Chapter 7: Waves and Sound Flashcards
crest
distance from one maximun of the wave
wavelenght (λ)
diatance form one crest to the other
frequency (f)
number of wavelenghts passing a fixed point per second, measure in heartz (Hz)
propagation speed (v)
v = f λ
f = frequency
λ = wavelenght
angular frequency (w)
w = 2 π f = 2π / T
f = frequency
T = period
perios (T)
T = 1 / f
unit is second
amplitude (A)
maximun magnitude of displacement in a wave
phases in waves
if two waves are perfectly in phase, the resultant wave has an amplitude equal to the sum of the amplitude of the ywo waves. If two equal waves are exactly 180 degrees out of phase, then the resultant wave has zero amplitude.
traveling wave
wave is moving
standinf waves
the only movement is amplitudeat fixed points along the lenght of the string
speed of sound is
v = √B / ρ
B= bulk modulud, a measure of the medium resistance to compression (B increases from gas to solid)
ρ = density of the medium
the speed of sound is fastest in a solid with low density and slowest in a very dense gas.
the speed of sound in air at 20C is ____
343 m/s
normal range for a human hearing is
20 Hz to 20,000Hz
Infrasonic is below 20 Hz
Ultrasonic is above 20,000 Hz
doppler effect
f’ =f ( v ± vd ) / (v (reverse of (±)) vs)
vd = speed of the detector
vs = speed of the source
doppler effect explained
if the source and detector are moving towards each other the perceived frequency f’ is greater than the actual frequency f
intensity is inversely proportional to the square of the ____
distance from the source
I ∝ 1 / r^2
sound that a human can hear that causes pain intensity:
10 W / m^2
intensity
I = P / A
P = power
A = area
unit is W / m^2
softest sound that a human can hear
1 x 10^ -12 W / m^2
perforation fo the eardrum
1 x 10^4 W / m^2
sound lebel
β = 10 log I / Io
β = sound level
I =intensity of the sound wave
Io= threshold of hearing (10^-12 W/m^2)
strings
λ = 2L / n
L = lenght of the string
n = it is called the harmonic
when intensity of sound is changed by some factor, we can calculate the new sound using:
βf = βi + 10 If / Ii
If / Ii ratio is the final intensity over the initial intensity
first harmonic in string
λ = 2L
L = λ /2
third harmonic in string
λ = 2L / 3
L = 3λ / 2
second harmonic in string
λ = L
rule for harmonic in string
the number of antinodes present will tell you which harmonic it is
open pipes rule
the number os nodes present will tell you which harmonic it is
second harmonic in open pipes
L = λ
first harmonic in open pipes
L = λ / 2
third harmonic in open pipes
L = 3λ / 2
closed pipes rule
count the number of quarter-wavelenght contained in the pipe to determine the harmonic. there are only odd harmonics
λ = 4L / n
f = n v / 4 L
third harmonic in closed pipes
L = 3λ / 4
first harmonic in closed pipes
L = λ / 4
fifth harmonic in closed pipes
L = 5λ / 4
