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sound

1. properties

   • longitudinal waves
     • vibrate in the same direction as the direction of travel
   • produced by vibrating sources
     • speakers
   • only travel through a solid, liquid or gas medium
     • fasted in solids - then liquid - slowest in gases

2. sections of the sound waves where the particles are pushed together are ares of compression.

3. sections of the sound waves where the particles are further apart are areas of rarefaction

4. ultrasound

   • name given to sound waves that have frequencies greater than 20,000 Hz

5. oscilloscopes and sound

   • machine that shows the wave shape of an electrical signal
   • when connected to a microphone they can show the wave shapes of sounds
   • frequency = 1 / time period

6. analogue and digital signals

   • analogue signals
   • dialogue signals
     • series of pulses consisting of two states
       • on - 1
       • off - 0

7. data transmission

   • digital signals maintain their quality better than analogue signal
   • noise
     • all signals become weaker as they travel long distances
     • may also pick up random extra signals
       • called noise
     • it is heard as crackles and hiss on radio programs
   • analogue signals
     • noise adds extra random information
       • each time signal is amplified- noise is also amplified.
         • gradually signal becomes less and less like the original signal.
   • digital signals
     • noise is usually lower in amplitude than the amplitude of the ON states.
     • quality of the signal is maintained
     • because digital signals can carry more info per second than analogue signals, higher quality programs or more channels can be broadcast.
     • information can be stored and processed by computers.

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