Wave properties

12.1 The nature of waves

• Waves transfer energy w/out transferring matter
• Mechanical waves are virbations that travel through a medium (a substance). They can be transverse or longitudinal. Examples:
  • Sound waves
  • Water waves
  • Waves on springs and ropes
  • Seismic waves from earthquakes
• Electromagnetic waves can travel through a vacuum at 300,000 km/s. (Doesn't need a medium). Examples are:
  • Light waves
  • Radio waves
  • Microwaves
• To observe a wave travelling through a substance:
  • look at waves spreading out on water after a small object's dropped in the water. The waves travel across the water, the water doesn't travel away from the object
  • tuning forks vibrate to make sound waves. The air doesn't travel away from the object
• Transverse waves oscillate perpendicular to the direction in which the waves are moving. Waves on a rope are transverse because the vibrations move up and down or from side to side. Electromagnetic waves are transverse.
• Longitudinal waves are parallel to the direction in which the waves transfer energy. Sound waves are longitudinal. When objects vibrate in air, the air around it vibrates as it pushes and pulls on the air.

12.2 The properties of waves

• Amplitude is the maximum displacement of a point on the wave from its undisturbed position. The bigger the amplitude of the waves, the more energy the waves carry
• The wavelength of a wave is the distance from a point on the wave to an equivalent point on the next wave. 
• The no. of waves passing a fixed point every second is called the frequency
• period, T (s) = 1/frequency, f (Hz)
• The speed of the waves is the distance travelled by each wave every second through the medium. Energy's transferred by the waves at this speed
• wave speed (m/s) = frequency (Hz) x wavelength (m)
• To measure the speed of air crash 2 symbols together and time how long it takes for a person, a set distance away, to hear the bang, then use speed = distance/time

12.3 Reflection and refraction 

• Reflection can be measured using a ripple tank. Use a ruler to make direct plane waves at a straight barrier. Find out if the reflected waves are always at the same angle to the barrier as the incident waves. Align a second ruler w/ the reflected waves and measure the angle of each ruler to the barrier. Repeat at various angles.
• Incident waves are relfected by the barrier 
• Refraction of waves is the change of direction in which they're travelling along when they cross a boundary between 1 medium and another. This is seen in a ripple tank when water waves cross a boundary between deep and shallow water. Use a vibrating beam to make plane waves in a ripple tank containing a clear plastic plate. Arrange plate so waves cross a boundary between deep and shallow water. At a non -0 angle the waves change their speed and direction when they cross a boundary. See if plane waves change direction towards or away from the boundary when they…