Electromagnetic spectrum

After the experimental discovery of electromagnetic waves by hertz in 1888, many other electromagnetic waves were discovered by different ways of excitation. The orderly distribution of electromagnetic radiations according to their wavelength or frequency is called the electromagnetic spectrum. Electromagnetic spectrum has a very wide range with wavelength variation from 10⁻¹³ m to 6*10⁶m. The whole electromagnetic spectrum has been classified into different parts and sub parts, in the order of increasing wavelength and according to the type of excitation. There is over lapping in certain parts of the spectrum, showing that the particular radiation can be produced by two methods. However, the physical properties of electromagnetic waves are determined by their wavelength and not by the method of excitation. The most commonly encountered portion of the electromagnetic spectrum is shown in figure. Which gives approximate wavelength and frequency ranges for the various segments. Only a small part of the complete electromagnetic spectrum (wavelength from 400nm to 700nm) is visible to human eye, as the radiations of this part can produce some sensation on the retina of the eye. This part of the spectrum is called visible spectrum. The radiations of different wavelengths in the visible part of the spectrum produce different colors on the retina of our eye.

The usual classification of electromagnetic spectrum is explained below.

1.       Radio waves: these are the electromagnetic waves of frequency of frequency range from few  Hz to 10⁹ Hz. These waves which are used in television and radio broad casting systems, are generated by electronic devices, mainly oscillating circuits having and inductor and capacitor.

2.       Microwaves: the wavelength of microwaves is greater than 1.0 mm and less than 30 cm. the frequency range of microwaves is 10⁹ Hz to 3.0*10¹¹ Hz. They are used for atomic and molecular research. These are used for aircraft navigation.

3.       Infra-red (IR) rays: the wavelengths range of infra-red rays is 1 nm and the frequency range is 3.08*10¹¹ Hz to 4.3*10¹⁴ HZ. These rays are used to keep the green house warm. These are used to treat muscular strains. The infra-red rays from the sun keep the earth warm.

4.       Visible light: the range of visible light is 400 nm (violet) to 700 nm (red) and the frequency range is 4.3*10¹⁴Hz to 7.5*10¹⁴ Hz. It is useful in optical microscopy and astronomy. Visible light is useful in photography.

5.       Ultra-violet (UV) rays: the range of ultra violet rays is 400 nm to 60 nm and their frequency range is 7.5*10¹⁴Hz to 5.0*10¹⁵ Hz. The sun important source of ultra-violet rays. They are used for sterilizing the surgical instrument. They are used in detecting the invisible writings, forged documents and finger prints.

6.       X-rays: the range of the wavelengths of x-rays varies from 60nm to 10⁻⁸ nm. The frequency of these rays varies from 5.0*10¹⁵ Hz to 3.0*10¹⁸ Hz. X-rays can penetrate through the human flesh but bones or metallic materials block these rays. These are used in radio therapy.

7.       Gamma- rays: the wavelength range of gamma-rays varies from 0.1 nm to 10⁻⁵ nm. The frequency of γ-rays is the highest of all the electromagnetic waves. The range of the frequency of γ-rays varies from 3.0*10¹⁸ Hz to 3.0*10²² Hz. Γ-rays are used in the treatment of cancer and tumors. It is also used to produce nuclear reactions.