Electromagnetic Radiation

Electromagnetic radiation (EMR) is a kind of radiation in which electromagnetic (EM) field waves carry radiant energy through space. Electromagnetic radiation includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. The electromagnetic spectrum consists of all these frequencies. Electromagnetic waves are produced when electric particles are accelerated, interacting with and exerting force on other charged particles. Energy, momentum and angular momentum can all be transferred from a source particle to the substance it interacts with. 

Electromagnetic radiation definition

Electromagnetic radiation has traditionally been understood as comprising electromagnetic waves, synchronised oscillations of electric and magnetic fields. 

When an electric or magnetic field changes regularly, electromagnetic radiation, also known as electromagnetic waves, is produced. Different wavelengths of the electromagnetic spectrum are produced depending on how this periodic change occurs and the generated power. 

Electromagnetic waves travel at the speed of light in vacuum, commonly represented by the letter “c”. Therefore, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy. Wave propagation is homogeneous, isotropic media, forming a transverse wave.

According to quantum mechanics, EMR comprises photons, which are uncharged elementary particles with zero rest mass and are the quanta of the electromagnetic field, responsible for all electromagnetic interactions. 

Quantum electrodynamics is a theory that describes how electromagnetic radiation interacts with matter at the atomic level. EMR can also be caused by quantum effects such as electron transitions to lower energy levels in an atom and black-body radiation. 

A single photon’s energy is quantized and increases with frequency. Planck’s equation E = hf expresses this relationship, where E is the energy per photon, f is the photon’s frequency, and h is Planck’s constant. A single gamma-ray photon, for example, may have 100,000 times the energy of a single visible light photon.

James Maxwell derived the waveform of the electric and magnetic equations, revealing the wave-like nature and symmetry of electric and magnetic fields. 

Maxwell concluded that light is an EM wave because the speed of EM waves predicted by the wave equation coincided with the measured speed of light. Heinrich Hertz’s experiments with radio waves confirmed Maxwell’s equations. 

Maxwell reasoned that because much of physics is symmetrical and mathematically artistic in some ways, there must be a symmetry between electricity and magnetism. 

Light, he realised, is a combination of electricity and magnetism, and the two are inextricably linked. According to Maxwell’s equations, a changing magnetic field is always associated with a spatially varying electric field.

Properties of Electromagnetic radiation

Electrodynamics studies electromagnetic radiation, whereas electromagnetism is a physical phenomenon related to electrodynamics theory. Both electric and magnetic fields exhibit superposition properties. 

As a result, a field caused by a specific particle or a time-varying electric or magnetic field contributes to other areas in the same space. Furthermore, because magnetic and electric field vectors are vector fields, they add up similarly. 

In optics, for example, two or more coherent light waves may interact and produce a resultant irradiance that differs from the sum of the component irradiances of the individual light waves due to constructive or destructive interference.

Light’s electromagnetic fields are unaffected by travelling through static electric or magnetic fields in a linear medium, such as vacuum. However, in nonlinear media, such as some crystals, interactions between light and static electric and magnetic fields can occur; these interactions include Faraday and Kerr.

When a wave refracts from one medium to another medium of different density, its speed and direction change as it enters the new medium. Snell’s law expresses the degree of refraction as the ratio of the media’s refractive indices. 

When the light of composite wavelengths (natural sunlight) passes through a prism, it disperses into a visible spectrum due to the prism material’s wavelength-dependent refractive index (dispersion); that is, each component wave within the composite light is bent differently.

At the same time, EM radiation has both wave and particle properties (see wave-particle duality). Therefore, many experiments have been carried out to confirm the existence of wave and particle properties. 

Wave characteristics are more visible when measuring EM radiation over relatively large timescales and distances, whereas particle characteristics are more visible when measuring over small timescales and distances. 

When electromagnetic radiation is absorbed by matter, for example, when the average number of photons in the cube of the relevant wavelength is significantly less than one, particle-like properties emerge. 

When light is absorbed experimentally, it is not difficult to observe non-uniform deposition of energy; however, this alone is not evidence of “particulate” behaviour. Instead, it reflects the quantum nature of matter.

When wave and particle effects are combined, the emission and absorption spectra of electromagnetic radiation are fully explained. The nature of the absorption and emission spectrum is determined by the matter composition of the medium through which the light travels. 

These bands correspond to the atoms’ permitted energy levels. Dark bands in the absorption spectrum are caused by particles in the medium between the source and the observer. The atoms absorb specific light frequencies, emitting them in all directions between the emitter and the detector/eye. 

As a result of the scattered radiation from the beam, a dark band appears on the detector. Dark bands in the light emitted by a distant star, for example, are caused by atoms in the star’s atmosphere. 

When a gas emits light due to atom excitation caused by any mechanism, including heat, it is referred to as emission.

Conclusion

The electromagnetic field can be viewed as a smooth, continuous field that propagates in a wave-like manner from a classical perspective in the history of electromagnetism. 

This field is quantized, which means that the effects of the free quantum field (i.e., non-interacting field) can be expressed in energy-momentum space as the Fourier sum of creation and destruction operators. In contrast, the effects of the interacting quantum field cannot.

 On the other hand, Electromagnetic ionising radiation refers to high-frequency ultraviolet, X-ray, and gamma-ray photons that have enough energy to ionise molecules or break chemical bonds. These radiations, which pose a health risk, can cause chemical reactions and damage living cells in ways that simple heating cannot.