Sound Flashcards
Attenuation of a wave refers to a decrease in…
intensity
The perceived frequency of a wave is expected to be greater than the actual frequency when the source is... Moving away from observer Moving towards observer Moving at the same velocity Standing Still
Moving towards observer
Doppler Equation
f’ = f0 (vsound - vobserver / vsound + vsource)
After dropping off its passengers, a taxi leaves at a velocity of 30 m/s. The engine emits a sound wave at a frequency of 100 Hz. What approximate frequency do the passengers hear? Use 340 m/s as the speed of sound.
Vsource is positive because the taxi engine is moving away from the passengers. The passengers are stationary so vobserver is 0. The emitted frequency and speed of sound is given in the question stem. Plugging in the variables into the Doppler equation results in:
f’ = f0 (vsound - vobserver / vsound + vsource)
f’ = 100 Hz (340 m/s - 0 m/s / 340 m/s + 30 m/s)
f’ = 100 Hz (340 m/s / 370 m/s)
f’ = 92 Hz
A technician is measuring a patient’s blood flow with a stationary ultrasound transducer. The technician notices that the received frequency by the transducer is less than the emitted frequency. What direction is the blood moving relative to the transducer?
A transducer emits a wave and measures the frequency of the reflected wave. If the received frequency is less than the emitted frequency, then the blood must be traveling away from the transducer. As blood is moving away from the transducer, the reflected ultrasound waves become more spread out, resulting in a lower frequency.
Why does sound travel faster in liquid?
The liquid is less compressible than gas, so sound waves do not have to compress the liquid molecules as much before being transmitted through the medium.
Robert is driving towards a church that is ringing bells. Robert is driving at a pace of 35 m/s. The bells are ringing at 2.8 kHz. Assuming the speed of sound in air is 340 m/s, he perceives the frequency of the bells as…
The vobserver is positive because the observer is moving towards the source. The source is stationary, so vsource can be excluded from our equation:
f’ = f0 (vsound + vobserver / vsound )
f’ = 2,800 Hz (340 m/s + 35 m/s / 340 m/s)
f’ = 2,800 Hz (375 m/s / 340 m/s)
f’ = 3,100 Hz
What does the speed of sound depend on?
The media it travels through, not the wave itself
What is the equation for velocity of sound?
v=sqrt(B/rho) B is bulk modulus and rho is density
What is the range of sound for humans?
20-20,000 Hz
True or False: Sound waves are longitudinal, compression, and pressure waves
True
What is the decibel scale equation?
dB=10log(I/Io)
What is intensity measured in?
It tends to be measured in decibels which comes down to Watts/m2
True or False: Intensity is proportional to amplitude
true
v=sqrt(B/rho) B is bulk modulus and rho is density
True or False: Speed of sound is directly proportional to bulk modulus
TRUE
