P12.5-7 Flashcards
why is human hearing limited
Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range. This restricts the limits of human hearing.
echo sounding
ultrasound for medical images
adv. of ultrasound for medical scanning (vs X-rays)
interpreting oscilloscopes
2 IMPORTANT facts abt sound waves
longitudinal (SO TRAVEL FASTER IN DENSER MEDIUMS)
require particles to propagate (cant travel in vacuums)
P-waves vs S-waves
push and pull rock particles vs side to side moving rock particles
l vs t
both through solids, only p-waves through liquids
p waves faster
p waves do less damage
shadow zone - why?
When an earthquake happens, seismometer readings from different parts
of the world are used to find out where its epicentre is.
P-waves and S-waves bend as they travel through the mantle. This
is because their speed changes gradually with depth, and so their
direction changes with depth.
P-waves refract at the boundary between the mantle and the outer
core. This is because their speed changes abruptly at the boundary.
S-waves are transverse waves, and so they can’t travel through the
liquid outer core.
When an earthquake happens, some seismometers record only long
waves. These seismometers are in the shadow zone of the earthquake
(Figure 3), which is a zone from about 105° to 142° where no P-waves or
S-waves are recorded.
what can we learn about earths structure from seismic waves
seismic waves’ paths curve- gradual change in density of mantle
S-Waves not detected on opposite side of the earth - outer core must be liquid
kinks in paths of P-waves travelling to the other side of the Earth suggest a sudden change in density of the material
existence of shadow zons where P-waves are not detected suggest a solid inner core.
PQ: why is speed of seismic waves faster in mantle than in crust
One reason for the higher speed of seismic waves in the mantle is that the mantle is denser than the crust, which leads to faster transmission of seismic waves.
Another reason could be in the higher temperatures and pressures in the mantle compared to the crust. Higher temperatures in the mantle cause the rock to have higher elasticity, allowing seismic waves to propagate more quickly.
EQ: explain how we can see diff. parts of foetus in an ultrasound scan (4)
Different parts of the fetus are visible in an ultrasound scan because ultrasound waves travel at different speeds through various tissues.
When ultrasound waves encounter boundaries between tissues with different densities and speeds, some waves are reflected back while others continue traveling.
Example: Ultrasound waves move more slowly in amniotic fluid (1540 m/s) than in bone (3080 m/s), causing strong reflections at the boundary, making bones clearly visible.
Differences in velocity between muscle (1585 m/s), liver (1549 m/s), and kidney (1561 m/s) cause partial reflections, helping to distinguish these structures.
The ultrasound machine processes these reflected waves to create an image of the fetus.
