Electromagnetic radiation in physics or chemistry describes the form of energy that is transmitted through space at an enormous velocity. Each type of electromagnetic radiation has both the properties of waves and particles.

Gamma rays, x-rays, ultraviolet (uv), visible, infrared (ir), microwave, and radio frequency are examples of electromagnetic radiation which contain a definite region of the spectrum. We used wavelength and frequency to describe different types of electromagnetic spectrum radiation.

## Electromagnetic wave

An electromagnetic wave has electric and magnetic components. The two components in electromagnetic radiation oscillate in the plane perpendicular to each other.

From the above picture, the vector representation of electromagnetic waves moving along the x-axis. The electric field varies in the direction of the y-axis and the magnetic field H varies in the direction of the z-axis. The velocity of electromagnetic waves in a vacuum is independent of frequency.

In comparison to other wave phenomena such as sound, the electromagnetic wave does not require any supporting medium for its transmission. An electromagnetic wave can be characterized by the following parameters such as wavelength, frequency, wavenumber, and velocity.

The wavelength of electromagnetic radiation is the distance between two successive maxima of an electromagnetic wave. It is denoted by the Greek letter Lambda (Î»). The usual units of wavelength vary with the region of electromagnetic spectrum radiation.

The more commonly employed units of wavelength are meter (m), centimeter (cm), millimeter (mm), micrometer (Î¼m), nanometer (nm), and angstrom.

 1 Î¼m 10âˆ’4 cm 10âˆ’3 nm 10âˆ’6 m 1 nm 10âˆ’6 Î¼m 10âˆ’7 cm 10âˆ’9 m 1 Ã… 10âˆ’8 cm 0.1 nm 10âˆ’10 m

The number of complete wavelengths passing through a given point in unit time is called the frequency of electromagnetic radiation. It is denoted by the Greek letter Î½. Frequency is the unit of reciprocal of time.

The frequency of electromagnetic radiation is generally expressed by cycles per second or Hertz (Hz) or Fresnel. By their definitions, wavelength and frequency are inversely proportional to each other.

 1 Hz 1 cycle sâˆ’1 1 Fresnel 1012 Hz 1 MHz 103 kHz 106 Hz

### Wavenumber

Frequency is more fundamental than the wavelength of electromagnetic waves. It is defined as the number of waves per centimeter in a vacuum. Mathematically, wavenumber = 1/wavelength (Î»). The wavenumber is generally used in infrared spectroscopy.

### Velocity of electromagnetic waves

The velocity is dependent on the medium through which radiation passing. It has the unit of cm sâˆ’1 or m sâˆ’1.

The product of wavelength and frequency of electromagnetic radiation is equal to the velocity of the wave in the medium. Therefore, wavelength (Î») Ã— frequency (Î½) = velocity (c).

When the density of the medium through which electromagnetic radiation passes decreases, the velocity, and wavelength of radiation increase. It reaches the maximum or constant value in a vacuum. Therefore, electromagnetic waves in a vacuum travel with a constant velocity of 3 x 108 m sâˆ’1.

## Electromagnetic energy

The wave nature of electromagnetic radiation fails to explain the phenomena like photoelectric effect. To explain such phenomena, it is assumed that electromagnetic radiation contains a stream of discrete particles of pure energy. These streams of discrete particles are called photons or quanta.

According to Planck’s quantum theory, the energy of the photon is proportional to the frequency of radiation. Electromagnetic energy is given the relationship,
E = hÎ½
where Î½ = frequency of electromagnetic radiation
h = Planck constant = 6.62607004 Ã— 10âˆ’34 m2 kg/s.

A higher frequency of radiation shows greater photon energy. Therefore, x-rays are more energetic than the rays obtained from visible light.

Gamma rays, x-rays, ultraviolet, visible, infrared, microwave, and radio waves are examples of electromagnetic radiation which contain a definite region of the spectrum.

Gamma rays are the shortest and most energetic waves in electromagnetic radiation. The main ways for the formation of gamma rays are nuclear fusion and nuclear fission reactions. Most of the gamma waves are generated by nuclear explosions, lighting, and the radioactive decay of substances.

Gamma rays are harmful radiation due to their high penetrating power. It can damage the bone marrow and internal organs of living organisms. Gamma rays are used mainly to sterilize medical equipment, tracers in medicine, and kill cancerous cells in radiotherapy.

X-rays are the type of electromagnetic radiation which absorbed or emitted by the movement of electrons close to the nuclei of relatively heavy atoms. Energetically, it is similar to radio waves, microwaves, visible light, and gamma rays.

It has enough energy to break down the molecules of living cells. X-rays are used mostly for medical imaging for the detection of bone fractures.

Ultraviolet radiation is non-ionizing radiation obtained mostly from the sun and other sources like mercury vapor lighting, fluorescent, and incandescent lights. It is beneficial for our health because uv radiation from the sun produces vitamin D.

Visible radiation or visible light is the form of waves with wavelengths between 400 to 750 nm. The approximate colour of visible light with their corresponding wavelength are given below the table,

 Colour Wavelength (nm) Violet 400 – 450 Blue 450 – 500 Green 500 – 570 Yellow 570 – 590 Orange 590 – 610 Red 610 – 750

Visible light radiation is used mostly in photography and illumination. In optical fiber communication technology, we also used visible types of radiation transmitted through glass fiber.

Infrared radiation (IR) is a region of the electromagnetic spectrum where wavelengths lie between the visible and microwave region. The infrared waves are longer than that of visible light but shorter than that of the microwave.

Infrared radiation can be subdivided into three regions,

1. Near-infrared
2. Mid-infrared
3. Far-infrared

All the three sub-regions of infrared are part of the electromagnetic spectrum associated with the changes in the vibration of the molecules.

Infrared waves are used mostly in communication technology, spectroscopy, and astronomy. In spectroscopy, it is used for the structure determination of inorganic or organic molecules. It is also used as a source of heat energy in medical and different types of industrial production.