On a macroscopic level, James Maxwell (1870) was the first to thoroughly analyse the interaction of charged substances and the activity of electrical and magnetic fields. He proposed that as an electrically charged particle accelerates, alternating electrical and magnetic fields are formed and transmitted. These fields are conveyed in waves known as electromagnetic waves or electromagnetic radiation.

Electromagnetic Radiations

Light is a kind of radiation that has been recognised from the beginning of time, and curiosity regarding its nature extends back thousands of years. Originally (Newton), the light was thought to be made up of particles only. However, it wasn’t until the nineteenth century that the wave nature of light was discovered. Maxwell was again the first to demonstrate that light waves had oscillating electric and magnetic properties.

Properties of Electromagnetic radiations

• The oscillating electric and magnetic fields generated by oscillating charged particles are perpendicular to one another and the wave’s propagation direction.
• Electromagnetic waves are different from sound or water waves. They do not need a medium to move and travel in a vacuum.
• It is now generally understood that several forms of electromagnetic radiation differ in wavelength (or frequency). This is what is known as the electromagnetic spectrum.
• Different names are given to different parts of the spectrum. Some examples include the radiofrequency region around 106 Hz, which is used for broadcasting; the microwave region around 1010 Hz, which is used for radar; the infrared region around 1013 Hz, which is used for heating; and the ultraviolet region around 1016 Hz, which is a component of the sun’s radiation. The tiny fraction about 1015 Hz is commonly referred to as visible light. Only this portion is visible to our sight (or detect). Non-visible radiation detection necessitates the use of specialised equipment.
• Electromagnetic radiation is represented using a variety of units.

These radiations are distinguished by frequency (ν) and wavelength(λ).

The SI unit for frequency (ν) is hertz (Hz, s-1). It is described as the number of waves that travel through a specific place in one second.

Wavelength must have length measures, and the SI units of length are metres (m). However, smaller units are utilised because electromagnetic radiation is made up of numerous types of waves with significantly lower wavelengths.

In a vacuum, all electromagnetic radiation, regardless of wavelength, moves at the same speed, 3.0 x 108 m/s. This is known as the speed of light, denoted by the letter ‘c.’

So, c = ν x λ

The equation connects frequency (ν), wavelength (λ), and light velocity (c).

The wavenumber is another extensively used term, particularly in spectroscopy. The number of wavelengths every unit length is its wavenumber. Its units are the inverse of the wavelength unit m-1. The most widely used unit, however, is cm-1.

Particle Nature of Electromagnetic Radiation

The wave aspect of electromagnetic radiation helps explain several experimental phenomena such as diffraction and interference. However, the following are some of the findings that could not be described by even the electromagnetic hypothesis of nineteenth-century physics:

• The nature of radiation emission from heated substances (black body radiation)
• The ejection of electrons from a metal surface when struck by radiation (photoelectric effect).
• Fluctuation of the solid’s heat capacity as a function of temperature
• Atom line spectra with specific reference to hydrogen

Max Planck’s description of the black body radiation phenomena is as follows: When solids are heated, they produce radiation over a wide variety of wavelengths. When an iron rod is fired in a furnace, it first gets dull red and gradually becomes redder and redder as the temperature rises. As the temperature rises, the radiation released becomes white, then blue as the temperature rises even higher. In terms of frequency, it indicates that the frequency of emitted radiation rises from a lower to a higher frequency when the temperature rises. The red colour belongs to the lower frequency area of the electromagnetic spectrum, whereas the blue colour belongs to the higher frequency sector. A black body is an ideal body that produces and absorbs radiations of all frequencies, and the radiation released by such a body is known as black body radiation.

Dual Behaviour of Electromagnetic Radiation

• Scientists were perplexed by light’s particle nature. Although it could adequately justify black body radiation and the photoelectric effect, it was inconsistent with the known wave behaviour of light, which might account for the phenomena of interference and diffraction. The only way was to embrace the concept that light has particle and wave-like features, i.e., light has dual behaviour.
• As per the experiment, light acts either as a wave or as a stream of particles.
• As radiation interacts with matter, it shows particle-like qualities instead of wave-like properties (interference and diffraction) when it propagates.
• This notion was completely foreign to the scientists’ understanding of matter and radiation, and it took researchers a long time to be convinced of its legitimacy.

Conclusion

Electromagnetic radiation is energy generated by the flow of electrically charged particles across a substance or vacuum or through oscillating magnetic and electric disturbances. The magnetic and electric fields intersect at 90 degrees, and the combined waves flow perpendicular to both the electric and magnetic oscillating fields that cause the disturbance.