Waves and the Earth

Question 1

what is ultrasound

Answer 1

sound with frequencies greater than 20 000 hertz, Hz,

Question 2

what is infrasound

Answer 2

sound with frequencies less than 20 hertz, Hz,

Question 3

give a use of ultrasound regarding animals

Answer 3

1) Animals - can make and detect ultrasounds. the use these sounds to communicate with one another

Question 4

give a use of infrasound regarding animals

Answer 4

1) animals - whales and elephants use infra sound for communication. they can make infra sound and can also hear it.

Question 5

how are seismic waves generated

Answer 5

by earthquakes or explosions

Question 6

why do scientists find it difficult to predict earthquakes and tsunami waves even with available data

Answer 6

1) they don’t know how big the forces acting on the tectonic plates are
2) they don’t know the amount of friction on the plates or how strong they are so they cant predict when they will break

Question 7

give 2 possible features of seismic waves

Answer 7

can be longitudinal (P) waves and transverse (S) waves and that they can be reflected and refracted at boundaries between the crust, mantle and core

Question 8

give 2 types of seismic waves

Answer 8

can be longitudinal (P) waves and transverse (S) waves

Question 9

how is the Earth’s outermost layer is composed of (tectonic) plates and is in relative motion due to convection currents in the mantle

Answer 9

the outermost layer of the earth is divided into sections called tectonic plates. the plates move slowly, driven by convection currents in the earth’s mantle

Question 10

how do, at plate boundaries, plates slide past each other, sometimes causing earthquakes

Answer 10

tectonic plates move slowly driven by convection currents in mantle. no gaps between plates so their edges slide past each other. friction means they don’t slide smoothly. forces build up until part of the plate breaks. plates move with a sudden jerk.

Question 11

give a use of ultrasound regarding scans

Answer 11

2) Scans - make images of the inside of the body. to scan foetuses (unborn babies). ultrasound waves sent into woman`s body, some of the sound is reflected each time it meets layer of tissue with a different density to the one it has just passed through. scanner detects echoes and a computer uses information to make a picture.

Question 12

give a use of ultrasound regarding sonar

Answer 12

3) sonar - uses pulses of ultrasound to find the depth of water beneath a ship. sonar equipment measures the time between sending the sound and detecting its echo. this time is used to calculate the depth of the water.

Question 13

give a use of infrasound regarding detection of animals

Answer 13

special instruments detect sounds the animals make. allows scientists to follow the movements of animals. information about where animals are moving can help scientists to study them and recommend how animals can be protected

Question 14

give a use of infrasound regarding detection of meteors

Answer 14

meteors burn up as they travel through the earth’s atmosphere, as they pass through the air they produce infrasound waves, scientists can detect these waves, they work out how many meteors enter the atmosphere and the paths they follow

Question 15

give a use of infrasound regarding detection of volcanic eruptions

Answer 15

erupting volcanoes produce infrasound. infrasound is detected by instruments all over the earth. scientists detect volcanoes erupting in remote areas. scientists learn more about volcanoes and how they erupt. government can send help to people in the area.