Waves

Waves

1. Waves

   • In a wave, a particle moves backwards/forwards or up/down, yet return to their starting points
     • This is an oscillation, however the wave itself moves forwards
   • Tranverse
     • Light, sea waves, seismic S waves, Mexican waves
     • The wave oscillates perpendicular to the direction of motion
       • Each part of the wave moves at right angles to the direction the energy is moving in
   • Longitudinal
     • Sound, seismic P waves, pressure waves
     • Each part of the wave moves in the same direction as the direction the energy is moving in
   • Parts of a wave..
     • Wave crest (top point of wave)
     • Wave length (difference between wave crests)
       • Measured in metres (m)
     • Wave trough (lowest point)
     • Amplitude (height from rest position)
       • Linked with volume
       • Measured in metres (m)
     • Frequency (number of oscillations/vibration per second
       • Linked with pitch
       • Units of Hertz

2. The spectrum

   • If a wave can travel through a substance we say the wave is transmitted through it
     • Substances can Transparent, translucent or opaque
   • All electromagnet waves travel at the speed of light in a vacuum, and are transverse waves
   • Each colour corresponds to a certain wavelength
     • Red the longest - Refracted the least in a prism
     • Violet the shortest - Refracted the most in a prism
     • Primary Colours (due to the way our eyes interpret light)
       • Red, green, blue
       • Filters absorb all colours they do not possess and transmit those they do
         • E.g. Yellow filters transmit only green and red light
       • Surfaces absorb all the colours they do not possess and reflect those that do
         • E.g. a red surface only reflects red light
     • Secondary colours (made of two primary colours
       • Magenta (B+R), Cyan (B+G), Yellow (G+R)
   • Infra red
     • Objects emit radiation due to their temperature
       • The higher the temperature the greater the amount of IR emitted
       • If an object gets hot enough it emits visible light (light bulbs)
     • Causes heating, exposure to small amounts warms a person
       • Exposure to large amounts causes burns
         • Firemen use protective clothing to protect themselves from this kind of wave
   • Ultraviolet light
     • can cause tanning
     • can cause materials to fluoresce
       • Meaning they shine with visible light
     • Three main categories of Ultra Violet radiation
       • UV - A
         • Longest wavelength
           • Causes tanning
       • UV - B
         • Medium wavelength
         • Damage cells
         • Causes sunburn and skin cancer
       • UV - C
         • Shortest wavelength
         • The most damaging
         • Filtered out by the Earths Ozone layer

3. Reflection and refraction

   • Reflection
     • All waves can be reflected
       • The ray hitting the mirror is the incident ray (it goes IN to the mirror)
         • The ray leaving the mirror is the Reflected ray
           • The angle of reflection is measured between the Normal and the reflected ray
         • the angle of incidence is measured between the Normal and the incident ray
     • Measure the angles formed from a line called The Normal
       • The Normal is an imaginary line that we draw at 90* to the mirror
   • Refraction
     • Sound and light waves change speed when they pass between the boundary of two substances with different densities
       • This causes them to change direction and this is called refraction
       • The more dense the substance the slower light moves through it