Waves

Question 1

Compare water waves with sound waves

Answer 1

• Water waves are transverse, the oscillations move
  perpendicular (90 degrees) to the direction of energy transfer
• Sound waves are longitudinal, the oscillations move in the
  same direction as the direction of energy transfer. They
  require a medium to travel.

Question 2

Describe what a transverse wave and give examples

Answer 2

The oscillations move perpendicular (90 degrees) to the
direction of energy transfer e.g. water waves, EM
waves including visible light, S-waves released from
earthquakes

Question 3

Describe what a longitudinal wave is and give examples

Answer 3

The oscillations are in the same direction as the
direction of energy transfer. They require a medium to travel e.g. sound, ultrasound, infrasound, P-waves released from earthquakes

Question 4

How do we measure the wavelength of a soundwave by looking at particles

Answer 4

The distance from one compression to the next

Question 5

Recall the two equations for wave speed

Answer 5

• Wave Speed (m/s) = Frequency (Hz) x Wavelength (m)

- Speed (m/s) = Distance (m) / Time (s)

Question 6

Describe how light waves change when entering and leaving a glass block.

Answer 6

As light enters the glass block, it slows down and is refracted towards the normal. The wavelength decreases. When it leaves the block, it speeds up and is refracted away from the normal. The wavelength increases.

NOTE: sound waves do the exact opposite as they travel faster in solids, not slower.

Question 7

Describe how to calculate frequency

Answer 7

Frequency (Hz) = Number of waves / Time (s)

Question 8

Compare the appearance of high and low frequency waves

Answer 8

• High frequency: Shorter wavelengths, more waves, same
  amplitude
• Low frequency: Longer wavelengths, less waves, same
  amplitude

Question 9

Describe how we hear sounds starting from the ear canal

Answer 9

The eardrum vibrates due to sound waves. Vibrations are passed on to tiny bones which amplify the vibrations. The vibrations are passed onto the liquid inside the cochlea. Tiny hairs in the cochlea detect the vibrations and create electrical impulses. The impulses travel along neurons in the auditory nerve to the brain.

Question 10

Describe how the cochlea works

Answer 10

The cochlea is a coiled tube containing liquid. There is membrane of differing thickness in the tube. Different parts of the membrane vibrate depending on the frequency of sound waves in the liquid. Hairs along the membrane detect the vibrations and create electrical impulses which are sent to the brain to be interpreted.

Question 11

Define ultrasound and give examples of its use

Answer 11

Sound waves with frequencies above 20,000 Hz (upper range of human hearing) Used in sonar, ultrasound scans, echolocation in animals.

Question 12

Define infrasound and give an example of where it occurs

Answer 12

Sound waves with frequencies below 20 Hz (lower range of human hearing) Observed in seismic events (earthquakes)

Question 13

Explain how we use S and P waves to determine the structure of the Earth

Answer 13

• P waves: longitudinal waves. Can travel through liquids and
  solids.
• S waves: transverse waves. Can only travel through solids.

Seismometers around the world detect P and S waves and determine shadow zones where no waves are detected as below.