P1 Topic 4 - Waves And The Earth Flashcards
Where is ultrasound used?
Pre-natal scanning:
Ultrasound passes through the body, but when it crosses through a different medium, some is reflected back and detected by the scanner.
The time and distribution are recorded by a computer and analysed to produce an image of the foetus.
Sonar:
Boats and submarines emit ultrasound which reflects of objects in the water around them, the reflected waves are picked up by detectors and used to produce an image and work out how far away these objects are.
What is ultrasound?
It is sound with frequencies higher than 20,000 Hz.
What is infrasound?
Infrasound is sound with frequencies lower than 20Hz.
Where can you find infrasound?
It travels over long distances and diffracts around objects easily.
Therefore, elephants and tigers use infrasound to communicate over long distances.
How do you calculate distances using ultrasound?
Distance (m) = (Wave Speed (m/s) x Time (s)) / 2
What are the two waves released in an earthquake?
Explain their differences.
P-waves and S-waves
P-waves: longitudinal, travel through solids and liquids, faster than S-waves
S-waves: transverse, only travel through solids, slower than P-waves
How are seismographs used to pinpoint the location of earthquakes?
P-waves and S -waves travel at different speeds and therefore arrive to you at different times. Using the time difference of the two waves, the distance from you to the epicentre of the earthquake can be worked out. Then, by drawing a circle around your location with the radius of the distance, you have a distance arc. By drawing two more distance arcs using distances from two other seismometers, you can locate the epicentre of the earthquake from the point at which they all cross over.
