This year (1997) there are two anniversary related to Galileo Ferraris. In fact, this Italian scientist, professor in Turin, was born in 1847 and died in 1897. He studied optics, acoustics and several fields of electrotechnics, but the most important discovery was the Rotating Magnetic Field that he applied for the first induction motor (with 4 poles) in 1885. Nowadays this kind of motors are the most used electric engines.
The induction motors use three-phase currents, that are generated by three tensions with a phase displaced of 120 degrees. These currents, feeding opportunely three static windings, produce a rotating magnetic field similar to the one created by a rotating magnet: the electromagnetic induction law states that a sinusoidal variation of the current in a coil generates a sinusoidal variation in the linkage and the three linkages, conveniently superimposed, cause the total magnetic field to rotate as you can see in the applet above.
Red, green and blue arrow are the displaced linkages, while the white arrow is the rotating magnetic field.
In the next Issue Science History will be
while Weekly Applet will be