Waves

Waves

1. Sound Waves

   • Longitudinal waves - vibrating objects
     • travel to inner ear - eardrum - to hear it
   • Reflect & Refract
     • reflected by hard flat surfaces
       • rooms with carpet, furniture etc. absorb sound - stop echoes
         • delay between original sound & echo - echo has to travel further
   • Higher Frequency = Higher Pitch
     • frequency = complete vibrations each sec
     • Bigger Amplitude = Louder

2. Basics

   • Amplitude = rest position to crest
   • Wavelength = full cycle of wave
   • Frequency = no. of complete waves passing certain point per second (Hz)
   • Transverse = sideways vibrations
     • light & EM waves
     • ripples on water
     • Transverse Waves - waves = perpendicular to direction of energy transfer
     • waves on strings
     • slinky spring waved up and down
   • Longitudinal = same line vibrations
     • sound waves & ultrasound
     • shock waves
     • slinky spring pushed
     • Longitudinal = vibrations same direction as energy transfer
   • Speed = Frequency x Wavelength m/s = Hz x m

3. EM Waves & Uses

   • Microwaves - satellite communication & mobile phones
     • need microwaves that can pass through Earth's watery atmosphere - radio waves can't
       • signal transmitted into space - picked up by satellite orbiting - transmitted back to Earth - picked up by satellite dish
     • mobile calls - microwaves - to nearest transmitter
       • microwaves sometimes absorbed by water & heat them up - cells in body might cook - could damage health
   • Infrared Waves - remote controls & optical fibres
     • remotes - emit patterns of infrared to send commands
     • optical fibres e.g.phone lines - carry data quickly
       • use both infrared & visible light - signal carried as pulses of light/infrared & reflected off core from one end of fibre to other
   • Visible Light - photography
     • cameras use lens to focus visible light onto film/sensor
       • lens aperture - controls how much light enters camera
         • shutter speed - how long film/sensor exposed to light

4. Light

   • all waves reflect, refract, diffract
   • Reflection
     • light travelling in same direction reflects from uneven surface, reflects in different angles
     • light reflecting from even surface (smooth & shiny), reflected at same angle with clear reflection
     • Angle of INCIDENCE = Angle of REFLECTION
   • Diffraction
     • waves spread out - through gap/pass obstacle
       • narrower gap/longer wavelength = more the wave spreads
       • gap similar to wavelength = lots of diffraction e.g. sound through door
       • gap bigger than wavelength = little spreading e.g. light through door
   • Refraction - changing speed of a wave changes its direction
     • waves only refract if they meet new medium at an angle

5. EM Waves & Communication

   • Remember My Instructions Visible Under X-Ray Glasses
     • wavelength = 10ˉ¹⁵m to more than 10⁴m
     • travel at same speed in vacuum
     • higher frequency = shorter wavelength
   • Radio Waves = Communication
     • long-wave radio wavelengths can diffract around hills, into tunnels - receiver doen't need to be in line of sight of transmitter
     • short-wave radio signals (10m-100m) - can be received at long distances - reflect from ionosphere (electrically charged layer)
     • TV & FM radio = short wavelengths - have to be in direct sight

6. Origins of the Universe

   • Universe = Expanding
     • Galaxies light = red-shifted
       • chemical elements - absorb different frequencies
         • produce specific pattern of dark lines at frequencies it absorbs (on visible spectrum)
           • light from galaxies - same patterns at lower frequency - towards red end
     • Doppler Effect
       • Something moving towards you - frequency seems higher/wavelength seems shorter
       • Longitudinal & Transverse
     • Further Away Galaxy = Greater Red-Shift
       • all galaxies = moving away from us
         • more distant galaxies = moving away faster
   • Big Bang - 14 billion years ago
     • 'Steady State' theory - universe has always been/will be the same
       • cosmic microwave background radiation (CMBR) = leftover energy from Big Bang - strong evidence
         • low frequency electromagnetic radiation coming from all parts of universe
           • after Big Bang, universe was very hot - everything emitted high frequency radiation
             • as universe expanded, its cooled - now microwave radiation
   • Limitations
     • universe expansion should be slowing down but actually - speeding up
     • what caused explosion/conditions before