Electromagnetic Spectrum

The orderly distribution of electromagnetic waves according to their wavelength or frequency is called the electromagnetic spectrum.

Electromagnetic spectrum covers a wide range of wavelengths (or) frequencies. The whole electromagnetic spectrum has been classified into different parts and sub parts, in order of increasing wavelength and type of excitation. All electromagnetic waves travel with the velocity of light. The physical properties of electromagnetic waves are determined by their wavelength and not by their method of excitation

Uses of electromagnetic spectrum

The following are some of the uses of electromagnetic waves:

Radio waves

Ø Radio waves are produced by the accelerated motion of charges in conducting wires.

Ø These waves are used in radio and television communication systems.

Ø AM band is from 530 kHz to 1710 kHz.

Ø Higher frequencies upto 54 MHz are used for short waves bands.

Ø Television waves range from 54 MHz to 890 MHz.

Ø FM band is from 88 MHz to 108 MHz.

Ø Cellular phones use radio waves in ultra high frequency (UHF) band.

Microwaves

Ø Microwaves (short-wavelength radio waves), with frequencies in the gigahertz (GHz) range, are produced by special vacuum tubes (called klystrons, magnetrons and Gunn diodes).

Ø Due to their short wavelengths, they are used in radar communication system.

Ø Microwave ovens are an interesting domestic application of these waves.

Infra-red waves

Ø Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the low-frequency or long-wave length end of the visible spectrum.

Ø Infrared waves are sometimes referred to as heat waves.

Ø Infrared lamps are used in physiotherapy.

Ø Infrared photographs are used in weather forecasting.

Ø As infrared radiations are not absorbed by air, thick fog, mist etc, they are used to take photograph of long distance objects.

Ø Infra-red absorption spectrum is used to study the molecular structure.

Visible light

Ø It is the most familiar form of electromagnetic waves. It is the part of the spectrum that is detected by the human eye.

Ø Visible light emitted or reflected from objects around us provides information about the world.

Ø The wavelength range of visible light is 4000 Å to 8000 Å.

Ultra−violet radiations

Ø The sun is an important source of ultraviolet light.

Ø They are used to destroy the bacteria and for sterilizing surgical instruments.

Ø These radiations are used in detection of forged documents, finger prints in forensic laboratories.

Ø They are used to preserve the food items.

Ø They help to find the structure of atoms.

X-rays

Ø Beyond the UV region of the electromagnetic spectrum lies the X-ray region.

Ø It covers wavelengths from about 10^–8 m (10 nm) down to 10^–13 m (10–4 nm).

Ø X-rays are used as a diagnostic tool in medicine.

Ø It is used to study the crystal structure in solids.

γ−rays

Ø They lie in the upper frequency range of the electromagnetic spectrum and have wavelengths of from about 10^–10m to less than 10^–14m.

Ø Study of γ rays gives useful information about the nuclear structure and it is used for treatment of cancer.