25 Mar, 2013
PRESENTATION: The current in which the magnitude and the sense vary cyclically is called alternating current. The kind of oscillation of the alternating current most commonly used is sinusoidal, because it achieves a more efficient transmission of the energy.
- Alternating-current demonstration using Christmas tree lights, John Carlson, Phys. Teach. 50, 315 (2012)
INTRODUCTION: In the first times of the electricity, the electrical energy was consumed in the proximity of the generator which produced it. That’s the reason why direct current was employed. But as it was necessary to transport the electric energy at some distance, the energetic losses made it necessary to take recourse to alternating current, which could, by means of transformers, transport the electricity to a high potential and then reduce it to the desired potential for its consumption.
In 1882, the physicist, mathematician, and inventor Nikola Tesla designed and constructed the first AC induction engine. The system used nowadays was fundamentally designed by Nikola Tesla, but the distribution of the alternating current was commercialized by George Westinghouse. During the decade of 1880, a heated debate took place between Edison and Westinghouse about the best way to distribute the electrical energy. Edison was in favour of the direct current (DC), which does not vary with the time: Westinghouse, of the alternating current (AC).
OBJECTIVE: To test the flickering of a neon lamp connected to the alternating current and the factors that influence it.
MATERIALS: neon lamp, resistance, electric cable, plug, soldering iron, tin.
SETUP: The cables of the neon lamp and the resistance must be welded to the wires of the line cable and carefully wrapped with tape or inside a AC power supply (a plug).
EXPLANATION: A neon lamp flickers at approximately 16 times per second (it will depend on the frequency of the alternating current applied to Spain, for instance, 50Hz), which makes these images imperceptible for the human eye. When the lamp turns circularly what we do is to trigger the stroboscopic effect, which in this case enables us to observe that flickering. So, after having performed the experiment, we observe that, for instance, at an angular velocity of 31,84 rad/s about 20 luminous intervals are observed.
CONCEPTS: alternating current, resistors, inductors, capacitors, resonance, angular velocity, resistance, intensity, voltage, power, frequency, period.
- R. Serway, Física, Mac Graw Hill, 2010.
- P. Tipler, Física para la Ciencia y la tecnología, Reverté, 2012.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2011-2012: Airas Toba, Cristina Varela, Bran Touriño
LINK pdf STUDENTS (In Spanish):