6. Waves

• Transverse

  Vibrations are at a right angle to the direction of the energy transfer. The wave has crests and troughs.

  E.G water and light waves
• Longitudinal

  The vibrations are in the same direction (parallel) as the energy transfer. The was has areas of compression and rarefaction.

  E.G sound and seismic waves
• The frequency of a wave is the number of waves which pass a given point every second
• To measure the speed of sound use the equation

  speed = distance*time

  Remember the distance will be double because the wave has travelled to the wall and back again.
• How quickly waves can travel through a medium is determined by the density of the medium.
• Sound waves will travel faster through a solid quicker than a liquid as the spaces between the particles are smaller. This means the vibrations and energy can be passes along the particles quickly.
• specular reflection occurs when a wave is reflected in a single direction from a perfectly smooth surface
• angle of incidence = angle of reflection
• Diffuse reflection occurs when a wave is reflected in many directions and happens at a rough or uneven surface
• Refraction occurs when a wave changes speed, usually at the boundary or two different materials. The density of the material affects the speed at which the wave can travel through it.
• When a wave passes from a more dense material to a less dense material it speeds up and so will bend
• A sound wave can travel through a solid material. This is because the space between the particles is so small and the vibrations are transmitted so quickly than in liquid or gases
• Sound waves don't travel in space
• Sound waves within the range 20Hz to 20kHz can usually be detected by the human ear
• Vibrations are passed along air down in the ear canal and to the ear drum. The ear drum vibrates and transmits this to the small bones and then along the cochlea. The cochlea carries the vibrations to the auditory nerve which carries the sound to the brain.
• A shorter wavelength results in a high-pitched sound
• A greater height of oscillations indicates a higher volume of the wave
• Ultrasound is used for medical and industrial imaging
• Sonar systems used to explore deep seas use high-frequency sound waves to detect objects and map the seafloor.
• Volcanoes, earthquakes cause seismic waves to travel through the earth.
• P-Waves are longitudinal which travel quickly through solids and liquids
• S-Waves are transverse waves and they are slower and only in solids
• Seismic waves can change direction when they are reflected or refracted at the boundary of different media.
• The epicentre of an earthquake can be found by calculating the difference in time taken for S- and P-waves to reach a certain point
• The study of seismic waves have given scientists new evidence about the structure of the earth in parts which are not visible for direct observations.