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An accelerating charge is a source of an electromagnetic wave. The electromagnetic wave originates when an oscillating charge is taken. This charge produces an oscillating electric field in its neighbourhood. This field, in turn, produces an oscillating magnetic field in the neighbourhood. The process continues because the oscillating electric and magnetic fields act as sources of each other. Hence, an electromagnetic wave originates from the oscillating charge.

Source of electromagnetic waves:

The electric field is produced by stationary charges. Positive charges accelerate in the direction of the electric field and negative charges accelerate in the direction opposite to the direction of the electric field.

The Magnetic field is produced by moving charged particles. Because of moving charges, a force is exerted on the other moving charges. The force on these charges is always perpendicular to the direction of velocity and magnetic field.

Electromagnetic waves are produced when an oscillating charge is taken. This oscillating charge produces an oscillating electric field, which, in turn, produces an oscillating magnetic field. As both electric field and magnetic field are perpendicular to each other, they form an electromagnetic wave that is travelling perpendicular to both electric and magnetic fields.

Graphical representation of a linearly polarized electromagnetic wave:

A plane electromagnetic wave propagating along the z-direction. The electric field Ex is along the x-axis, and varies sinusoidally with z, at a given time. The magnetic field By is along the y-axis, and again varies sinusoidally with z. The electric and magnetic fields Ex and By are perpendicular to each other, and the direction z of propagation.

A linear polarized electromagnetic wave, propagation in the z-direction.

James Clerk Maxwell predicted the existence of electromagnetic radiation, while Heinrich Hertz tested a successful experiment to conclusively prove the existence of electromagnetic waves.

Electromagnetic spectrum:

The electromagnetic spectrum is the range of spectrums of electromagnetic radiation and their respective wavelengths. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from 1 Hertz to above 1023 Hertz, and wavelengths ranging from the size of a nucleus to 108 m.

Spectrum is divided into various regions which do not have sharp defined boundaries.

We can classify the different regions of the electromagnetic spectrum based on frequencies and wavelength as:

  1. Radio waves
  2. Microwaves
  3. Infrared waves
  4. Visible rays
  5. Ultraviolet waves
  6. X-rays
  7. Gamma rays

We will briefly discuss the different regions of the electromagnetic spectrum and also discuss their practical applications:

  1. Radio waves:

Radio waves are electromagnetic radiations that range within the frequency range of 500 kHz to 1000 MHz. The wavelength lies in the range of 1 mm to several hundred metres. Radio waves have the longest wavelength and lowest frequency compared to all EM waves.

Application of Radio waves:

  1. Radio Broadcasting: 

Radio broadcasting is one of the primary applications of radio waves. Here first, The signal is modulated using various Modulation devices like frequency modulation (FM) and amplitude modulation (AM). The modulated signal is encrypted and transmitted with the help of a radio transmitter. At the receiver side, the modulated signal can be decrypted.

  1. Cellular networks:

As radio waves are proficient in penetrating through rigid materials, this property allows companies an opportunity to use radio waves in the communication industry for the cellular link.

  1. Satellite communication:

As radio waves can travel large distances and are also penetrating rigid materials, this property is utilised for communication with the help of communication satellites. The radio wave containing information is transmitted by sending waves to the radio wave Detectors on satellites which receive and transmit signals to the station.

There are many other uses of radio waves in our daily life like RADAR, radio astronomy, remote control toys, etc.

  1. Microwaves:

Microwaves are produced by oscillating currents in special vacuum tubes like Klystrons, Magnetrons and Gunn diodes. Microwaves are the e.m waves having wavelength next smaller to radio waves, their frequency lies between 109Hz to 1012Hz. Due to their shorter wavelengths, they can travel as a beam in a signal.

Applications:

  1. It is used for the analysis of fine details of molecular and atomic structure.
  2. Since=310-2 mmicrowaves are useful for the demonstration of all wave properties on a macroscopic scale.
  3. The IRA-1E satellite launched by an Indian space research organization for communication and navigation uses microwave radiation to transmit signals to the receiver.

Also, there are many areas in the field of Biomedical, remote sensing where microwave radiation is used.

  1. Infrared waves:

The Infrared waves are produced by hot bodies and molecules. They are sometimes referred to as heat waves. To maintain the average temperature of the earth’s greenhouse gases, infrared waves play an important role. Waves are captured by these greenhouse gases in the atmosphere to raise their temperature and parallel the atmosphere.

Applications:

  1. Useful for elucidating molecular structure of various elements.
  2. Less scattered than visible light by atmospheric particles. So, useful for haze photography.
  3. Most remote controls operate by infrared pulses. In electronic devices like TV remotes, DVD players, projectors, etc. Infrared is often used to send signals through fibre optic cables for transmitting audio to sound systems and for high-speed internet connections.

  1. Visible rays:

It’s part of the spectrum that is detected by human eyes. Its wavelength ranges from about 700 nm to 400 nm. Our eyes are sensitive to this range of wavelengths. Different animals are sensitive to different ranges of wavelengths. For example, snakes can detect infrared waves.

Application:

  1. Detected by stimulating nerve endings of the human retina.
  2. Can cause a chemical reaction.

  1. Ultraviolet rays:

Ultraviolet waves cover wavelengths ranging about 400 nm (4×10-7 m) – 0.6 nm (6×10-10 m) falls lower to the wavelength range of X-rays and higher to the wavelength range of visible light.

Application:

  1. Ultraviolet waves can cause many chemical reactions. For example, the tanning of the human skin.
  2. Ionized atoms in the atmosphere, resulting in the ionosphere.

  1. X-rays:

Beyond the UV region of the electromagnetic spectrum lies the X-ray region. It covers wavelengths from about 10-8 m (10 nm) to 10-13 (10-4 nm).

Application:

X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer. Because X-rays damage living tissues, care must be taken to avoid over exposure.

  1. Gamma rays:

Gamma rays are electromagnetic radiations of the highest frequency range and lowest wavelength range. These are the most penetrating electromagnetic waves.

Application:

  1. In radiotherapy for the treatment of malignant tumours, gamma rays are used.
  2. To study the structure of atomic nuclei, gamma rays penetrate the atoms.

Conclusion:

Accelerated charge particles radiate electromagnetic waves. Electric and magnetic fields oscillate sinusoidally in space and time in an electromagnetic wave. The oscillating electric and magnetic fields, E and B are perpendicular to each other, and to the direction of propagation of the electromagnetic wave. There are many uses of the electromagnetic wave in the field of defence, navigation, the medical sector, and many fields.