Ultrasound and infrasound

Question 1

ultrasound

Answer 1

sound waves with a frequency above 20kHz

Question 2

infrasound

Answer 2

sound waves with a frequency below 20Hz

Question 3

What is infrasound produced by?

Answer 3

shockwaves from tsunami, volcanoes or earthquakes

explosions under the ground

produced when meteors enter the Earth’s atmosphere

Question 4

How can infrasound be used?

Answer 4

scientists can track the path of a meteor using the infrasound it produces

infrasound waves are detected from explosions under the ground, which can help to determine the structure of rocks beneath the earth’s crust

seismic P waves are infrasound, so can be used to determine the structure of the Earth

Question 5

uses of ultrasound waves

Answer 5

pre-natal scans
waves are used to make images of the inside of the body
waves aren’t harmful, so can be used on foetuses

breaking kidney stones

cleaning jewellery

detecting cracks in machinery

Question 6

pre-natal scans and ultrasound

Answer 6

• ultrasound waves are sent into the women’s body
• some of the sound is reflected each time it meets a layer of tissue with a different density
• a scanner detects the echos and a computer uses the information to make a picture

Question 7

breaking kidney stones, cleaning jewellery and ultrasound

Answer 7

vibrations caused by ultrasound shake apart the dirt or kidney stones, breaking them up

Question 8

What happens when ultrasound meets a boundary between two different materials?

Answer 8

• some of the ultrasound is reflected at the boundary
• the time taken for waves to leave a source and return to a detector is measured
• the depth of the boundary can be determined using the speed of sound in the material and the time taken

Question 9

sonar/echo sounding and ultrasound

Answer 9

sonar uses pulses of ultrasound to find the depth of water beneath a ship
the sound waves used are (sometimes) within normal hearing range

(bats use echolocation in the same way)

it could also be used to detect submarines or animals in the water

sonar equipment measures the time between sending the sound and detecting its echo

this time is used to calculate the depth of the water: distance = speed x time

(the depth is half the distance travelled)

Question 10

A ship detects an echo 5 seconds after it has sent out a sonar pulse.

Sound travels at 1500m/s in sea water. How deep is the water?

Answer 10

d = st
= 1500 x 5
= 7500 m

depth of water: 7500/2 = 3750 m

Question 11

Describe the similarities and differences between sound, infrasound, and ultrasound. [3]

Answer 11

all longitudinal waves

infrasound has lower frequencies/longer wavelengths than normal sound

ultrasound has higher frequencies/shorter wavelengths than normal sound

Question 12

Describe how ultrasound waves can be used to produce an image of a foetus [4]

Answer 12

ultrasound waves are sent into the body from a transmitter

ultrasound waves are reflected at a boundary between materials of different density

the reflected ultrasound is then detected by the receiver

an image is produced on a computer monitor based on information from the reflected ultrasound

Question 13

A sonar signal is sent from a ship. The echo is received 0.2s later, back at the ship. The sound wave has travelled a total distance of 284m.

Calculate the speed of sound in water. [3]

Answer 13

s = d/t = 284/2 = 1420 m/s