Physics Chpt 12

• What's a wave?


  a wave is a transfer of ernegy from one point to another
• what are the 2 main types of waves?

  Mechanical= vibrate through a medium(substance) and Electromagnetic= travel through a vacuum(no medium needed)
• Transverse waves


  oscillations are perpendicular to the direction of energy transfer
• Longitudinal waves


  Oscillations are parallel to the direction of energy transfer
• frequency


  how many waves pass a point per second
• wave speed=

  v=

  Wave speed (m/s) = frequency (Hz) x wave length (m)

  V= F x λ
• Time period =

  T=

  Time period (seconds)= 1/frequency(Hz)

  T=1/f
• wavelength of a wave=


  distance from a point on the wave to the equivalent point on the adjacent wave
• speed=


  speed=distance/time
• At a boundary between 2 materials light can be:


  • Reflected
  • Transmitted (refracted)
  • Absorbed
• Sound waves are vibrations that travel through a medium
• Sound and waves


  the higher the pitch, the higher the frequency
• Ultrasound waves are used for 


  • pre-natal scanning
  • cleaning jewellery
  • medical uses
• Advantages of ultrasounds


  • non-ionising
  • partly refelcets off boundaries between types of tissue (due to change in density/material)
  • used in medicine
• Disadvantages of x-rays


  • ionising radiation (can lead to mutations/cancer)
  • not reflected at boundaries between different tissues
• Sound needs particles to travel. Sound can travel through liquids and solids.
• when sound redlects of a surface it's called an echo
• Seismic waves


  gerneated by earthquakes
• Where are seismic waves produced?

  produced in an earthquake. They spread out from the epicentre
• Epicentre=?

  Nearest point on the surface to where the earthquake originates
• What 2 waves do earthquakes cause?

  • P-Waves (longitudinal)
  • S-Waves (transverse)
• P-waves can travel through the liquid outer core but are refracted creating a zone where the waves don't reach
• what happens when p-waves reach a boundary

  they are refracted, so they change speed causing them to change direction. This creates a shadow zone where they are ubable to reach from the focus
• S-waves are unable to travel through the liquid outer core
• P-waves can travel theough both the mantle and the outer core

  S-waves can only pass through the crust and mantle