sound waves
are produced by the vibrations of matter
Sound
can be produced by vibrating strings (such as in a piano, a violin, or a guitar), the oscillating diaphragm of a stereo speaker, or the vibration of your vocal cords
compressions
Regions of the medium having high density and pressure
rarefactions
regions of low density and pressure
sound
is a pressure wave and a longitudinal wave
speed of sound
sound travels faster in a ______ than one with higher density
fluid with lower density
For an ideal gas, the ratio_______ depends on the gas temperature, so the speed of sound depends on temperature
B/ρ
At other air temperatures TC (measured in Celsius), the speed of sound is given by
Intensity I
is defined as the average power Pav per unit area A perpendicular to the direction of propagation:
Formula of Intensity is
the intensity of a point source decreases as the distance r from the source increases
The intensity range of human hearing spans ____ orders of magnitude
12
sound level in terms of base 10 logarithms is
Sound level is measured in decibels (dB), although the quantity defined is actually dimensionless. The threshold of human hearing is ____ dB and sound is painful at _____ dB.
0 , 120
Sound waves are divided into three categories:
: (1) Audible waves lie within the range of sensitivity of the human ear (from 20 Hz to 20,000 Hz)
(2) Infrasonic waves have frequencies below the audible range (f < 20 Hz)
(3) Ultrasonic waves have frequencies above the audible range (f > 20,000 Hz)
Doppler Effect
indicates the change in frequency due to relative motion between the wave source and the observer
For sound waves, the observed frequency is (formula)
When the observer moves toward the source
a positive (+) speed is substituted for vO
When the observer moves away from the source
a negative (–) speed is substituted for vO
When the source moves toward the observer
a positive (+) speed is substituted for vS
When the source moves away from the observer
a negative (–) speed is substituted for vS
Superposition Principle, superimposing
When two (or more) waves travel in the same medium, the resulting wave function is found by __________ (adding) the individual wave functions.
in Superposition Principle, The resultant wave is the __________ of the individual waves
superposition
Interference, interfere
When two waves exist in the same medium, they don’t collide; they _______ with each other
When the resulting pulse’s height is greater than that of both original waves, the result is __________
constructive interference
When the resulting pulse’s height is smaller than that of each original wave, the result is _________
destructive interference
. If the two pulses have the same amplitude but one is inverted with respect to the other, the resulting wave profile is __________
momentarily flat
When you shout into a gorge or at a large wall, you hear your voice echo because when a wave travels to the end of a medium—in this case, the air—the wave is
reflected back into the medium
resonance
If a periodic force is applied to a system, the amplitude of the resulting motion is greatest when the frequency of the applied force is equal to one of the natural frequencies of the system
The profile of a wave reflected from a fixed end is
inverted
The profile of a wave reflected from a free end is
upright
resonance frequencies
Because an oscillating system exhibits a large amplitude when driven at any of its natural frequencies, these frequencies are often referred to as
beating
_____ is the periodic variation in intensity at a given point due to the superposition of two waves having slightly different frequencies
beat frequency (formula)
Light and other forms of radiation are _________ in the form of waves that propagate according to the laws of electricity and magnetism
electromagnetic disturbances
The behavior of these _______ has clear similarities with mechanical waves. However, electromagnetic waves do not require a medium; they can propagate through empty space
electromagnetic waves
frequency and wavelength of any electromagnetic wave in a vacuum are given by
c = fλ
electromagnetic spectrum
refers to the continuum of electromagnetic waves arranged in order by frequency (and wavelength)
electromagnetic waves do not need a medium, the Doppler effect for EM waves is simply a
relative-velocity phenomenon
If the source emits EM waves that have a frequency fS, the observed frequency fO is given by
When a light source moves away from an observer, the wavelength is longer and the light looks redder
redshift
When a light source moves toward the observer, the wavelength is shorter and the light looks bluer
a blueshift
Radar and sonar
____ and ______ are sensor systems that use the propagation of waves to detect and localize targets
echo
_____ is the reflection of sound waves off of some distant object
echolocation
When bats, dolphins and other animals use sonar naturally, usually to find prey
Sound Navigation and Ranging
is a system for the detection of objects and for measuring the depth of water. It works by emitting sound pulses and measuring how long it takes the echoes to return.
Radio Detection and Ranging
is a system for calculating the position, distance or other important characteristic of a distant object
Detection (or navigation)
refers to locating objects
in ______ a transmitter with an oscillator is used to generate radio waves, and a waveguide links the transmitter to the antenna
radar
in _______ a electrical energy is supplied directly to a hydrophone array which converts it to sound waves
a sonar
_____ the received signals normally go through a low noise amplifier before being down-converted to an intermediate frequency
radar
the received signals for ______ go through a pre-amplifier to shape the signal (front-end conditioning) prior to being sent to the signal processing unit
a sonar
Three distinct types of radar systems are
[1] the static early warning area surveillance platform, [2] the targeting and fire control platform, and [3] the battlefield reconnaissance detection and search platform
Active radar
a type of radar at which a radio wave is emitted from an antenna and reflects off objects the wave encounters
passive radar
system relies on a signal transmitted from a different location. This type of radar system is called bistatic.
Active sonar
is emitting pulses of sound and listening to echoes.
Passive sonar
is essentially listening for the sound or “noise” made by marine objects (such as submarines or ships) and marine animals (such as whales)
Radar and sonar are capable of distance measurement through the timing method
Range R = vt/2
Radar and sonar are also capable of measuring the speed of the target in the following ways:
[1] Measuring distance and recording where the target was located a set time ago;
[2] Analyzing the Doppler signal where the target’s motion relative to the transmitter and receiver produces a change in frequency.
Passive sonar systems
able to determine the range and bearing of an acoustic target without giving away the location of its source