L1 - Properties Of Sound

Question 1

To hear sound you need ….

1….
2…

Answer 1

1. A source (vibration)
2. A medium (air,solid,liquid)

Question 2

What is the best medium for sound to travel through and why?

Answer 2

solid (tightly packed molecules/dense so they can transfer energy easily = efficient for sound transmission)

Question 3

Why are liquids and gases not the best medium for sound to travel?

Answer 3

liquid (closely linked, travels easily but lose energy over distance)
gas (molecules have lots of energy but further to travel)

Question 4

Why can sound not travel through a vacuum ?

Answer 4

Sound cannot travel through a vacuum as there are no particles present for vibrations to take place.

Question 5

What is the speed of sound (approx)

Answer 5

Approx. 340m/sec

Question 6

What factors can affect the speed at which sound will travel and why?

Answer 6

Density in atmosphere (more dense = quicker)
Heat in atmosphere (more kinetic energy)

Question 7

Define sound wave

Answer 7

A wave can be described as a disturbance that travels through a medium from one location to
another location.

Question 8

Sound wave is always made up of

Answer 8

Backwards and forward motion of particles, the particles moving forward will encounter particles moving back – densely packed.
causing a wave of positive and neg pressure.

Sound Wave is always made up of:
• Areas of positive pressure (particles moving closer) = compression
• Areas of negative pressure (particles moving further apart) = rarefaction

Question 9

Describe the tuning fork example

Answer 9

Strike tuning fork -→ fork vibrates back and forth -→back and forth displacement of vibrations, each particle will vibrate, then reaches detector (ear)

Question 10

2 types of wave motion

Answer 10

1. Transverse wave (water/ light) – wave is travelling perpendicular to source/particle
   (source/particle up and down, wave forwards/right)
2. Longitudinal wave (Sound) – wave is travelling parallel to source/particle – direction of wave is in the same direction to the movement of molecules (source/particle and wave both moving forwards and back)

Question 11

How to measure a wavelength and the units ?

Answer 11

peak -→ peak
• trough → trough
• any identical points
• In metres

Question 12

Peak of waves correspond to areas of_______ pressure (_______), and troughs correspond to areas of ______ pressure (_______) that’s why there are peaks and troughs on waves.

• Compression =
• Rarefaction =

Answer 12

Peak of waves correspond to areas of high pressure (compression), that’s why there are peaks and
troughs on waves.

• Compression = peak
• Rarefaction = trough

Question 13

Difference between periodic and aperiodic wave

Answer 13

Periodic wave: predictable, repeats itself. DIAGRAM

Aperiodic: Any sound that doesn’t repeat a basic pattern

Question 14

Difference between complex sound and pure tones

Answer 14

Complex sound: Sounds made up of two or more frequencies. The tone of the lowest
frequency is the “fundamental frequency”, the others are “overtones”. The overtones may
be whole number multiples of the fundamental frequency - in which case are called
harmonics.
• Pure tone: An audible tone that can be represented by a sine wave; Pure tones are only
of one frequency of vibratio

Question 15

What is a cycle and how is it measured? Include units

Answer 15

One complete vibration (rotation), made up of one area of compression (high pressure) and one area of rarefaction (low pressure).

Cycle = 1 compression + 1 rarefaction → Metres

To measure it is the line (distance from start of peak and end of trough) – in metres.

Question 16

What’s a period

Answer 16

Time it takes one cycle to occur

Question 17

What is frequency and how is it measured ? Include units

Answer 17

How many cycles occur per second.
Measured in Hertz

Question 18

• Longer wavelength = _______ frequency sound= __________ vibrations
• shorter wavelengths= _______higher frequency sound = ______ vibrations

Answer 18

• Longer wavelength = low frequency sound= fewer vibrations
• shorter wavelengths= higher frequency sound = more vibrations

Question 19

What is the frequency of a 6 cycle per second sound? Include units

Answer 19

6 Hz (hertz) per second

Question 20

Why can’t we measure pitch?

Answer 20

We can’t measure pitch as its subjective, it is the subjective sensation of frequecncy

Question 21

What is the human auditory field/dynamic range?

Answer 21

frequencies between 20Hz - 20,000Hz (20kHz)

Question 22

What frequencies are Infrasounds and Ultra sounds? Give examples of the animals that come in these ranges

Answer 22

Infrasound = Sounds below 20Hz (elephant, mole)
Ultrasound = all sounds above 20kHz (bat, dolphin)

Question 23

When older, hearing begins to decline from ______ frequencies

Answer 23

Higher

Question 24

What is amplitude and how is it measured? Include units

Answer 24

Amplitude is the distance from normal pressure to the point of maximum displacement
(equal to the height of the wave).

Measured in Decibels sound pressure level (dBSPL)

Further it deviates from normal atmospheric pressure, it is louder

Question 25

Why are peaks higher for louder sounds?

Answer 25

Increased force, particles move further creating larger compressions and rarefactions.

Further it deviates from normal atmospheric pressure, it is louder

Question 26

Is loudness objective or subjective?

Answer 26

Loudness is the subjective sensation of amplitude and cannot be measured

Question 27

Height of wave =

Length of wave =

Answer 27

Height of wave = amplitude/loudness

Length of wave = frequency/pitch

Question 28

What is sound diffraction, and what frequencies/wavelengths diffract best?

Answer 28

Diffraction – how sound bends.
• Shorter wavelengths/high pitch don’t travel or bend that well
• Longer wavelength / low pitch – diffract better bc can withstand movements

Question 29

Describe sound resonance?

Answer 29

Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration that matches its natural resonant frequency (Natural resonant frequency is the objects frequency at which it vibrates the most )

When this happens, the object or system absorbs energy from the external force and starts vibrating with a larger amplitude.

Question 30

Sound equations

Distance and time

Frequency and wavelength

Answer 30

D top then V T

V top then F W