4.6.1.4 Sound Waves (physics only) (HT only)

Question 1

What can sound waves travel through?

Answer 1

• sound waves can travel through solids causing vibrations in the solid
• when sound waves move through the air, the air particles vibrate from side to side
• these vibrations can pass from one medium to another
• sound waves can only move through a medium e.g. air or a solid as the sound waves move by particles vibrating
• sound waves cannot pass through a vacuum as there are no particles

Question 2

What restricts the limits of human hearing?

Answer 2

• within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound
• this conversion of sound waves to vibration of solids works over a limited frequency range
• this restricts the limits of human hearing
• partly because of that, normal human hearing has a frequency range of 20Hz - 20,000Hz
• frequencies outside of that may not be able to cause the eardrum to vibrate

Question 3

How do humans hear sound?

Answer 3

• The outer ear (pinna) collects the sound waves and funnels them down the ear canal
• As it travels down, it still is a pressure air wave
• The sound waves hit the eardrum
  
  • Tightly stretched membrane which vibrates as the incoming pressure waves reach it
    
    • Compression forces the eardrum inward
    • Rarefaction forces the eardrum outward, due to pressure
  • The eardrum vibrates at the same frequency as the sound wave
  • The small bones (ossicles) connected to this also vibrate at the same frequency (stirrup bone)
  • The small bones act as an amplifier of the sound waves the eardrum receives
• Vibrations of the bones transmitted to the fluid in the inner ear
• Compression waves are thus transferred to the fluid (in the cochlea)
  
  • As the fluid moves due to the compression waves, the small hairs that line the cochlea move too
  • Each hair is sensitive to different sound frequencies, so some move more than others for certain frequencies
    
    • The hairs each come from a nerve cell
  • when a certain frequency is received, the hair attuned to that specific frequency moves a lot, releasing an electrical impulse along the auditory nerve to the brain, which interprets this to a sound

Question 4

How does sound travel from a source to your ear?

Answer 4

• sound waves travel from a source through oscillations of particles (parallel to the E transfer of the wave)
• object vibrates pushing air molecules into a series of compressions and rarefactions
• reaches the pinna which collects the sound waves into the ear

Question 5

Ear lobe/pinna:

Answer 5

collects the sound waves (acts as a funnel)

Question 6

Auditory canal:

Answer 6

wave travels along the canal

Question 7

Ossicles (3 small bones):

Answer 7

amplify the vibrations

Question 8

Cochlear:

Answer 8

turning vibrations into an electrical signal

Question 9

Auditory nerve:

Answer 9

carries the electrical signals to the brain

Question 10

What can the different parts of the eardrum do?

Answer 10

different parts of the eardrum can only vibrate at certain frequencies due to their size, shape and structure

Question 11

Auditory range:

Answer 11

the range of frequencies you can hear

Question 12

Auditory/hearing range of a human:

Answer 12

20Hz - 20,000Hz

Question 13

Why do humans auditory range decrease?

Answer 13

ossicles start to soften as age increases which means can’t amplify sound as much

Question 14

Can sound waves be reflected?

Answer 14

sound waves can be reflected - called an echo

Question 15

How do microphones work?

Answer 15

• when sound waves hit the paper cone (part of a microphone) it causes it to vibrate
• the microphone then converts this to electrical signals

Question 16

What happens when sound waves move from one medium to another?

Answer 16

• when waves move from one medium to another their speed can change
• sound waves travel much faster in solids than in gases as the particles in solids are much closer together —> this means that vibrations can pause more easily between them
• wave speed = frequency x wave length
  
  • when wave speed changes wave length also changes
  • frequency does not change when a wave changes medium
  • as the waves would have to be destroyed or created at the boundary which is not possible

Question 17

How can you view the features of sound waves?

Answer 17

• can view the features of sound waves by connecting a microphone to a cathode ray oscilloscope
• however, a cathode ray oscilloscope represents sound waves as transverse waves which is not correct as sound waves are longitudinal

Question 18

How do frequency and amplitude affect sound?

Answer 18

• high frequency sound has high pitch, low frequency sound has low pitch
• small amplitude small sound, large amplitude large sound

Question 19

Eardrum:

Answer 19

thin membrane

Question 20

What happens when a sound wave changes speed?

Answer 20

• whenever a sound wave changes speed some of the wave will be reflected
• the greater the change in speed, the greater the reflection

Question 21

What causes the sensation of sound?

Answer 21

within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound