Waves

Waves

1. The nature of waves

   • we use waves to transfer energy and to transfer information
   • transverse waves vibrate at right angles to the direction of energy transfer. All electromagnetic waves are transverse waves.
   • longitudinal waves vibrate parallel to the direction of energy transfer. A sound wave is longitudinal
   • mechanical waves, which need a medium (substance) to travel through, may be transverse or mechanical waves

2. Measuring waves

   • for any wave, the amplitude is the height of the wave crest or the depth of the wave trough
   • for any wave, the frequency is the number of wave crests passing a point in a second.
   • for any wave, the wavelength is the distance from one wave crest to the next wave crest

3. Wave properties: reflection

   • the normal at a point on a surface is a line drawn perpendicular to the surface
   • angles are always measured between the light ray and the normal
   • the law of reflection states that: the angle of incidence is equal to the angle of reflection

4. Wave properties: refraction

   • refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances
   • if the speed is reduced, refraction is towards the normal (e.g air to glass)
   • if the speed is increased, refraction is away from the normal

5. Wave properties: diffraction

   • diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle
   • the narrower a gap, the greater the diffraction
   • if radio waves do not refract enough when they go over hills, reception will be poor

6. Sound

   • the frequency range of the normal human ear is from 20Hz to 20kHz
   • sound waves need a medium in which to travel
   • reflections of sound are called echoes

7. Musical sounds

   • the pitch of a note increases if the frequency of the sound waves increase
   • the loudness of a note depends on the amplitude of the sound waves
   • vibrations created in an instrumental when it is played produce sound waves