. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. oduct of thepressure multiplied by the current at that instant, a curve maybe easily plotted from the pressure and current curves, giving theinstantaneous values of the power through a complete cycle. In fig 1,344, from the zero line of the current and pressure curves,draw any ordinate as at F cutting the current curve at G and the pressure 1,104 HAWKINS EL
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. oduct of thepressure multiplied by the current at that instant, a curve maybe easily plotted from the pressure and current curves, giving theinstantaneous values of the power through a complete cycle. In fig 1,344, from the zero line of the current and pressure curves,draw any ordinate as at F cutting the current curve at G and the pressure 1,104 HAWKINS ELECTRICITY curve at G. The value? for current and pressure at this point are fromthe scale, 2 amperes and volts. Since watts = amperes X volts, theordinate FG is to be multiplied by ordinate FG that is, 2 X = Project up through F the ordinate FG = , and this will give onepoint on the power curve. Similarly at another pcint, say M, where the current and pressureare maximum MS X MS = MS, that is3 X 5 = 15 giving S another point on the curve. Obtaining several points in thisway the power curve is then drawn through them as shown. 1 ca _ * _ sra z — ? - — < | - = c **E r - .-- - < ■ ~ *5 1 . — = M £ — = :. PlC —Irjil method of drawing power curve from the pressure and current smaller scale is employed for the power curve in order to reduce its height. Ques. Why is the power curve positive in the secondhalf of the period when there are negative values of cur-rent and pressure? Ans. Because the product of two negative quantities ispositive. Ques. Does fig. 1,344 represent the usual way of draw-ing a power curve? Ans. Since ordinates of the power curve are products of thecurrent and pressure ordinates, they will be of inconvenient THE rOWER FACTOR 1,105 length if drawn to the same scale; it is therefore customary touse a different scale for the power ordinates, as in fig. 1,345. The illustration is lettered identical with fig. 1,344, wi
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