Waves 2

Waves 2

1. Seismic waves

   • Seismology-study of earthquakes
     • Earthquakes measured using seismometers
   • Earthquakes occur when forces inside Earth increase+become strong enough to break and move layers of rock.Energy transferred making shock waves are called seismic waves. They occur in the Earth's crust(solid layer of rock 50km thick).
     • Seismic waves travel through the Earth. They're produced in an earthquake and spread out from the epicentre(first point on Earth's surface vertically from the surface)
       • Focus-Where an earthquake originates from
   • Primary seismic waves(P-waves)are longitudinal waves that compress+expand Earth's crust.
     • Secondary seismic waves(S-waves) are transverse and cause Earth's crust to oscillate up and down+side to side.Travel slower than P-waves.
       • Surface seismic waves(L-waves) arrive last in a seismic wave and only occur in the Earth's crust.They violently move materials backwards and forward.
       • • Surface waves are long waves
   • Evidence for Earth's cores
     • P-waves refract at boundary between mantle and outer core when the waves enter and leave the core as speed changes quickly at the boundary
     • S-waves are transverse so can't travel through liquid outer core as can't travel through liquid
     • Core has solid inner part that refracts P-waves at boundary between outer+inner core.
     • Discovered when it was found that the speed of seismic waves changed at depth of approx.50km below surface
   • 3 major layers of Earth
     • Mantle-Outer layer.P and S waves can travel through it
     • Outer core-Liquid.Only P waves can travel through as S waves can't travel through liquids
     • Inner core-Liquid.Only P waves can travel through as S waves can't reach it
   • Refraction-When a wave travels from 1 medium to another

2. Sound waves,The uses of ultrasound

   • no.of wavefronts=frequency
     • E.g.5 wavefronts=5Hz
   • Sound is the propagation(any which way a certain wave can travel)of longitudinal waves through matter.Sound waves travel through in all kinds of matter:solids,liquid and gas
   • An oscilloscope(CRO)allows you to see sound waves
     • Sound waves are converted to a visual representative of transverse waves as it's easier to see, record and present rather than as a visual representative as its actual form,a longitudinal wave
   • High amplitude sound waves would be sensed as a bright light and low amplitude a dim light
     • High amplitude sound waves are called 'loudness'
   • Our ears detect sound by converting vibrations in the airi.e. sound waves into mechanical vibrations in a solid
   • Audible range for humans
     • The conversion of sound waves to vibrations in bones only works over a limited range of frequencies.The human ear can detect sound over a range of 20hZ-20000Hz(20khZ)
   • Ultrasound waves are sound waves of frequency above 20kHz
   • Ultrasound waves are partly reflected at a boundary between 2 different types of body tissue.When they are reflected at boundaries they're timed and the timings are used to calculate distances
   • An ultrasound scan is non-ionising so it's safer than an X-ray.

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