Electromagnetic waves

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Electromagnetic waves

When the wave theory of light first gained general acceptance it was considered that light waves were conveyed through a transparent elastic medium which filled the whole of space, even a vacuum. This substance was called the ether. A further step forward was made in 1845, when Michael Faraday showed that, under certain conditions, light waves passing through a material medium were affected by a magnetic field. Now by that time, it was known that there was an inseparable connection between magnetism and electricity. Faraday’s experiment gave a strong hint that light might well have electrical properties.

Some years later, the eminent mathematician and physicist, James Clerk Maxwell, became very interested in Faraday’s work on electricity and eventually put forward a mathematical theory suggesting that an oscillating electric current should be capable of radiating energy in the form of electromagnetic waves (e.m. waves). An electromagnetic wave can be visualized as an oscillating electric force travelling through space accompanied by a similar oscillating magnetic force in a plane at right angles to it. More importantly, Maxwell’s equations led to the conclusion that such waves, if they existed, would travel with the same velocity as light. Some twenty years after the publication of Maxwell’s theory, the German scientist, Heinrich Hertz, showed that electromagnetic waves could indeed be produced by means of an oscillating electric spark. Moreover, he performed numerous experiments to demonstrate that the newly discovered waves underwent reflection, refraction, diffraction, and interference: in short, they behaved exactly like light waves but with a much greater wavelength.

Electromagnetic waves

Electromagnetic waves

The inference was that light waves themselves were also electromagnetic and
further experimental and theoretical studies have since confirmed this belief. More will be said on the subject after we have studied electricity. The work of Hertz was developed by Marconi and others who laid the foundations of our present-day use of electromagnetic waves in radio communication. Fig. 26.19 shows the whole range of electromagnetic waves in order of increasing wavelengths. Any particular range of wavelengths is referred to as a band. It will be noticed that the visible wavelengths occupy a very small band in the complete electromagnetic spectrum.

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Electromagnetic waves