Waves

• Waves may be either transverse or longitudinal.
• The ripples on a water surface are an example of a transverse wave.
• Longitudinal waves show areas of compression and rarefaction.
• Sound waves travelling through air are longitudinal.
• transverse waves have oscillations perpendicular to the direction of travel whereas longitudinal waves have oscillations parallel to the direction of travel
• The amplitude of a wave is the maximum displacement of a point on a wave
• The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.
• The frequency of a wave is the number of waves passing a point each second.
• The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
• Electromagnetic waves are transverse waves that transfer energy
• the EM waves are grouped in terms of their wavelength and their frequency
• the EM waves go from:

  • long to short wavelength
  • low to high frequency
• the EM waves (in order):

  • radio
  • micro
  • infrared
  • visible light
  • UV
  • xray
  • gamma
• 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 the process in which a wave changes speed and direction after entering a medium
• Radio waves can be produced by oscillations in electrical circuits.
• When radio waves are absorbed they create an alternating current with the same frequency
• Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed
• Gamma rays originate from changes in the nucleus of an atom
• waves that damage the human body tissue:

  • UV
  • X ray
  • gamma
• The effects depend on the type of radiation and the size of the dose
• UV can cause:

  • premature skin ageing
  • skin cancer
• X ray and Gamma are ionising radiation that can cause mutations in DNA and cause cancer
• radio waves are used for:

  • television
  • radio
• microwaves are used for:

  • satellite communications
  • cooking food
• infrared waves are used for:

  • electrical heaters
  • cooking food
  • infrared cameras
• visible light is used for fibre optic communications
• ultraviolet is used for:

  • energy efficient lamps
  • sun tanning
• X-rays and gamma rays are used for:

  • medical imaging
  • treatments.
• Radio waves are transmitted easily through air. They do not cause damage if absorbed by the human body
• • Microwaves have frequencies which are easily absorbed by molecules in food.
  • The internal energy of the food molecules increase when they absorb microwaves
  • which causes heating.
• Infrared light has frequencies which are absorbed by some chemical bonds. The internal energy of the bonds increases when they absorb infrared light