Wave Properties Notes

12/1/14   The  Nature  of  Waves   Unit  6   Waves  Only  Carry  Energy   — What’s  in  a  Wave?   — A  wave  is  a  repeating  disturbance  or  movement  that   transfers  energy  through  matter  or  space   — Waves  and  Energy   — The  molecules  of  the  substance  transfer  some  of  the   energy  to  neighboring  molecules  causing  them  to  move   (think  Dominoes)   — Waves  only  carry  energy,  they  do  not  transport  matter   (PICTURE)   — All  waves  are  produced  by  a  disturbance  or  vibrations   (NEXT)   The  Nature  of  Waves,  con$nued   BACK   The  Nature  of  Waves,  con$nued   Two  Types  of  Waves:     1. Mechanical  Waves   — Require  a  medium    -­‐    A  medium  is  the  matter  through  which  waves   travel    -­‐    May  be  solid,  liquid  or  gas     — Ex:  Water  waves,  sound  waves     2. Electromagnetic  Waves   — Do  not  require  a  medium   — Ex:  Light  waves   Transverse  Wave   — Mechanical  Waves   — There  are  two  types  of  mechanical  waves:   — Transverse  waves   — — — Compressional  waves   — — — Matter  moves  back  and  forth  at  right  angles   (perpendicular)  to  the  direction  of  the  wave  (PICTURE)   Example:  water  waves   Matter  moves  in  the  same  direction  (parallel)  as  the   direction  of  the  wave  (PICTURE)   Example:  sound  waves   Some  waves  are  a  combination  of  transverse  and   compressional  (PICTURE)   — Example:  ocean  waves  and  seismic  waves     BACK   1   12/1/14   Compressional  Wave   Combina?on  (Surface)  Waves   BACK   Warm-­‐up   1. 2. 3. 4. 5. 6. BACK   Wave  Proper?es   Waves  carry  __________  through  matter  or  space.     True  or  False:  Waves  are  caused  by  a  disturbance.     A  wave  that  requires  a  medium  is  called  a  ________  wave.     The  only  type  of  wave  that  does  not  require  a  medium  is  a   ____________  wave.     Light  is  an  example  of  a  (transverse  /compressional)  wave.     Sound  is  an  example  of  a  (transverse  /compressional)  wave.   Different  Looks   — The  Parts  of  a  Wave   — Waves  differ  in  the  following  ways:   — — — How  much  energy  they  carry   How  fast  they  travel   How  they  look   — Transverse  waves  have  high  points  and  low  points   — Highest  point  =  crest   — Lowest  point  =  trough   — Compressional  waves  have  regions  of  high  and  low  density   — High  density  (squished)  regions  =  compressions   — Low  density  (stretched)  regions  =  rarefactions  (PICTURE)   (NEXT)   Wave  Proper?es,  con$nued   — Wavelength   — The  wavelength  is  the  distance  from  one  point  on  a   wave  and  the  nearest  point  just  like  it   BACK   2   12/1/14   Wave  Proper?es,  con$nued   Wavelength  and  Frequency   Rela?onship   — Frequency   — The  number  of  wavelengths  that  pass  a  fixed  point  each   second   — Measures  in  hertz  (Hz  or  1/s)   — As  the  frequency  increases,  wavelength  decreases  (PICTURE)   — Frequency  is  always  equal  to  the  rate  of  vibrations  of  the   sources  that  creates  it   — — If  you  move  a  rope  up-­‐and-­‐down  once,  the  frequency  is  1  Hz   If  you  move  a  rope  up-­‐and-­‐down  fives  times,  the  frequency  is  5  Hz   — The  opposite  of  frequency  is  period     — The  time  that  it  takes  a  complete  cycle  or  wave  oscillation  to  occur          (NEXT)   1   1   T  =  1/f   frequency = or f = period BACK   T Wave  Proper?es,  con$nued   Amplitude  of  Compressional  Waves   — Amplitude   — A  measure  of  the  energy  in  a  wave   — — — — The  greater  the  energy  the  wave  carries,  the  greater  its   amplitude   The  amplitude  of  compressional  waves  is  related  to  how   tightly  the  medium  is  pushed  together   — The  denser  the  compressions,  the  larger  the  amplitude  (and   energy)   — The  less  dense  the  rarefactions,  the  larger  the  amplitude  (and   energy)  (PICTURE)   The  amplitude  of  transverse  waves  is  the  distance  from  the   crest  or  trough  to  the  normal  position  of  the  medium   (PICTURE)   Examples:  how  high  an  ocean  wave  appears  above  the  water   level  (NEXT)   Amplitude  of  Transverse  Waves   BACK   Typical  Wave   A. How  many  wavelengths  are  there?   B. What  is  the  frequency  of  this  wave?   C. What  is  the  period  of  this  wave?   1  second   BACK   3   12/1/14   Warm-­‐Up   1. 2. 3. 4. 5. Time  required  for  one  wave-­‐ length  to  pass  a  given  point   Greatest  distance  particles  are   displaced  from  resting  position   Highest  point  of  a  transverse   wave   Distance  from  one  crest  to  the   next  or  one  compression  to  the   next   Relationship  between  period  and   frequency   Wave  Proper?es,  con$nued   A. Wavelength   B. f  =  1/T   C. Crest   D. Amplitude   E. Period   — Wave  Speed   — Wave  speed  equals  frequency  times  wavelength     speed = distance time v= d t speed = wavelength period speed = frequency × wavelength v = Tλ v = f ×λ — Light  waves  travel  faster  than  sound  waves   — Sound  waves  travel  faster  in  liquids  and  solids  than  in  gases   — Light  travels  faster  in  gases  and  empty  space  than  in  liquids   and  solids   (FURTHER  EXPLANATION)        or  (EXAMPLE  PROBLEMS)   EXTRA   INFORMATION!   Use  only  if  further   explanation  needed   Wave  Proper?es,  con$nued   — Wave  Speed   — The  speed  of  a  wave  depends  on  the  medium.   — The  arrangement  of  particles  (kinetic  theory)  in  a  medium   determines  how  well  waves  travel  through  it   — — — In  gases,  the  molecules  are  far  apart  and  move  around   randomly  (PICTURE)   — Thus,  waves  don’t  travel  as  fast  in  gases   In  liquids,  such  as  water,  the  molecules  are  much  closer   together  (PICTURE)   — But  they  are  also  free  to  slide  past  one  another   In  a  solid,  molecules  are  not  only  closer  together  but  also   tightly  bound  to  each  other  (PICTURE)   — Waves  travel  very  quickly  through  most  solids   4