Chapter 14 Flashcards
(21 cards)
What are sound waves?
Their 3 categories?
Longitudinal waves travelling through a medium
They are a series of compressions (higher density and pressure) and rarefactions (power density and pressure)
Audible waves - in range of human hearing (20-20000Hz)
Infrasonic Waves- lower than 20Hz can cause adverse health effects
Ultrasonic Waves- frequencies higher than 20000Hz, used for medical diagnostics and treatments
Audible and ultrasonic can be used for echolocation
Slide 35-36 Jan 24
How is the speed of sound calculated?
In general
In air
And in a longitudinal wave along a solid thin rod
V= square root Bulk modulus/ density
Use the temperature equation for speed of sound in air
v= square root Y/ρ in a solid thin rod
V=343 m/s
What is the intensity of a sound wave?
How does a 10dB increase affect intensity?
The rate at which energy flows from the source through the surface divided by the area of the surface
I= power/area
10dB increase, increases intensity by a factor of 10
What is the threshold of pain in decibels?
120 dB
90dB is where earplugs are recommended
This is 1000x increase in intensity
What are spherical waves?
Device emitting sound waves in all directions (small round speaker)
Wave moves uniform
Power of wave is distributed uniformly over surface area of sphere
How do you compare two intensities with two different radii?
I2/I1 = r1^2 / r2^2
What is the Doppler effect?
What are the variables?
When a wave source and observer are in relative motion, the observed frequency is different than the frequency of the wave produced by the source
Observer = o Source = s
What is the equation using frequency of the source, speed of sound, and speed of observer to find frequency of observer?
What about using speed of source?
What is Vo when the observer is moving away from source? To the source?
fo=fs(v+vo / v)
fo=fs(v / v-vs)
When observer is moving towards the source, Vo= positive
Moving away from source, Vo=negative
V=343 m/s
If observer A is closer to source than observer B, who hears higher frequency?
Observer B hears higher frequency since the wavelengths are shorter closer to the source
Slide 11 Jan 31
What are shock waves?
If a source is moving faster than the wave speed, then wave crests form shock waves
This is a sonic boom
Slide 18 Jan 31
How does interference effect sound waves?
Slide 22 Jan 31
Want path lengths to be equal
Slide 24-25 Jan 31
What is the distance between consecutive nodes on a standing wave?
What is h distance between consecutive antinodes?
The wave length
Half the wavelength
What stays constant in a standing wave?
How do you find length of a string in a standing wave?
The frequency since all points are in simple harmonic motion
Nodes never move
Antinodes don’t either
L=n(1/2 λ)
n=number of harmonics
Slide 10 Feb 5
What are resonant or natural frequencies?
What’s the equation for natural frequencies?
Since only certain wavelengths can exist means only certain frequencies can exist
fn=n(v/2L)=n/2L (square root F/μ)
μ=m/L
How are damping forces over come in standing waves?
Using an external driving force to keep the energy of an oscillating system constant
How are standing waves in narrow pipes with two open ends measured?
Slide 22 Feb 5
First harmonic= λ1=2L, f1=v/λ1=v/2L
Second harmonic= λ2=L, f2=v/L=2f1
Third harmonic= λ3=2/3L, f3=3v/2L=3f1
How are standing waves in a narrow pipe open at one end and closed at the other measured?
Slide 24 Feb 5
first harmonic- λ1=4L, f1=v/λ1=v/4L
Third harmonic- λ3=4/3 L, f3=3v/4L=3f1
Fifth harmonic- λ5=4/5 L, f5= 5v/4L=5f1
Only resonates at off number frequencies
What are Beats?
Pulsation caused by two waves in close frequency and the superposition of the two waves produces a wave whose amplitude varies periodically
Waves at some fixed location are periodically in and out of phase
Slide 29 Feb 5
What is the time for when two waves are in phase then go through a number of oscillations are are in phase again?
Tbeat- period beat
|f2Tbeat-f1Tbeat|=1
|f2-f1|=fbeat
What is timbre?
Most instruments produce complex sound waves that are the superposition of a fundamental frequency and its harmonics
Different instruments can be identified because they produce harmonics of different relative amplitudes
The sounds of different instruments differ in timbre
Slide 8-9 Feb 7
How is the outer ear, middle ear, and inner ear broken down?
Outer ear: pinna, ear canal, ear drum (tympanum)
Middle ear: the auditory ossicles (hammer, anvil, stirrup)
Inner ear: the cochlea
Slide 11 Feb 7
