Types and Characteristics of Electromagnetic Radiation
– Radio waves
– Microwaves
– Infrared radiation
– Visible light
– Ultraviolet radiation
– Electromagnetic waves consist of synchronized oscillations of electric and magnetic fields
– They can travel at the speed of light in a vacuum
– The oscillations of the electric and magnetic fields are perpendicular to each other and to the direction of wave propagation
– The position of an electromagnetic wave in the spectrum is determined by its frequency or wavelength
– Different frequencies of electromagnetic waves have different names and effects on matter
Interaction of Electromagnetic Waves with Matter
– Electromagnetic waves are emitted by charged particles undergoing acceleration
– They can exert force on other charged particles
– EM waves carry energy, momentum, and angular momentum away from their source
– Electromagnetic radiation refers to EM waves that can propagate without the influence of the charges that produced them
– Near field refers to EM fields near the charges and current that directly produced them
Quantum Mechanics and Electromagnetic Radiation
– Electromagnetic radiation can be viewed as consisting of photons
– Photons are uncharged elementary particles with zero rest mass
– Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level
– Quantum effects can produce additional sources of EMR, such as electron transitions and black-body radiation
– The energy of a photon is quantized and increases with higher frequency
Effects of Electromagnetic Radiation on Matter
– Non-ionizing radiation includes visible light, infrared, microwaves, and radio waves
– Non-ionizing radiation does not have enough energy to ionize atoms or break chemical bonds
– Effects of non-ionizing radiation are primarily due to heating effects from the transfer of energy from multiple photons
– Ionizing radiation includes ultraviolet, X-rays, and gamma rays
– Ionizing radiation can cause chemical reactions and damage living cells beyond heating effects and can be a health hazard
Properties and Behavior of Electromagnetic Waves
– Electromagnetic waves are self-propagating transverse oscillating waves of electric and magnetic fields
– Electric and magnetic fields obey the properties of superposition, meaning they add together according to vector addition
– Coherent light waves can interact and yield a resultant irradiance through constructive or destructive interference
– Electromagnetic fields of light are not affected by static electric or magnetic fields in a linear medium like a vacuum
– In nonlinear media, interactions can occur between light and static electric and magnetic fields, resulting in effects like the Faraday effect and the Kerr effect
– Refraction occurs when a wave crosses from one medium to another, causing a change in its speed and direction
– The degree of refraction is determined by the ratio of refractive indices of the media and is summarized by Snell’s law
– Light of composite wavelengths disperses into a visible spectrum when passing through a prism due to the wavelength-dependent refractive index
– Different frequencies of light undergo different angles of refraction, leading to dispersion
– The speed of a wave changes as it crosses boundaries between different media, but its frequency remains constant
– Electromagnetic radiation exhibits both wave and particle properties
– Wave characteristics are more apparent when measuring over large timescales and distances
– Particle characteristics are more evident when measuring small timescales and distances
– The absorption of electromagnetic radiation by matter shows particle-like properties
– The observation of both wave and particle natures can be seen in experiments like the self-interference of a single photon
– Electromagnetic radiation is a transverse wave, where the electric and magnetic fields are perpendicular to the direction of wave propagation
– The electric and magnetic fields in an electromagnetic wave are in a fixed ratio of strengths to satisfy Maxwell’s equations
– In dissipation-less media, the electric and magnetic fields in an electromagnetic wave are in phase
– The frequency of a wave is its rate of oscillation and is measured in hertz
– Waves of the electromagnetic spectrum vary in size, from very long radio waves to very short gamma rays
– Electromagnetic waves in free space must be solutions of Maxwell’s electromagnetic wave equation
– Two main classes of solutions are plane waves and spherical waves
– Plane waves can be viewed as the limiting case of spherical waves at a very large distance from the source
– Both plane waves and spherical waves can have arbitrary time functions as waveforms
– Fourier analysis can be used to decompose the waveform of an electromagnetic wave into its frequency spectrum Source: https://en.wikipedia.org/wiki/Electromagnetic_wave
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. Types of EMR include radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays, all of which are part of the electromagnetic spectrum.
Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields. Depending on the frequency of oscillation, different wavelengths of electromagnetic spectrum are produced. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted c. In homogeneous, isotropic media, the oscillations of the two fields are on average perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength these are: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, and these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy, momentum, and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them, specifically electromagnetic induction and electrostatic induction phenomena.
In quantum mechanics, an alternate way of viewing EMR is that it consists of photons, uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic field, responsible for all electromagnetic interactions. Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of an individual photon is quantized and is greater for photons of higher frequency. This relationship is given by Planck's equation E = hf, where E is the energy per photon, f is the frequency of the photon, and h is the Planck constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light.
The effects of EMR upon chemical compounds and biological organisms depend both upon the radiation's power and its frequency. EMR of visible or lower frequencies (i.e., visible light, infrared, microwaves, and radio waves) is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules, or break chemical bonds. The effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are called ionizing radiation, since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, and can be a health hazard.
