Waves (Extended Response)

Question 1

Waves transfer energy without there being any overall transfer of matter.

These waves can be two different types.

Explain how the wave motion that occurs is related to the disturbance that is causing it and the material it is moving in.

Your answer should refer to real-life examples of both types of waves.

Answer 1

a longitudinal wave is produced when the vibration is parallel to the direction of energy transfer

a transverse wave is produced when the vibration or oscillation is at right angles to the direction of energy transfer

sound waves, infrasound and ultrasound waves are all longitudinal waves, as well as seismic P waves

these waves can only transfer energy is there is a medium (solid, liquid or gas) for them to travel through

some transverse waves also travel through matter, including water waves and seismic S waves (which is why they cannot travel through liquid)

unlike longitudinal waves, some transverse waves can travel through a vacuum and do not need a medium
this is the case for all electromagnetic waves (e.g. ultraviolet waves)

Question 2

The human ear can detect sound between 20Hz and 20kHz. Describe uses of the frequencies of sound waves that cannot be detected by the human ear.

Answer 2

• sound frequencies below 20Hz are called infrasound
• above 20kHz are called ultrasound

-infrasound can be used to explore the earth’s core and to detect volcanic eruptions

• ultrasound is used for medical imaging (e.g. pre-natal scans)
• ultrasound can be used for distance measuring in sonar equipment (depth of sea bed, shipwrecks, shoals of fish)
• ultrasound is used for detecting cracks in pipes or machinery