waves

• Waves


  Two types:
• Types of waves


  • Transverse
  • Longitudinal
• Transverse wave


  Wave for which the oscillations are perpendicular to the direction of energy transfer
• Longitudinal wave


  Wave for which the oscillations are parallel to the direction of energy transfer
• Transverse waves


  • Electromagnetic waves
  • Seismic s-waves
• Longitudinal waves


  • Sound waves
  • Seismic p-waves
• Parts of a longitudinal wave

  • Compressions
  • Rarefactions
• Wave amplitude


  Maximum displacement of a point on a wave from its undisturbed position
• Wavelength


  Distance from a point on a wave to the same position on the adjacent wave, most commonly peak to peak or trough to trough
• Wave frequency


  Number of waves that pass a given point each second
• Unit of frequency


  Hertz, Hz
• A frequency of 200Hz means 200 waves pass a given point each second
• Wave speed


  Speed at which the wave moves or at which energy is transferred through a medium
• Waves transfer energy
• Calculating wave speed


  1. Wave Speed = Frequency x Wavelength

  2. Speed (m/s), Frequency (Hz), Wavelength (m)
• Reflection


  When a wave bounces off a surface
• How sound waves travel through solids (Higher)

  The particles in the solid vibrate and transfer kinetic energy through the material
• Frequency range of human hearing (Higher)

  20 Hz - 20kHz (1kHz = 1000 Hz)
• Ultrasound waves (Higher)


  Waves which have a frequency higher than the upper limit of human hearing (20kHz)
• Uses of ultrasound waves (Higher)

  • Medical or industrial imaging
• Earthquakes cause seismic waves, which produce both P-waves and S-waves (Higher)
• Echo sounding technique (Higher)

  1. High frequency sound waves are emitted, reflected and detected

  2. Time difference between emission and detection, alongside wave speed, are used to calculate distances
• Electromagnetic spectrum


  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