A Measurement of Frequency of Alternating Current Using Light-Emitting Diodes

Abstract

In the education of natural science in lower secondary school, it is an important study to make a distinction between direct and alternating electric currents through an experimentation or observation. On this account a simple method to measure the frequency of alternating current was devised. Light-emitting diode (LED) flashes with the same frequency as alternating current supplied. When a flash ing LED moves quickly, lighting spots are observed as a dashed line. In this experiment a LED was fixed on a disk which was turned by a motor. The turning speed was adjusted until the movement of lighting spots came to a standstill. At this stationary state the product of the number of lighting spots on the disk and the number of rotations per second is the frequency of the supplied current. For the measurement of rotation rate a special counting system effected by pushing the equal key of an electric calculator was applied. The pretty feature of lighting spots in this experiment is enough attractive for pupil and its demonstration effect as a teaching material is expected.