Electromagnetic wave

• Electromagnetic wave


  A disturbance of the electromagnetic field propagating in space, consisting of synchronized oscillations of electric and magnetic fields

  
• Electromagnetic radiation


  • Travels at the speed of light in a vacuum, c = 299,792,458 m/s
  • Upper limit for the speed at which conventional matter or energy can travel through space (according to special relativity)

  
• Electromagnetic wave propagation


  1. Electric field produces changing magnetic field

  2. Changing magnetic field produces changing electric field

  
• Photon


  Massless elementary particle that carries the smallest, indivisible quantum of energy of an electromagnetic wave
• Planck's relation


  E = hf, where E is the energy of the photon, h is Planck's constant, and f is the frequency of the wave

  
• Light is characterized by velocity (speed of light), wavelength, and frequency

  
• Light can be described as both a wave and a stream of photons

  
• Refractive index


  Ratio of the speed of light in a medium to the speed of light in a vacuum
• The human eye can only see a small part of the electromagnetic spectrum, with wavelengths between 380-780 nm

  
• Electromagnetic wave energy


  In a vacuum, the electrical and magnetic components of the energy carried are equal, while in a medium with non-zero electrical conductivity they are different

  
• Electromagnetic radiation (in order of increasing energy)

  • Radio
  • Microwave
  • Thermal
  • Infrared
  • Visible light
  • Solar
  • Laser
  • Ultraviolet
  • X-rays
  • Synchrotron
  • Gamma

  
• Natural sources produce electromagnetic radiation across the entire spectrum

  
• Visible light


  Electromagnetic radiation with wavelengths between approximately 400 nm and 700 nm, directly detected by the human eye

  
• Ultraviolet radiation


  Electromagnetic radiation with wavelengths from 10 nm to 400 nm, invisible to humans and with energies from 3 eV to 12.4 eV

  
• Ultraviolet radiation subdivisions


  • Ultraviolet A (UVA), 400-315 nm
  • Ultraviolet B (UVB), 315-280 nm
  • Ultraviolet C (UVC), 280-200 nm

  
• Ultraviolet radiation


  • Classified as ionizing radiation, able to detach electrons from atoms and molecules
  • The Sun emits ultraviolet over a wide range, but the Earth's atmosphere absorbs most of the short-wave part
  • Used in fluorescent lamps and chemical analysis (UV spectroscopy)
• Quantum theory of ultraviolet radiation

  Propagates in the form of energy quanta, with energy depending on wavelength and frequency

  
• Shorter wavelength and higher frequency ultraviolet radiation has greater energy and causes more biological and chemical effects

  
• Ultraviolet radiation subdivisions


  • UVA (400-315 nm, 3.10-3.94 eV)
  • UVB (315-280 nm, 3.94-4.43 eV)
  • UVC (280-100 nm, 4.43-12.4 eV)

  
• Effects of ultraviolet radiation on the human body

  • Regulates histamine formation in the skin
  • Causes photochemical erythema (reddening) of the skin
  • Produces vitamin D in the skin
  • Can damage DNA and cause skin cancer
• Photochemical erythema


  Reddening of the skin due to vasodilation, caused by ultraviolet radiation
• Factors affecting intensity of photochemical erythema: wavelength, radiation source intensity, irradiation time, distance from source, skin sensitivity

  
• Very high doses of ultraviolet radiation can cause irreversible damage and necrosis of the skin
• Latency period


  Time between ultraviolet exposure and onset of first erythema symptoms
• Ultraviolet radiation has therapeutic uses, but requires careful dosage to avoid harmful effects
• Wavelengths


  297 nm and 250 nm

  
• Factors affecting the intensity of photochemical erythema

  • Wavelength of ultraviolet radiation
  • Emission intensity of the radiation source
  • Irradiation time
  • Distance of the skin from the radiation source
  • Sensitivity of the skin

  
• Skin sensitivity factors


  • Thickness of the epidermis
  • Area of the body
  • Skin complexion and age
• Very high doses of ultraviolet radiation can cause irreversible damage to epidermal cells and even the dermis (necrosis)
• Latency period


  Time that elapses from exposure to ultraviolet rays to the onset of the first symptoms of erythema
• During the latency period, substances are produced which then undergo free secretion from the cells and reach the highest concentration in the phase of maximum erythema severity
• Latency period duration


  Depends on the dose, the wavelength of ultraviolet radiation and individual sensitivity
• Genetic damage from UV-C light

  • DNA absorbs UV-C light, and the absorbed energy can break bonds in the DNA
  • Most of the DNA breakages are repaired by proteins present in the cell's nucleus but unrepaired genetic damage of the DNA can lead to skin cancers
• Photochemical properties of ultraviolet radiation

  • Chemical reactions occurring under the influence of light
  • Can cause the formation of new compounds
  • Photosynthesis
  • Oxidation or reduction
  • Photolysis - the breakdown of a given compound into compounds with a less complex structure
  • Photoisomerization - the formation under the influence of light of compounds with an analogous molecular summary formula, but with different structure and different physical and chemical properties
• Vitamin D


  • Vitamin D3 in humans is absorbed through the skin
  • Vitamin D can be obtained by irradiation of plant and animal products with ultraviolet rays, but this requires great caution, because too intensive irradiation leads to the production of sterols with toxic properties, the so-called toxisterols
  • The active substance responsible for the absorption and transformation of calcium is not directly vitamin D3 (cholecalciferol), but its metabolite 25-hydroxycholecalciferol (25-HCC) which undergoes further hydroxylation in the kidneys to 1,25-Dihydroxycholecalciferol (1,25-DHCC; 1,25(OH)2D) which is the substance that improves the absorption of calcium in the intestines and its activation in the bones
• Increased sensitivity to ultraviolet radiation

  • The action of chemical compounds that increase sensitivity to ultraviolet radiation consists in causing periodic biological effects in the body that do not normally occur when exposed to radiation of a given wavelength
  • The sensitivity-increasing compound is not directly involved in these reactions, but is only a conveyor of energy to the components of the reaction
  • These reactions occur in the presence of oxygen

  
• UVC rays are the highest energy, most dangerous type of ultraviolet light, and little attention has been given to them in the past since they are filtered out by the atmosphere, but their use in equipment such as pond sterilization units may pose an exposure risk
• Bactericidal effect of ultraviolet rays

  • Exhibit ultraviolet rays with a wavelength of 250 to 270 nm, of which the most active is radiation with a wavelength of about 254 nm
  • Bactericidal action is conditioned by the absorption of sufficient energy by bacteria
  • As a result of photochemical reactions, there are changes in the structure of bacterial proteins and inhibition of their vital processes
• UVA, UVB and UVC can all damage collagen fibers and thereby accelerate aging of the skin
• Both UVA and UVB destroy vitamin A in skin which may cause further damage