Sound and Ultrasound

1. they are caused by mechanical vibrations in a substance
2. vibrations are PARALLEL to the direction of travel

1. the ability to hear higher frequencies declines with age

Annotations:

• When calculating the distance of a reflecting surface from a person, remember that an echo goes there and back (divide by two) E.G. Sound travels at 340m/s. A person hears an echo 0.4 seconds after shouting - how far away is the reflecting surface? (340 x 0.4) = 136 136/2 = 68m

1. only hard, flat surfaces can reflect sound
   1. e.g. flat walls & floors
2. Soft objects/surfaces absorb sound
   1. e.g. carpets, curtains & furniture

1. the WAVELENGTH should be of the same order as the size of the obstacle or gap that diffracts the waves

1. determines the PITCH of a sound
   1. the higher the frequency the higher the pitch
2. = the number of vibrations each second
3. measured in Hertz (Hz)

1. determines the LOUDNESS (VOLUME) of a sound
   1. the greater the amplitude, the more energy the wave carries and the louder the sound
2. the 'height' of the wave

1. a device used to display the shape of an electrical wave
2. a short wavelength on the screen corresponds to a high frequency

1. waves with frequencies higher than 20,000Hz (20MHz)
2. non-ionising (safer than X-rays)
3. used for pre-natal scanning or to break down kidney stones so that they could be removed
4. Ultrasound scanners use a transducer to produce and detect ultrasound waves

   Annotations:

   • Again, the echoes are going there AND back, so the calculations will probably be halved again
   1. pulses of ultrasound are directed into the body
      1. they partially reflect from the tissue boundaries
         1. the reflected pulses are detected by the transducer

1. distance (between interfaces in various media) = wave speed x time taken