELECTRICITY direction performing no work, simply keeping the ironcore excited, and the secondary coil under tension. If we should now put load on the secondary coil as indi-cated by the arc lamp in Fig. 21, all of the magnetism willno longer pass through the core leg upon which the sec-ondary coil is mounted, but some of the magnetic line
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