P3.4 sound wave

Question 1

Overview of sound wave

Answer 1

• Mechanical wave, requires a medium to transmit sound waves and it is a longitudinal wave
• Produced by a vibrating source
• Travel faster in more dense material

Question 2

The approximate range of frequencies audible to humans

Answer 2

20 Hz to 20kHz / 20 000 Hz

Question 3

What is required to transmit sound waves

Answer 3

A medium is needed (e.g air, water)

Question 4

How to determine the speed of sound in air using a method involving a measurement of distance and time

Answer 4

1. Stand at a known, large distance from a solid wall
2. Make a noise (e.g a single clap)
3. Record the time from the noise to when the echo is heard
4. Use speed = distance / time, where distance = 2 x distance from the wall (as sound travelled there and back)

Question 5

How changes in amplitude and frequency affect the loudness and pitch of sound waves

Answer 5

• The higher the amplitude => The louder the sound
• The higher the frequency => The higher the pitch

Question 6

Definition of an echo

Answer 6

A reflection of a sound wave where the reflected sound arrives noticeably after the generated sound

Question 7

Definition of reverberation

Answer 7

A reflection of a sound wave where the reflected sound arrives almost at the same time as the generated sound

Question 8

Definition of ultrasound

Answer 8

Sound with a frequency higher than 20 kHz

Question 9

How sound is produced relate to its longitudinal nature ?

Answer 9

• All sound waves are produced by something vibrating.
• Vibrating sources cause the air around them to vibrate as a series of compressions and rarefactions.
• The compressions and rarefactions transfer energy through the medium.

Question 10

What are compressions ?

Answer 10

Regions of higher pressure due to particles being closer together

Question 11

What are rarefactions ?

Answer 11

Regions of lower pressure due to particles being spread further apart.

Question 12

Speed of sound in different mediums ?

Answer 12

• Fastest in solid as particles next to each other so energy can be transferred quickly.
• Slower in liquid than solid as particles are less tightly packed so slower sound propagation
• Slowest in gas as particles are far apart leads to inefficient energy transfer.