Electromagnetic Radiation (EMR) and Electromagnetic spectrum

  • Definition: Electromagnetic radiation (EMR) is a form of “energy”, that consists of waves of the electromagnetic (EM) field, propagating through space, carrying electromagnetic radiant energy.
  • Electromagnetic radiation (EMR) is a form of energy that is produced by oscillating electric and magnetic disturbance, or by the movement of electrically charged particles traveling through a vacuum or matter.
  • Electromagnetic radiation is a combination of electric and magnetic fields that oscillate and propagate through space and carry energy from one place to another. Visible light is a form of electromagnetic radiation.
  • Electromagnetic radiation is the radiant energy released by the electromagnetic process. Electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillation of electric and magnetic field that travels with a speed of light (299,792,458 meters per second) through the vacuum.
  • The electric and magnetic fields come at right angles to each other and the combined wave moves perpendicular to both magnetic and electric oscillating fields thus the disturbance.
  • Electron radiation is released as photons, which are bundles of light energy that travel at the speed of light as quantized harmonic waves. This energy is then grouped into categories based on its wavelength in the electromagnetic spectrum. These electric and magnetic waves travel perpendicular to each other and have certain characteristics, including amplitude, wavelength, and frequency

The properties of Light of EMR can be explained by two theories;

  1. Corpuscular Theory
  2. Wave Theory
1. Corpuscular Theory
  • According to Newton, a source of light or a luminous body continuously emits tiny, massless (negligibly small mass) and perfectly elastic particles called corpuscles. They travel in straight lines in a homogeneous medium in all directions with the speed of light.
  • The corpuscles are so small that a luminous body does not suffer any appreciable loss of mass even if it emits light for a long time.
  • Light energy is the kinetic energy of the corpuscles. The sense of vision is produced, when the corpuscles impinge on the retina of the eye. The sensation of different colors was due to the different sizes of the corpuscles. On account of high speed, they are unaffected by the force of gravity and their path is a straight line. When the corpuscles approach a surface between two media, they are either attracted or repelled. Reflection of the particles is due to repulsion and refraction is due to attraction.
  • According to this theory, the velocity of light in the denser medium is greater than the velocity of light in the rarer medium. But the experimental results of Foucault and Michelson showed that the velocity of light in a denser medium is lesser than that in a rarer medium. Further, this theory could not explain the phenomena of interference, diffraction, and polarisation.
2. Wave Theory
  • According to wave theory, light/EMR travels in the form of waves. ((Consisting electrical and magnetic field)
  • All energies of the electromagnetic spectrum can be considered to be waves that move at the speed of light, with the types of radiation differing only in amplitude, frequency, and wavelength.
Characteristics Features of EMR
  • Product by the oscillation of electric charges and Magnetic field residing on the atom. E& B are mutually perpendicular to each other and are co-planar. (E- Electric Field, B-Magnetic field)
  • They are characterized by their wavelength or wave number or frequency.
  • The energy of an EMR is directly proportional to its Frequency.
  • The emission or absorption of radiation is quantized and each quantum of radiation is called Photon.
  • All types of EMR travel with the same velocity (speed of light0, no medium is required, it can travel through a vacuum.
  • When visible light passes through a prism, it is spilt into 7 colors and has a definite wavelength this is called Dispersion Phenomenon. So group of EMR can be spilt.

Fundamental Units

1. Wavelength
  • Wavelength is the distance from one wave crest to the next. Wavelengths can be measured in everyday units of length, although very short wavelengths have such small distances between wave crests that extremely short measurement units are required.
Kilometer (km) 1000 m
Meter (m) 1.0 m
Centimeter (cm)0.01 m = 10-2 m
Millimeter (mm)0.001 m = 10-3 m
Micrometer (um)a0.000001 m = 10-6 m
Nanometer (nm) = 10-9 m
Angstrom unit (A) = 10-10 m
Units of length used in remote sensing
  • This is the distance between two corresponding points on the wave and is measured In meters.
2. Frequency
  • Frequency is measured as the number of crests passing a fixed point in a given period of time.
  • Frequency is often measured in Hertz, units each equivalent to one cycle per second and multiples of the Hertz.
  • The number of cycles of a wave passing a fixed point per unit of time is measured in Hertz. (HZ)
3. Amplitude
  • Amplitude is equivalent to the height of each peak.
  • Amplitude is often measured as energy levels (formally known as spectral irradiance), expressed as watts per square meter per micrometer.


  • The electromagnetic spectrum is a bunch of EM waves arranged in the increasing order of their wavelength.
  • The electromagnetic spectrum is a collection of electromagnetic waves arranged according to frequency and wavelength.
  • The distribution of the continuum of all radiant energies can be plotted either as a function of wavelength or frequency in a chart known as the electromagnetic spectrum.
  • It ranges from shorter wavelengths (including X-rays and gamma rays) to longer wavelengths (microwaves and radio waves)
  • The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.
  • EMR extends over a wide range of energies or wavelengths or frequencies.
  • Electromagnetic waves form a continuous series in order of changing wavelength, frequency, and energy. This series is called the electromagnetic spectrum.
  • Electromagnetic waves are characterized by either frequency or wavelength, which
    determines the position in the electromagnetic spectrum which consists of radio waves,
    microwaves, infra-red waves, visible lights, Ultra violet rays, X-rays, Gamma rays

Electromagnetic waves are grouped into types that have similar wavelengths and so have similar properties.

Science Electromagnetic Spectrum diagram illustration
1. Radio
  • Your radio captures radio waves by radio stations, bringing your favorite tunes.
  • Radio waves are also emitted by stars and gases in space.
  • Radio waves are the lowest range of electromagnetic spectrum with a frequency of 30 Gigahertz and wavelength greater than 10 millimeters.
  • Radio waves are primarily used for communication including voice data.
  • Objects in space such as planets and comets, giant clouds of gas and dust, and stars and galaxies, emit light at many different wavelengths.
  • Some of the light they emit has a very large wavelength- sometimes as long as a mile. These long wavelengths are in the radio region of the electromagnetic spectrum. Radio waves travel at the speed of light, when passing through an object they are slowed according to that object’s permeability and permittivity.
2. Microwave
  • Microwave radiation will cook your popcorn in just a few minutes but is also used by astronomers to learn about the structure of nearby galaxies.
  • Microwaves fall in the range between radio and infrared waves.
  • They have a frequency of 3 GHz to 30 GHz and a wavelength of about 10 mm to 100 mm. They are used for high bandwidth communication, RADAR, and microwave ovens.
3. Infrared
  • Night vision goggles pick up the infrared light emitted by our skin. In space, infrared light helps us map the dust between stars.
  • Infrared falls between Microwave and Visible light range, they have a frequency range between 30 THz to 400 THz and wavelength of 100 µm to 740 nm.
  • IR light is invisible to human eyes but the heat intensity can be felt.
  • The basic applications of infrared get counted in the fields like military applications and civilian purposes.
  • Military applications include target acquisition, surveillance, night vision, homing, and tracking, non military uses include thermal efficiency analysis, environmental modeling, industrial facility inspection, remote temperature sensing, short-ranged wireless communication, spectroscopy, weather forecasting, etc.
4. Ultraviolet
  • Ultraviolet radiation is emitted by the sun and is the reason skin tans and burns. “Hot” objects in space also emit UV radiation.
  • Ultra-violet light is in the range between visible light and X-rays.
  • It has a frequency of about 8*1014 to 3 *1016 Hz and a wavelength of 380nm to 10nm.
  • It has been used for various medical and industrial applications.
  • UV wavelength of 320-400nm, called, UV-A, is responsible for the formation of Vitamin D by the skin, and on other hand causes sunburn and cataracts in the eyes.
5. X-ray
  • A dentist uses X-rays to image your teeth, and airport security uses them to see through your bag. Hot gases in the universe also emit X-rays.
  • An electromagnetic wave of high energy and very short wavelength, which is able
    to pass through much material opaque to light.
  • Maximum X-rays have a wavelength ranging from 0.01nm-10nm.
6. Gamma ray
  • Doctors use gamma rays in the treatment of dangerous diseases.
  • Gamma rays have a frequency greater than 1018 Hz and wavelengths less than 100
  • Gamma radiation causes damage to the tissues and can be used for curing cancer cells.
  • Gamma rays are the most energetic form of light and are produced by the hottest region of the universe.

Featured Image Credit – https://www.inspiritvr.com/general-physics/electromagnetic-radiation/electromagnetic-waves-study-guide

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