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 a longitudinal wave
   • Mechanical waves, which need a medium (substance)to travel through, may be transverse or longitundinal

2. Measuring Waves

   • For any wave, its amplitude is the height of the wave crest or the depth of the wave trough, from the position at rest
   • For any wave, its frequency is the number of wave crests passing a point in one second
   • For any wave, its wavelength is the distance from one wave crest to the next wave crest. This is the same as the distance from one wave trough to the next wave trough

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 (e.g. glass into air)

5. Wave Properties: Diffraction

   • Diffraction is 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 diffract enough when they go over hills radio and TV reception will be poor

6. Sound

   • The frequency range of the normal human ear is from about 20 Hz to about 20kHz
   • Sound waves are longitudinal
   • Sound waves need a medium in which to travel
   • Echoes are reflections of sound

7. Musical Sound

   • The pitch of a note increases if the frequency of the sound waves increases
   • The loudness of a note depends on the amplitude of the sound waves
   • Vibrations created in an instrument when it is played produce sound waves

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