Chapter 7: Waves and Sound

Question 1

crest

Answer 1

distance from one maximun of the wave

Question 2

wavelenght (λ)

Answer 2

diatance form one crest to the other

Question 2

frequency (f)

Answer 2

number of wavelenghts passing a fixed point per second, measure in heartz (Hz)

Question 3

propagation speed (v)

Answer 3

v = f λ

f = frequency
λ = wavelenght

Question 4

angular frequency (w)

Answer 4

w = 2 π f = 2π / T

f = frequency
T = period

Question 4

perios (T)

Answer 4

T = 1 / f

unit is second

Question 5

amplitude (A)

Answer 5

maximun magnitude of displacement in a wave

Question 5

phases in waves

Answer 5

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.

Question 6

traveling wave

Answer 6

wave is moving

Question 7

standinf waves

Answer 7

the only movement is amplitudeat fixed points along the lenght of the string

Question 8

speed of sound is

Answer 8

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.

Question 9

the speed of sound in air at 20C is ____

Answer 9

343 m/s

Question 10

normal range for a human hearing is

Answer 10

20 Hz to 20,000Hz

Infrasonic is below 20 Hz

Ultrasonic is above 20,000 Hz

Question 10

doppler effect

Answer 10

f’ =f ( v ± vd ) / (v (reverse of (±)) vs)

vd = speed of the detector
vs = speed of the source

Question 11

doppler effect explained

Answer 11

if the source and detector are moving towards each other the perceived frequency f’ is greater than the actual frequency f

Question 12

intensity is inversely proportional to the square of the ____

Answer 12

distance from the source

I ∝ 1 / r^2

Question 12

sound that a human can hear that causes pain intensity:

Answer 12

10 W / m^2

Question 13

intensity

Answer 13

I = P / A

P = power
A = area

unit is W / m^2

Question 14

softest sound that a human can hear

Answer 14

1 x 10^ -12 W / m^2

Question 15

perforation fo the eardrum

Answer 15

1 x 10^4 W / m^2

Question 16

sound lebel

Answer 16

β = 10 log I / Io

β = sound level
I =intensity of the sound wave
Io= threshold of hearing (10^-12 W/m^2)

Question 16

strings

Answer 16

λ = 2L / n

L = lenght of the string
n = it is called the harmonic

Question 16

when intensity of sound is changed by some factor, we can calculate the new sound using:

Answer 16

βf = βi + 10 If / Ii

If / Ii ratio is the final intensity over the initial intensity

Question 17

first harmonic in string

Answer 17

λ = 2L

L = λ /2

Question 18

third harmonic in string

Answer 18

λ = 2L / 3

L = 3λ / 2

Question 19

second harmonic in string

Answer 19

λ = L

Question 20

rule for harmonic in string

Answer 20

the number of antinodes present will tell you which harmonic it is

Question 21

open pipes rule

Answer 21

the number os nodes present will tell you which harmonic it is

Question 22

second harmonic in open pipes

Answer 22

L = λ

Question 23

first harmonic in open pipes

Answer 23

L = λ / 2

Question 24

third harmonic in open pipes

Answer 24

L = 3λ / 2

Question 24

closed pipes rule

Answer 24

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

Question 25

third harmonic in closed pipes

Answer 25

L = 3λ / 4

Question 25

first harmonic in closed pipes

Answer 25

L = λ / 4

Question 26

fifth harmonic in closed pipes

Answer 26

L = 5λ / 4