Waves

• Longitudinal wave


  Particles move back and forth in the same direction as the wave is travelling
• Transverse wave


  Particles move up and down at right angles to the direction the wave is moving
• Sea waves transfer energy to the shore. When waves hit the land, the energy is transferred to the land and can wear it away
• Waves on the surface of water are transverse waves. Particles in the water move up and down as a wave passes-the particles are not carried to the shore
• Sound waves are longitudinal waves. Particles in the material through which the wave is travelling move backwards and forwards as the wave passes
• Earthquakes and explosions produce seismic waves that travel through the Earth. Solid rock material can be pushed and pulled (longitudinal seismic waves) or moved up and down, or side to side (transverse seismic waves)
• Electromagnetic waves (such as light, radio waves, microwaves) are transverse waves and do not need a medium (material) through which to travel
• Wave frequency


  The number of waves passing a point each second, measured in hertz (Hz)
• Period


  The length of time it takes one wave to pass a given point
• Wavelength


  The distance from a point on one wave to a point in the same position on the next wave, measured in metres
• Amplitude


  The maximum distance of a point on the wave away from its rest position, measured in metres
• Wave velocity


  The speed of the wave in the direction it is travelling
• Changes in the frequency, wavelength or amplitude of a wave can be used to transfer information from one place to another. For example, when you listen to FM radio, the music is sent by variations in the frequency of the radio waves
• Measuring the speed of waves

  1. Measure the time it takes for a sound to travel a certain distance

  2. Measure the time it takes for a wave to travel between two fixed points on water
• Wave speed

  Linked to wave frequency and wavelength by the equation: wave speed (m/s) = frequency (Hz) x wavelength (m)
• Light always travels at 300 000 000 m/s in a vacuum but it travels more slowly in glass or water. When light goes from air into water its wavelength also reduces
• The speed of a wave depends on the medium through which it is travelling
• Most waves travel outwards from their source in straight lines. However, waves can change direction when they move into a different medium. The change in direction is called refraction and happens at the interface (boundary) between the two media
• Light travelling along the normal does not change direction when it goes into a different medium
• An object on the bottom of a swimming pool looks closer than it really is because light reflected by it changes direction when it leaves the water
• As light passes the interface between one medium and another it changes speed. This change in speed causes the direction of the light to change
• The bend depends on how fast the light travels in the two media and the angle of the light hitting the interface. The greater the difference in speed between the two media, the more the light is bent. The light bends towards the normal when it slows down
• The speed of waves on water depends on how deep the water is. Waves moving from deep water into shallow water slow down and change direction