History of electromagnetic waves

Perhaps the greatest theoretical achievement of physics in the 19th century was the discovery of electromagnetic waves. The first hint was an unexpected connection between electric phenomena and the velocity of light.

About 150 years ago, James Clerk Maxwell, an English scientist, developed a scientific theory to explain electromagnetic waves. He noticed that electrical fields and magnetic fields can couple together to form electromagnetic waves. Neither an electrical field (like the static which forms when you rub your feet on a carpet), nor a magnetic field (like the one that holds a magnet onto your refrigerator) will go anywhere by themselves. But, Maxwell discovered that a CHANGING magnetic field will induce a CHANGING electric field and vice-versa.

James Clerk Maxwell

An electromagnetic wave exists when the changing magnetic field causes a changing electric field, which then causes another changing magnetic field, and so on forever. Unlike a STATIC field, a wave cannot exist unless it is moving. Once created, an electromagnetic wave will continue on forever unless it is absorbed by matter.

Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and reception of radio waves. The unit of frequency of a radio wave -- one cycle per second -- is named the hertz, in honor of Heinrich Hertz. Hertz proved the existence of radio waves in the late 1880s. He used two rods to serve as a receiver and a spark gap as the receiving antennae. Where the waves were picked up, a spark would jump. Hertz showed in his experiments that these signals possessed all of the properties of electromagnetic waves.

Heinrich Hertz

With this oscillator, Hertz solved two problems. First, timing Maxwell's waves. He had demonstrated, in the concrete, what Maxwell had only theorized - that the velocity of radio waves was equal to the velocity of light! (This proved that radio waves were a form of light) Second, Hertz found out how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell's waves.

After Maxwell and Hertz, the next physicist who continued with the discovery of more developed magnetic waves, was Guglielmo Marconi. The Italian physicist began his experiments when he was barely 20, building on Heinrich Hertz's discovery of radio waves in 1888. In 1895 Marconi transmitted recognizable electronic signals from his family home in Pontecchio to a vertical raised antenna more than a mile away. As radio transmission of telegraph messages and, later, spoken words became more common and popular.Marconi also had the first transatlantic Morse code transmission from England to Newfoundland through electromagnetic waves.

Guglielmo Maconi

Fessenden's most notable achievements include the first audio radio transmission in 1900, the first two way transatlantic transmission in 1906 and the first broadcast of entertainment, also in 1906. Many of these were well ahead of their time, and showed his insight, not only into the technical aspects of radio, but also the commercial elements as well.

Reginald Fessenden

The next scientist to be moving to a more developed state was Philo T. Farnsworth who did the first all-electronic television broadcast., only at the age of 15. Philo T. Farnsworth was the first person to solve the problem of coordinating electronically scanned television cameras and electronically scanned television receivers that produced clear moving images.

Philo T. Farnsworth

Receiving television antennae pick up transmitted electromagnetic waves. Electronic circuits unscramble the electromagnetic signals and convert them back into electrical and audio impulses that mimic those originally sent out by the television camera and microphone systems. The video impulses travel to the picture tubes, which originally comprised electrical circuits and phosphor-covered screens divided into grids of pixels.

Edwin Armstrong is most commonly known for inventing frequency-modulated or FM radio in 1933. Frequency modulation or FM improved the audio signal of radio by controlling the noise static caused by electrical equipment and the earth's atmosphere.

Edwin Armstrong

Done by: Bleona Çoba