Theory of Electromagnetic spectrum

Electromagnetic radiation is the transfer of energy at the velocity of light across free space or a solid medium in the form of electric and magnetic fields that make up electromagnetic waves like radio waves, visible light, and gamma rays. The intensity and frequency v of the time fluctuation of the electric and magnetic fields define an electromagnetic wave.

Theory of electromagnetism

Previously, the two terms, one is electricity and the other one is magnetism were regarded to be distinct properties . Maxwell, a Scottish physicist, devised a unique theory of electromagnetism in 1873. Electromagnetism is the process that  shows electrically charged particles affected by magnetic fields.

Electromagnetic interactions

The electromagnetic interactions are divided into four main categories:

• The square of the distance between electric charges determines the attraction or repulsion force between them.

• Poles of magnets are found in pairs and, like electric charges, attract and repel one another. 

• The current flowing through the wire generates a magnetic field whose direction is determined by the current’s direction.

• A magnetic field is created by an electric field which is in motion, and vice versa.

Generation of electromagnetic radiation- Mechanism

When a charged particle, like an electron, changes velocity—that is, when it is accelerated or decelerated—electromagnetic radiation is created. The charged particle transfers  the energy of the electromagnetic radiation created as a result of this process and forms a bundle of light energy, which is known as ‘Photon’.

The oscillating charge or current in a radio antenna is a common example of generation of electromagnetic radiation. The energy of a massless ‘light particle,’ known as a photon, is proportional to its frequency:

E=h x f

Where h is the Planck’s constant and f is the frequency, E is the energy of photon

h = 6.62607×10-34 Js

h = 4.13567x 1015 eVs.

Properties of Electromagnetic spectrum

There are three important properties of the electromagnetic spectrum. They are

• Wavelength 

• Frequency

• Amplitude

The separation between two sequential wave peaks is measured in wavelengths. This measurement is in metres (m).

The number of waves that develop in a particular amount of time is known as frequency. It’s usually expressed in hertz, which is the number of cycles per second (Hz) produced by the waves.

A shorter wavelength signifies a greater frequency since one cycle can flow in a shorter amount of time. Similarly, because each cycle takes longer to complete, a wavelength with longer waves has a lower frequency.

A wave’s amplitude, or vertical height, is half its peak-to-trough height; as the amplitude of a wave with a certain frequency rises, so does its energy.

Figure shows the Electromagnetic wave propagation direction of EM waves

On depiction of a wave, the length (λ), frequency (ν, labelled in Hz), and amplitude are all indicated in this figure

Electromagnetic spectrum

Electromagnetic radiation has a huge range of frequencies and wavelengths. The spectrum that is electromagnetic refers to this range. Based on the range of decrease in the wavelength and increase in the energy and frequency order, the electromagnetic spectrum is divided into seven areas. 

• Radio waves, 

• Microwaves, 

• Infrared (IR), 

• Visible light, 

• Ultraviolet (UV), 

• X-rays, and 

• Gamma rays.

X-rays and gamma are the radiation of  higher-energy, and are typically measured in terms of radiation per photon. Radio waves are typically described as  radiation with lower-energy,  in terms of frequency; Frequency is measured in cycles per second, or Hertz. Wavelength is measured in metres. Energy is measured in electron volt. Each of these three quantities for describing EM radiation are related to each other in a precise mathematical way.

Application of electromagnetic spectrum

There are various applications of the electromagnetic spectrum in day to day life. Some of them are,

• Radio waves: These are the EM waves that have lowest frequencies in the electromagnetic spectrum, with frequency up to 30 billion hertz (GHz) and wavelengths longer than 10 millimetres (0.4 inches). Radio is largely used for speech and data transmission, as well as entertainment media.

• Microwaves: EM spectrum between radio and infrared comes under microwaves. They have wavelengths ranging from about 9 to 10 mm (0.4 inches) to 100 micrometres (m), or 0.004 inches), with frequencies ranging from around 3 GHz to about 30 trillion hertz, or 30 terahertz (THz). Microwaves are utilised in radar, microwave ovens, high-bandwidth communications and industrial applications as a heat source. 

• Infrared waves: Infrared is a part of the electromagnetic spectrum that lies between microwaves and visible light. IR wavelengths range from 100 m (0.004 inches) to 0.00003 inches, with frequencies ranging from 30 THz to 400 THz. Although infrared waves are invisible to the naked eye, it can be felt as heat if the intensity is high enough. 

• Visible light: Between IR and UV, visible light is found in the middle of the electromagnetic spectrum. It has wavelengths of 740 nm to 380 nm and frequencies of 400 tetra hertz to 800 tetra hertz (.000015 inches). Visible light, in a broader sense, alludes to the wavelengths observable to the majority of human eyes.

• Ultraviolet light: Ultraviolet light is a part of the electromagnetic spectrum that lies between visible light and X-rays. It has wavelengths of about 381 nm to about 10 nm and frequencies of about 8 x1014 to 3×1016 Hz. It has a wide range of industrial and medical uses, yet it can harm tissue that is alive.

• X- rays: Soft and hard X-rays are the two types of X-rays, respectively. The area of the electromagnetic spectrum between UV and gamma rays is known as soft X-rays. The only distinction between them is their origin: speeding electrons make X-rays, while atomic nuclei produce gamma rays. X rays are used in medical applications.

• Gamma rays: Gamma rays are in the spectrum just above soft X-rays. Gamma-rays have wavelengths of less than 100 pm (4×109 inches) and frequency larger than roughly 10×1018 Hz. When delivered in carefully calibrated doses to limited areas, living tissue is harmed by gamma radiation,  making it beneficial for destroying cancer cells. Humans, on the other hand, are very vulnerable to uncontrolled exposure.

Conclusion

Radio waves, microwaves, X-rays, and gamma rays are all examples of electromagnetic (EM) radiation, which is found all around us. This content explains about the basic theory and concepts of electromagnetic spectrum, examples and application of electromagnetic spectrum.