Electromagnetic Waves

In 1885, Hertz demonstrated experimentally, the existence of electromagnetic waves. Later on Marconi used these waves in establishing a communication between two locations at a distance of about 50 km, without the use of wires. Maxwell introduced the concept of displacement current and found that Ampere’s circuital law is logically inconsistent. To make Ampere’s circuital law consistent, Maxwell introduced the concept of displacement current, which is known as Ampere Maxwell’s law. Electromagnetic waves are those waves in which there are sinusoidal electric and magnetic field vectors varying perpendicular to each other as well as to the direction of propagation of wave. An accelerated charge acts as the source of electromagnetic waves. They do not require a material medium for their propagation. Electromagnetic Spectrum is the orderly distribution of electromagnetic radiations according to their wavelength or frequency. It has wide range with wavelength variation of 10-14 m to 6 x 102 m. The E.M. spectrum has been classified into different parts and subparts in the order of increasing wavelength or frequency. The physical properties of electromagnetic waves are decided according to their wavelengths. The spectrum consists of (i) radio waves which are used for different types of wireless communication, (ii) microwaves used in microwave ovens for cooking purpose, (iii) infrared rays or heat waves used in physiotherapy, (iv) visible rays which help us to see the colorful world, (v) ultraviolet rays used to detect fake currency and purify water, (vi) x- rays used for the detection of fractures, foreign bodies like bullets, diseased organs and stones in the human body and (vii) gamma rays used in the treatment of cancer and tumors.

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