What is the human hearing range?
20Hz - 20,000Hz
What are ultrasound waves?
Sound waves about the human hearing range (20,000Hz).
What are some uses of ultrasound?
- Pre-natal scans
- Breaking down kidney stones
- Echolocation (finding cracks, etc.)
How do ultrasound scans work?
- TRANSDUCER sends out ultrasound waves.
- The waves are partially REFLECTED at each BOUNDARY between MEDIUMS.
- The TRANSDUCER detects the returning waves.
- Since ultrasound waves travel at VARIOUS SPEEDS in different mediums, the connected computer can process the sequence of returning waves and calculate the distances to the boundaries.
- From this, an IMAGE is formed on the screen.
What are the advantages of ultrasound waves over X-Rays?
- Non-ionising and therefore harmless.
* Reflected at boundaries so they can be used to scan soft tissue.
How is distance travelled by an ultrasound wave calculated?
Distance travelled = Speed of ultrasound in medium x Transit time
(Distance = Speed x Time)
Half of the distance travelled is the distance to the boundary.
Define amplitude.
The height of the wave, either from node to crest or from node to trough.
Define wavelength.
The distance between two corresponding points on a wave. (E.g. From crest to crest)
Define crest.
The highest point of a wave from the node.
Define trough.
The lowest point on a wave from the node.
How does sound travel through air?
Vibrating air particles cause air particles near them to vibrate. A vibrating object ‘pushes’ and ‘pulls’ the air, creating compressions and rarefactions.
Are sound waves longitudinal or transverse?
Longitudinal
What is an echo?
A reflection of sound off a surface.
What is the difference between musical notes and noise?
- Musical notes are easy to listen to because they are rhythmic. The sound waves change smoothly and the pattern repeats.
- Noise consists of sound waves that vary without pattern.
What does an increase in amplitude mean?
The sound gets louder.
How is an increase in amplitude shown on an oscilloscope?
The waves become taller.
What does an increase in frequency mean?
The pitch of the sound increases.
How is an increase in frequency shown on an oscilloscope?
More waves appear (i.e. They become narrower)
What is meant by an instrument resonating?
It produces recognisable notes at specific frequencies.
