Wavelength frequency and energy of electromagnetic waves

Electromagnetic Radiation

EM radiation is a form of energy propagation where photons with both particle and wavelike properties travel at the speed of light.1 EM waves carry energy and transfer their energy upon interaction with matter. The energy associated with EM radiation is proportional to frequency and inversely proportional to wavelength. Thus, EM waves with shorter wavelengths have more energy. Examples of EM radiation (from lowest to highest energy) include radio waves, microwaves, infrared, visible light, UV, and radiographs (Fig. 3.1). EM radiation can be further divided into ionizing and nonionizing radiation. EM radiation at or below the UV spectrum is nonionizing, whereas radiographs are ionizing. Ionizing EM has enough energy to remove tightly bound electrons from an atom or molecule. The release of bound electrons leads to the generation of ions and free radicals. Within living cells, ions and free radicals interact with cellular machinery and cause DNA damage, which can ultimately lead to cell death. Radiotherapy uses ionizing radiation in order to cause damage to tumor cells. The photons used for therapeutic radiation generally have wavelengths of 10−11 to 10−13 m (see Fig. 3.1).1

Electromagnetic Radiation.

Electromagnetic radiation is an electric and magnetic disturbance traveling through space at the speed of light (2.998 × 108 m/s). It contains neither mass nor charge but travels in packets of radiant energy called photons, or quanta. Examples of EM radiation include radio waves and microwaves, as well as infrared, ultraviolet, gamma, and x-rays. Some sources of EM radiation include sources in the cosmos (e.g., the sun and stars), radioactive elements, and manufactured devices. EM exhibits a dual wave and particle nature.

Electromagnetic radiation travels in a waveform at a constant speed. The wave characteristics of EM radiation are found in the relationship of velocity to wavelength (the straight line distance of a single cycle) and frequency (cycles per second, or hertz, Hz), expressed in the formula

c=λv

where c = velocity, λ = wavelength, and v = frequency.

Because the velocity is constant, any increase in frequency results in a subsequent decrease in wavelength. Therefore, wavelength and frequency are inversely proportional. All forms of EM radiation are grouped according to their wavelengths into an electromagnetic spectrum, seen in Figure 1-3.

The particle-like nature of EM radiation manifests in the interaction of ionizing photons with matter. The amount of energy (E) found in a photon is equal to its frequency (ν) times Planck's constant (h):

E=νh

Photon energy is directly proportional to photon frequency. Photon energy is measured in eV or keV (kilo-electron volts). The energy range for diagnostic x-rays is 40 to 150 keV. Gamma rays, x-rays, and some ultraviolet rays possess sufficient energy (>10 keV) to cause ionization.

The energy of EM radiation determines its usefulness for diagnostic imaging. Because of their extremely short wavelengths, gamma rays and x-rays are capable of penetrating large body parts. Gamma rays are used in radionuclide imaging. X-rays are used for plain film and computed tomography (CT) imaging. Visible light is applied to observe and interpret images. Magnetic resonance imaging (MRI) uses radiofrequency EM radiation as a transmission medium (see Fig. 1-3).

Electromagnetic Radiations

Electromagnetic radiation is a type of energy that is commonly known as light. Generally, light travels in waves, and all electromagnetic radiation travels at the same speed, which is about 3.0 × 108 ms− 1 through a vacuum. Electromagnetic waves are produced by motion of electrically charged particles. The energy propagates as a wave such that the crest and troughs of wave move in a vacuum at a speed of 299 792 458 ms− 1. The many forms of these radiations appear different to the observer; light is visible to the human eye, but x-rays or radio waves are not. Some important characteristics of electromagnetic radiations are as follows:

These are produced by the oscillation of electric charge and magnetic field. The electric and magnetic components are mutually perpendicular to each other and are coplanar.

These are characterized by their frequencies or wavelengths or wave number.

All types of these radiations travel with the same velocity and require no medium for their propagation.

The energy of electromagnetic radiation is directly proportional to its frequency. The phenomenon of it was given by Planck known as Planck's law, E = hʋ.

When visible light (a region of electromagnetic radiations) is passed through a prism, it split up into seven colors. This phenomenon is known as dispersion (Figure 1).

Terms related to electromagnetic radiations:

Wavelength (λ): The distance between two adjacent crests or troughs in a particular wave. It can be expressed in angstrom unit or nanometer (1 Å = 10− 10 m and 1 nm = 10− 9 m).

Wave number (ῡ): It is the reciprocal of wavelength and is expressed in per centimeter. It is defined as the total number of waves that can pass through a space in 1 cm.

Frequency (ʋ): It is defined as the number of waves that can pass through a point in 1 s. It is expressed in cycles per second or in hertz (1 Hz = 1 cycle s− 1).

Energy (E): Energy of the particular radiation can be calculated by applying the relation E = hʋ = hc/λ, where h = Planck's constant = 6.626 × 10− 34 Js.

Table 1 shows the relationship among various parameters associated with electromagnetic radiations.

Table 1. Relation among various parameters associated with electromagnetic radiations

Electromagnetic Radiation

Electromagnetic radiation was first predicted in Maxwell's equations in 1864 and its existence was demonstrated by Heinrich Hertz in 1888. During World War II, microwave technology was used in radar telecommunications. The first microwave oven was developed by the Raytheon Company of North America in 1951, demonstrating the potential of microwaves in applications that provide rapid and energy-efficient heating. In the 1970s, the microwave generator was reengineered by the Japanese into a domestic microwave oven (a simple, reliable, and cheap magnetron) to be used in food processing.

Electromagnetic radiation is widely used in food processing and can destroy microorganisms in foods. In the past few years, the microwave or radio wave region of the electromagnetic spectrum has been explored for possible use in food processing with successful results in microbial inactivation. Various food-processing methods are based on use of electromagnetic radiation energy; the most commonly used are radiofrequency, microwave, infrared, ultraviolet, visible light, and irradiation. Electromagnetic radiation is classified according to the wavelength and consequently the depth of penetration into the food. Traditionally, the nonthermal effects of the application of electromagnetic radiation refer to lethal effects without a significant rise in temperature as in the case of ionizing radiation. One of the effects of such quantum energy is the breaking of chemical bonds. Roughly one electron volt of energy is required to break a covalent bond from a molecule to produce one ion pair, and this is referred to as a nonthermal effect. Electromagnetic radiation above 2500 × 106 MHz is mostly referred to as ionizing radiation. The ionizing radiation source could be an electron beam, x-rays (machine generated), or gamma rays (from Cobalt-60 or Cesium-137), and the energy of a gamma ray is above 2 × 10−14 J. If the wavelength of radiation increases, the frequency and the energy of radiation decrease. Thus, nonionizing radiation energy is not capable of breaking all the chemical bonds. Microwaves belong to the group of nonionizing forms of radiation. Thus, they do not have sufficient energy (2 × 10−24 – 2 × 10−22 J) to affect all chemical bonds. Therefore, the nonionizing radiation is the electromagnetic radiation that does not carry enough energy or quanta to ionize atoms or molecules, represented mainly by ultraviolet rays (UV-A, UV-B, and UV-C), visible light, microwaves, and infrared.

EMR and Heat Effects: Irreversible?

EMR has a negative effect on testicular function through the creation of reactive molecules, or oxidative stress, and the concomitant disruption of the testicular ability to detoxify those molecules. Interestingly, few studies have evaluated the possible protective role of vitamins C and E in the EMR-induced oxidative stress in the testes, which may involve facilitating the restoration of normal testicular tissue and function (Gorpinchenko et al., 2014).

We know that testicular tissue is highly sensitive to ionizing radiation. Doses in the range of 0.11–15 Gy may temporarily reduce sperm counts, while 2 Gy may result in long-lasting or permanent absence normal sperm and sterility (Rowley et al., 1974). At higher doses (> 15 Gy), the Leydig cells, in charge of production and secretion of testosterone, may be affected. In addition, whole body irradiation can damage the regulation of hormones in the Brain, affecting the reproductive capability. However, more studies are necessary to evaluate if the additive effects of EMR-emitting devices and nonionizing radiation in sperm counts are reversible or irreversible. None of the above-mentioned studies have evaluated prospectively the influence of EMR irradiation on paternity. Such investigations require long-term design and many previously healthy volunteers. At the present time nobody knows the real intercommunication between the constant direct mobile phones, computers, laptops, and Wi-Fi-emitted irradiation effects on testes and developmental delays in the offspring.

Electromagnetic Radiation

Electromagnetic radiation is a form of energy that propagates as both electrical and magnetic waves traveling in packets of energy called photons. There is a spectrum of electromagnetic radiation with variable wavelengths and frequency, which in turn imparts different characteristics. Examples of energy within the electromagnetic spectrum include x-rays (most widely clinically used to treat malignant lesions), visible light, infrared light, and radio waves (Fig. 13.2).

The energy of electromagnetic radiation is quantified by an electron volt (eV), where 1 eV describes the energy gained by an electron as it is accelerated through a potential difference of 1 volt. Electromagnetic radiation deposits energy in two forms as it passes through biologic material: excitation and ionization. Excitation describes the deposition of enough energy to raise an electron to a higher electron shell without ejection of the electron. However, ionizing electromagnetic radiation has enough energy to eject one or more electrons from the atom. X-rays and gamma rays, whose properties are equivalent, are clinically the most important form of ionizing electromagnetic radiation in the treatment of cancer.

Intranuclear production of ionizing radiation occurs when unstable atoms decay to more stable nuclides via beta minus decay, beta plus decay, or electron capture. These “gamma rays” are often produced from elemental sources that are used clinically for head and neck brachytherapy. Brachytherapy describes any procedure in which an elemental source of radiation is implanted or placed in close proximity to achieve therapeutic radiation delivery to a target. Teletherapy is the use of ionizing radiation delivered with no direct contact with the patient. Historically, teletherapy machines housed a source of cobalt-60; however, due to higher skin dose and the necessity to replace the source as it decayed, teletherapy machines have transitioned to extranuclear production of ionizing radiation (i.e., x-rays) using linear accelerators (linacs) (Fig. 13.3). A linac is a high-voltage electrical device that accelerates electrons to very high energies and aims them into a target in the linac gantry head, usually containing tungsten or gold. During the collision process, the kinetic energy of the electrons is converted to high-energy photons. Therapeutic external beam radiation x-ray energies generally range between kilo- and mega-electron volts (keV or MeV). The x-ray beams are narrowed and shaped with a collimator in the treatment machine head before delivery to the patient.

Electromagnetic Radiation and Light

Electromagnetic radiation is a traveling disturbance in space that comprises electric and magnetic components. Unlike the field associated with a common magnet or the earth, the magnetic field associated with electromagnetic radiation is constantly changing its direction and strength. The electric field component undergoes exactly the same behavior. Figure 1 illustrates what would be observed if it was possible to see the electric and magnetic components of a ray of radiation as it passes. It is the interaction of the electric and magnetic components of radiation with matter that are responsible for all the phenomena that are associated with radiation, such as human vision, sunburn, microwave cookery, radio and television, and of course spectroscopy.

There are some important fundamental features of electromagnetic radiation. The periodicity of the disturbance, or the distance between adjacent troughs or adjacent peaks, is referred to as the wavelength of the radiation. The number of times the electromagnetic field undergoes a complete cycle per unit time is called the frequency. The speed with which radiation can travel is limited, and moreover, radiation of all wavelengths travel at a single speed. This is referred to as the speed of light, universally denoted by the symbol c. The speed of light (and every other radiation) is dependent on the substance through which it travels, and reaches a maximum in a vacuum. The speed of light is a constant of proportionality between frequency and wavelength as described by the following equation:

c=νλ

where ν is the radiation frequency, λ is the radiation wavelength, and c is the speed of light.

The interpretation of this equation is that wavelength and frequency are related. Electromagnetic radiation of long wavelength must have a low frequency, whereas radiation of short wavelength must have a high frequency. At the long-wavelength (low-frequency) end of the electromagnetic radiation spectrum are radio waves, while at the other end is high-frequency (short-wavelength) radiation such as gamma rays. Between these extremes lie other forms of radiation, including microwaves, infrared (IR), ultraviolet (UV), and the narrow band of radiation that can be directly observed by humans, visible light.

Radiation carries energy with it, a phenomenon that is made use of in the domestic microwave oven, for example. The radiation is carried in small discrete quantities or ‘quanta’ (singular: ‘quantum’). The amount of energy carried in each quantum is proportional to the frequency of the radiation. As frequency and wavelength have an inversely proportional relationship, the energy quantum carried is inversely proportional to wavelength. Radiation of high frequency and short wavelength (e.g., x-rays, gamma rays), therefore, is of high energy, whereas low-frequency radiation that must have long wavelength (e.g., radio waves) carries little energy.

Electromagnetic Radiation

Electromagnetic radiation (x-rays and gamma rays) is indirectly ionizing. These types of radiation do not themselves produce chemical and biologic damage, but when they are absorbed in the medium through which they pass, they give up their energy to produce fast-moving electrons by the Compton, photoelectric, or pair-production processes (Fig. 1-1). X-rays and gamma rays are forms of electromagnetic radiation that do not differ in nature or properties; the designation of x or gamma reflects the way in which they are produced. X-rays are produced extranuclearly, which means that they are generated in an electric device that accelerates electrons to high energy and then stops them abruptly in a target, made usually of tungsten or gold. Part of the kinetic energy, or energy of motion of the electrons, is converted into photons of x-rays. Gamma rays are produced intranuclearly (i.e., emitted by radioactive isotopes); they represent excess energy that is given off as the unstable nucleus breaks up and decays in its efforts to reach a stable form.

Microwave and Radiofrequency Processing

Electromagnetic waves of certain frequencies generate heat in foods by dielectric and ionic mechanisms. Microwave and radiofrequency heating have the advantage that they require less time than conventional heating, particularly for solid and semisolid foods. Industrial microwave pasteurization has been used for at least 30 years, but not radiofrequency processing systems. Food does not heat uniformly during microwave processing, and this remains an important issue when considering this technology. Several methods have been used to improve the uniformity of heating but equipment design can significantly influence processing parameters and establishing general conclusions has proved difficult.

Electromagnetic Radiation

EMR is energy propagated through space at a fixed velocity, and EMR comprises a continuous spectrum of varying energies, ranging from gamma rays to radio waves. By convention, the terms photochemistry and photobiology are restricted to the effects of nonionizing radiation, including UVR, visible light, and infrared radiation, but omitting ionizing gamma rays and X-rays (Shea and Parrish, 1991). EMR can be modeled as a stream of discrete particles or packages of energy (quanta or photons), or with equal validity as waves of oscillating electrical and magnetic fields oriented transversely to each other and to the direction of propagation. Accordingly, EMR can be described by its quantum properties (energy per photon in electron volts) or wave properties (wavelength and frequency). The photobiology of skin is best understood with reference to both energy per photon and total energy striking the skin (usually expressed in joules per cm2).

Photobiologists subdivide UVR into discrete wave bands. Vacuum UVR (100–200 nm) is efficiently absorbed by the molecular nitrogen in air and therefore has little relevance to terrestrial photobiology. UVC (200–280 nm) is efficiently absorbed by the ozone layer of the stratosphere and therefore does not penetrate to the earth's surface; further deterioration of the ozone layer because of pollution may result in a biologically significant increase in the terrestrial UVR in the 280- to 290-nm wave band. Solar UVB (280–315 nm) does efficiently penetrate to the earth's surface and is responsible for most of the acute effects of sunlight on human skin, for example, erythema and delayed pigmentation. UVA (315–400 nm), also known as black light, is about 1000 times less efficient on a photon basis than UVB at inducing most of the acute photobiologic effects on skin. In addition to Sun, artificial sources of UVC, UVB, and UVA are increasingly significant for the health and appearance of human skin. More recently, intense UVA-emitting lamps have been widely used in tanning salons, under the assumption that, if UVA does not cause sunburn as effectively as UVB or UVC, it is considered to be ‘safe.’ Recently, however, UVA has been found to damage the skin by causing premature aging, nonmelanoma skin cancer, and melanoma (Ming et al., 2011a; Noonan et al., 2012).