Physics Topic Twelve

• Waves transfer energy from one place to another without transferring matter. so we use them to transfer energy and information. the direction waves travel is the way they transfer energy. particles in a wave oscillate to and fro about a point, it is the whole wave that moves
• transverse waves for example a water wave are waves that oscillate perpendicular to the direction of the wave travelling
• longitudional waves for example a sound wave, the direction of the vibration of particles is parallel to the direction in which the wave travels. they are made of compressions and rarefactions
• mechanical waves travel through solids, liquids, and gases.
• electromagnetic waves are transverse waves that travel through a vacuum at the speed of light
• amplitude - the height of a wave crest or the depth of a trough measured from the midpoint of the wave
• the greater the amplitude the more energy it carries
• wavelength - the difference of one crest to the next
• the frequency of a wave is the number of wave crests passing a point in one second

  or in a longitudinal wave the number of compressions
• the period of a wave is the time it takes for one wave length to pass a point

  one/frequency
• the speed of a wave is the frequency x wavelength
• waves travelling towards a barrier are called incident rays
• reflection is at the same angle as the incident ray and there is no change in speed or wavelength
• waves can change speed when they cross a boundary between different surfaces. this is refraction
• sound is caused by mechanical vibrations in a substance and travels as a wave
• sound waves cannot transmit through a vacuum
• sound waves can be reflection from hard flat surfaces to produce echos
• Investigating waves:

  adjust frequency on oscillator until only a single loop on string

  note the frequency

  measure the length of the loop and calculate the wavelength - two x length

  calculate the speed of the wave

  change the frequency to obtain more loops

  calculate more values of speeds to see if the same or different