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The Fifteen Watt Tungsten Lamp

Chapter 10: VIII. CURVES OF “OVERSHOOTING”.
By Clair Elmore Anderson
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Engineering & Technology

About This Book

A technical thesis investigates performance and behavior of a 15-watt tungsten electric lamp, presenting test methods, measurement apparatus, and empirical characteristic curves that relate candle power to voltage, current, resistance, and wattage. It reports life tests comparing constant-voltage, vibration-free conditions with severe mechanical shock, analyzes mean spherical candle power using Kennelley’s graphical method, and examines the overshooting phenomenon with proposed theories, quantitative measurements, and curve plots. Experimental limitations and sample-size caveats are acknowledged, and final conclusions synthesize the lamp’s efficiency, distribution patterns, and anomalous behaviors observed during testing.

VIII. CURVES OF “OVERSHOOTING”.

In order to prove that the law of resistances, namely, R = Ro(1 + αt) does not hold for the first instance after closing the switch on a tungsten lamp, the following curves have been plotted. Number V. has been taken from the oscillograph record shown in the first part of this paper and shows that about .024 second elapses before the current becomes normal. Knowing the current at any instant as given by this curve, it is easy to find the resistance at the same instant by Ohm's law, the electromotive force being a constant and known value. Curve VI shows this relation. Curves VII and VIII are approximate values and not absolute. Now from the temperature curve, values are taken and substituted in the formula for resistance, R = Ro(1 + αt), the resulting curve being Figure IX. It is seen that curves VI and IX do not take the same values at all until after a brief interval of time has elapsed. Curve VI is absolutely correct, however, as these values have been obtained from the oscillograph record. Consequently, the assumption upon which curve IX is based must be incorrect for the first .024th of a second and the conclusion is that the law of resistances does not hold. This result tends to strengthen the theory of the lag of resistivity for the “overshooting” of a tungsten lamp.

Fig V

Fig VI

Fig VII

Fig VIII

Fig IX
R = Ro[1 +αt]