6.2 Electromagnetic Waves

• Electromagnetic spectrum


  A continuous spectrum
• Types of electromagnetic radiation ordered from lowest to highest frequency

  • Radio waves
  • Microwaves
  • Infrared
  • Visible Light
  • Ultraviolet
  • X-rays
  • Gamma Rays
• Electromagnetic waves all travel at the same speed in a vacuum and in air
• Refraction


  Caused by the difference in wave speed in different mediums
• When waves enter a denser medium, they bend towards the normal and the angle of refraction is less than the angle of incidence
• Radio waves


  Can be produced by oscillations in an electrical circuit
• How radio waves create an alternating current in a circuit

  Radio waves are absorbed, inducing oscillations in the circuit with the same frequency as the waves
• Gamma rays


  Originate from changes in the nuclei of atoms
• Ultraviolet waves


  • Can cause the skin to age prematurely
  • Can increase the risk of developing skin cancer
• 1. rays and Gamma rays

  • Are ionising radiation so can cause mutations in genes
  • Can lead to increased risk of developing various cancers
• Practical uses of infrared radiation

  • Electrical heaters
  • Cooking food
  • Infrared cameras
• Practical uses of microwave radiation

  • Satellite communications
  • Cooking food
• Practical uses of radio waves

  • Television transmission
  • Radio transmission
• Refraction


  The wave phenomenon used by lenses to form an image
• How a convex lens forms an image


  Parallel rays of light are refracted and brought together at a point known as the principal focus
• Focal length of a lens


  The distance from the lens to the principal focus
• Difference between images produced by convex and concave lenses

  • Convex lenses can produce real or virtual images
  • Concave lenses can only produce virtual images
• Magnification does not have a unit
• Magnification


  The ratio between image height and object height, which does not require units
• The symbol used to represent a convex lens in a ray diagram is
• The symbol used to represent a concave lens in a ray diagram is
• Colour of visible light


  Determined by the wavelength and frequency of the light waves
• The colour of visible light with the highest frequency is
• The colour of visible light with the largest wavelength is
• Specular reflection


  Reflection from a smooth surface in a single direction
• Diffuse reflection


  Reflection from a rough surface which causes scattering
• How a red colour filter works

  Absorbs all wavelengths of light other than those in the red range of the spectrum, allowing only red light to pass through
• Colour of an opaque object


  Determined by the wavelengths of light that are most strongly reflected by the object
• The wavelengths of light that aren't reflected by an opaque object are absorbed by the object
• If all wavelengths are reflected by equal amounts, the object appears
• If all wavelengths are absorbed, the object appears