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By carefully observing the wave motion of the water surface caused by a stone thrown into a pond, it is possible to ascertain that vibrating water particles have equal periods, because vertical movements of each oscillating particle are proportional to those of particles which are successively submitted to the same disturbance. In other words, oscillatory motion is isochronous as it is in pendulum clocks. Two particles that simultaneously reach the top of a wave crest are in phase; the distance between two crests is called wavelength, while the distance between the top of a crest and the underlying and supposedly stationary water surface is called amplitude of the oscillation. The time required by a particle to perform a complete oscillation is called period, while the number of oscillations in a second is called frequency.

As a consequence of this, and as anybody can although roughly observe on a water puddle, the longer is wavelength, the lower is frequency, and vice versa, high frequency always corresponds to short wavelength.

Sometime after the stone has fallen into the pond, wave motion gradually decreases from the centre to the periphery, producing damped waves. But if we throw a stone into the same point where the previous one had fallen, and then another one and so on, throwing objects of the same size, same weight (and applying the same strength) in a perfectly rhythmic and regular way, wave motion continues and produces continuous waves: we have thus created an oscillator.

spettro elettromagnetico

Now let’s throw two stones in the pond in two different points and in different times, and we will see another phenomenon: the oscillatory and concentric motion created by the fall of one of the objects will meet the motion created by the other, water ripples will become more complex and will interfere with one another, producing interference. “Echo” interference can be observed at the edges of a tub when we throw even only one pebble: waves that reach the edge produce other waves which, moving into the opposite direction, interfere with the previous ones.

Similar things, even though invisible, occur each time we produce a sound. Our vocal cords vibrate and produce oscillations of the surrounding air particles: these are sound waves that propagate in all directions, thus reaching those particular “resonators” represented by our ears. Once again, as it happened in the water pond, we are dealing with vibrations of material particles, made of air. But if we were surrounded by vacuum, no sound waves could be possible for lack of an oscillatory medium. However, oscillatory movements can also be generated in vacuum, not by material particles but by disturbances within an electric field, magnetic field and also gravitational field.

In physics the word field, which reminds us of a piece of cultivated land, refers to an area of space changed by the presence of an electric particle or a magnet or a material mass, which respectively create an electric, magnetic or gravitational field.

(Giancarlo Masini)


Entries related to Spettro Elettromagnetico in the Treccani Encyclopedia



Benvenuti nel sito ufficiale della Fondazione Guglielmo Marconi, istituita nel 1938.

Guglielmo Marconi (Bologna 1874 - Roma 1937) è colui che inventò la radiotelegrafia, ovvero la trasmissione di segnali a distanza senza l'ausilio di fili, il sistema che ancor oggi in tutto il mondo prende il nome di "wireless". Fece i primi esperimenti giovanissimo, nel 1894-1895, presso la casa paterna, Villa Griffone.

Sede della Fondazione Guglielmo Marconi è appunto Villa Griffone, la residenza di famiglia in cui Marconi realizzò i primi, decisivi esperimenti. Villa Griffone si trova a Pontecchio Marconi, a circa 15 km. da Bologna. La Villa è stata dichiarata Monumento Nazionale.

All’interno dello storico edificio è presente anche un Centro di ricerca ove operano specialisti della Fondazione Ugo Bordoni, dell’Università di Bologna e della stessa Fondazione Marconi, le cui attività quindi comprendono tre differenti aree – storia, ricerca, formazione – rendendo Villa Griffone meta di grande interesse per un vasto pubblico.



Welcome to the official site of Guglielmo Marconi Foundation, established in 1938.

The head office of Guglielmo Marconi Foundation is in Villa Griffone, the place where the Bolognese inventor began to develop the system of wireless telegraphy which then spread throughout the world.

Villa Griffone is located in Pontecchio Marconi, about 15 km from Bologna, Italy. The garden and the rooms of the villa are home to the Marconi Museum which is dedicated to the origins and development of radio communications. Villa Griffone is a National Monument.

A Research Center is also present inside the historical building, where researchers from the Ugo Bordoni Foundation, the University of Bologna and the same Marconi Foundation are intent on investigating in three different areas - history, research and training - making Villa Griffone a point of great interest for a wide audience.

see also museomarconi.it



© 2013 - Fondazione Guglielmo Marconi - Villa Griffone - via Celestini 1 - 40037 Pontecchio Marconi (BO) - C.F 80063250379

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