P12 - Electromagnetic Waves

• Electromagnetic waves

  Transverse waves that transfer energy from the source of the waves to an absorber
• Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air
• Groups of electromagnetic waves


  • Radio waves
  • Microwaves
  • Infrared radiation
  • Visible light (red to violet)
  • Ultraviolet
  • X-rays
  • Gamma rays
• Our eyes only detect visible light and so detect a limited range of electromagnetic waves
• Different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength
• Refraction is due to the difference in velocity of the waves in different substances
• Radio waves


  Can be produced by oscillations in electrical circuits, and when absorbed may create an alternating current with the same frequency as the radio wave itself
• Changes in atoms and the nuclei of atoms


  Can result in electromagnetic waves such as Gamma rays being generated or absorbed over a wide frequency range
• Gamma rays

  Originate from changes in the nucleus of an atom
• Ultraviolet waves, X-rays and gamma rays


  • Can have hazardous effects on human body tissue as they are ionising radiation.
  • The effects depend on the type of radiation and the size of the dose
• Radiation dose

  Measure of the risk of harm resulting from an exposure of the body to the radiation (1000 millisieverts (mSv) = 1 sievert (Sv))
• Ultraviolet waves


  • Can cause skin to age prematurely
  • Increase the risk of skin cancer
  • Blindness
  • Cataracts
• 1. rays and gamma rays


  • Are ionising radiation that can cause the mutation of genes and cancer
• Practical applications of electromagnetic waves

  • Radio waves - television and radio communications
  • Microwaves - satellite communications, cooking food
  • Infrared - electrical heaters, cooking food, infrared cameras
  • Visible light - fibre optic communications, photography
  • Ultraviolet - energy efficient lamps, sun tanning
  • X-rays - Medical imaging
  • Gamma rays - Treating cancer and sterilising surgical equipment
• Higher the frequency and amplitude of the wave


  The greater the energy of the wave
• Gamma rays and X rays have the highest energy as they have the highest frequency in the EM spectrum
• Radio waves have the lowest energy, lowest frequency and highest wavelength
• Gamma rays have the highest energy, highest frequency and lowest wavelength
• Ionising radiation


  Radiation with a high enough energy to remove tightly bounded electrons from the orbit of an atom, causing the atom to become electronically charged.

  Eg: X-rays and Gamma rays
• Microwaves


  Can cause heating of internal body tissue, as microwaves are easily absorbed by water molecules and there is a lot of water in our bodies
• X rays are transmitted by soft / less dense tissue such as muscle and fat but they are absorbed by denser materials like bones
• Taking a picture of the body using X-rays allows us to see what the bones look like inside the body
• Short wave radio signals


  Are reflected by the earths ionosphere, therefore can travel long distances
• Long wave radio signals


  Are diffracted by obstacles such as hills, they follow the curvature of the earth, therefore can also travel long distances
• Radio waves in general are used for communications
• The higher the amplitude . . .


  The louder the sound of the wave.
• The higher the frequency . . .


  The higher the pitch of the wave
• State the equation linking Speed , Distance , Time

  Speed = Distance / Time