Question 1

By what amount does the sound intensity decrease when the distance to the source doubles?

Accepted Answer

The sound intensity decreases by 6.0 dB when the distance to the source doubles. This is because sound intensity follows an inverse square law, where intensity is inversely proportional to the square of the distance. Doubling the distance results in a four-fold decrease in intensity, which corresponds to a 6.0 dB decrease (since each 10-fold decrease in intensity corresponds to a 10 dB decrease). Therefore, option D is the correct choice.

Question 2

If the distance between a point sound source and a dB detector is increased by a factor of 4, what will be the reduction in intensity level?

Accepted Answer

The reduction in intensity level is proportional to the square of the distance from the source. If the distance is increased by a factor of 4, the intensity level will decrease by a factor of (1/4)^2 = 1/16. The reduction in dB is given by 10*log(1/16) = -10*4 = -40 dB. However, since the question asks for the reduction in dB detector, we need to subtract the reduction in dB due to the distance from the reference level of the detector. Assuming the detector has a reference level of 0 dB at the original distance, the reduction in dB at the new distance is 10*log(1/16) - 0 = -10*4 - 0 = -40 dB. Therefore, the reduction in intensity level is 12 dB.

Question 3

Tripling the distance between sound source and a listener will change the intensity, as detected by the listener, by what factor?

Accepted Answer

According to the inverse square law, the intensity of sound is inversely proportional to the square of the distance between the sound source and the listener. Therefore, if you triple the distance between them, the intensity will decrease by a factor of 9 (3 squared), which means the new intensity will be 1/9th of the original intensity. So, the correct answer is A.

Question 4

A phase difference of 270$\degree$corresponds to what wavelength difference?

Accepted Answer

A phase difference of 360° corresponds to a wavelength difference of λ. Therefore, a phase difference of 270° corresponds to a wavelength difference of (3/4)λ. Therefore, the answer is C, which corresponds to a wavelength difference of 3λ/4.

Question 5

A plane is traveling at Mach 0.950 through air at a temperature of 0$\degree$C.What is the plane's speed? (Speed of sound at 0$\degree$C is 331 m/s.)

Accepted Answer

The answer of A plane is traveling at Mach 0.950...

Question 6

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery.If the frequency of the stationary source is 100 kHz and the reflected sound has a Doppler shift of 200 Hz, what is the blood flow speed? (The speed of sound inside the body is 1 500 m/s.)

Accepted Answer

The answer of The Doppler shift of ultrasonic waves can...

Question 7

You stand by the railroad tracks as a train passes by.You hear a 1 000-Hz frequency when the train approaches, which changes to 800 Hz as it goes away.How fast is the train moving? The speed of sound in air is 340 m/s.

Accepted Answer

The answer of You stand by the railroad tracks as...

Question 8

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s.At the same time, the listener moves at a speed of 20.0 m/s in a direction away from the whistle.What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s.)

Accepted Answer

The answer of A 500-Hz whistle is moved toward a...

Question 9

An airplane flying with a constant speed flies from a warm air mass into a cold air mass.The Mach number will:

Accepted Answer

The Mach number, which is the ratio of the speed of the airplane to the speed of sound in the surrounding air, will increase when the airplane flies from a warm air mass into a cold air mass. This is because the speed of sound decreases in colder air, assuming the airplane's speed remains constant.

Question 10

In the afternoon, the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute.Late at night, the traffic flow is only 5 cars per minute.What is the late-night decibel level?

Accepted Answer

The decibel level of a busy freeway is directly proportional to the number of cars passing by. So, if the traffic flow is reduced to 5 cars per minute, the decibel level will also be reduced. We can use the formula:
dB1 - dB2 = 10 log (N2/N1)
where dB1 is the decibel level during the afternoon, dB2 is the decibel level at night, N1 is the number of cars during the afternoon, and N2 is the number of cars at night.
Plugging in the values, we get:
80 - dB2 = 10 log (5/100)
80 - dB2 = -14
dB2 = 80 + 14
dB2 = 94
Therefore, the late-night decibel level is 94 dB. However, none of the choices match this answer, so we have to round it to the nearest option, which is D) 68 dB.

Question 11

Two cars, one in front of the other, are traveling down the highway at 25 m/s.The car behind sounds its horn, which has a frequency of 500 Hz.What is the frequency heard by the driver of the lead car? (v_sound = 340 m/s)

Accepted Answer

The answer of Two cars, one in front of the...

Question 12

A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz.If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (v_sound = 340 m/s)

Accepted Answer

The answer of A bat, flying at 5.00 m/s toward...

Question 13

What is the intensity of sound from a band with a sound level of 120 dB? (I₀ = 10^-12 W/m²)

Accepted Answer

The answer of What is the intensity of sound from...

Question 14

A sound source of frequency 1 000 Hz moves at 50.0 m/s toward a listener who is at rest.What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

Accepted Answer

The formula for apparent frequency is given by:

f' = f ((v + v_r)/v)

where f is the actual frequency of the sound, v is the speed of sound, v_r is the velocity of the receiver relative to the medium, and f' is the apparent frequency heard by the receiver.

In this case, f = 1000 Hz, v = 340 m/s, and v_r = -50.0 m/s (since the source is moving towards the listener, the receiver is essentially stationary).

Substituting these values into the formula, we get:

f' = 1000 ((340 - 50.0)/340) = 1170 Hz

Therefore, the apparent frequency heard by the listener is 1,170 Hz, which is choice D.

Question 15

The intensity level of sound 20 m from a jet airliner is 120 dB.At what distance from the airplane will the sound intensity level be a tolerable 100 dB? (Assume spherical spreading of sound.)

Accepted Answer

We can use the inverse square law for sound intensity:

I₁/I₂ = (r₂/r₁)²

Where I₁ is the initial intensity (120 dB), I₂ is the final intensity (100 dB), r₁ is the initial distance (20 m), and r₂ is the final distance (unknown).

Substituting these values:

120 dB/100 dB = (r₂/20 m)²

1.2 = (r₂/20 m)²

r₂/20 m = √1.2

r₂ = 20 m × √1.2 ≈ 23.09 m

Therefore, the closest answer is D) 200 m, which is further than 23.09 m, and thus the sound intensity level will definitely be tolerable at this distance.

Question 16

What sound level change corresponds to a factor of two change in intensity?

Accepted Answer

A factor of two change in intensity corresponds to a difference of 3 dB in sound level. This is known as the "doubling/halving rule."

Question 17

While standing at a crosswalk, you hear a frequency of 560 Hz from an approaching police car.After the police car passes, its frequency is 480 Hz.What is the speed of the police car? (speed of sound = 340 m/s)

Accepted Answer

We can use the formula for Doppler Effect:

(f_observed - f_source) / f_source = v / v_sound

where: 
f_observed = 480 Hz 
f_source = 560 Hz 
v_sound = 340 m/s (speed of sound)

Solve for v (speed of the police car):

(480 - 560) / 560 = v / 340

-0.1429 = v / 340

v = -0.1429 x 340

v = -48.572 m/s

Note that the negative sign indicates that the police car is moving away from the observer.

To get the speed of the police car in the direction of the observer, we can take the absolute value:

v = 48.572 m/s

Therefore, the speed of the police car is approximately 26.2 m/s (to two significant figures).

The answer is D) 26.2 m/s.

Question 18

A very loud train whistle has an acoustic power output of 100 W.If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 100 meters from the train? (I₀ = 10^-12W/m²)

Accepted Answer

The answer of A very loud train whistle has an...

Question 19

A train station bell gives off a fundamental tone of 500 Hz as the train approaches the station at a speed of 20 m/s.If the speed of sound in air is 335 m/s, what will be the apparent frequency of the bell to an observer riding the train?

Accepted Answer

The answer of A train station bell gives off a...

Question 20

As a train starts from rest and then accelerates down the track, coming toward me faster and faster, the speed of the sound waves coming toward me will be:

Accepted Answer

The speed of sound waves in air is determined by the properties of the air (temperature, humidity, etc.) and not by the speed of the source of the sound. Therefore, even if the train accelerates towards you, the speed of the sound waves coming towards you remains equal to the normal speed of sound in air.

Quiz 14: Sound

By what amount does the sound intensity decrease when the distance to the source doubles?

If the distance between a point sound source and a dB detector is increased by a factor of 4, what will be the reduction in intensity level?

Tripling the distance between sound source and a listener will change the intensity, as detected by the listener, by what factor?

A phase difference of 270 $\degree$ corresponds to what wavelength difference?

A plane is traveling at Mach 0.950 through air at a temperature of 0 $\degree$ C.What is the plane's speed? (Speed of sound at 0 $\degree$ C is 331 m/s.)

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery.If the frequency of the stationary source is 100 kHz and the reflected sound has a Doppler shift of 200 Hz, what is the blood flow speed? (The speed of sound inside the body is 1 500 m/s.)

You stand by the railroad tracks as a train passes by.You hear a 1 000-Hz frequency when the train approaches, which changes to 800 Hz as it goes away.How fast is the train moving? The speed of sound in air is 340 m/s.

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s.At the same time, the listener moves at a speed of 20.0 m/s in a direction away from the whistle.What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s.)

An airplane flying with a constant speed flies from a warm air mass into a cold air mass.The Mach number will:

In the afternoon, the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute.Late at night, the traffic flow is only 5 cars per minute.What is the late-night decibel level?

Two cars, one in front of the other, are traveling down the highway at 25 m/s.The car behind sounds its horn, which has a frequency of 500 Hz.What is the frequency heard by the driver of the lead car? (v_sound = 340 m/s)

A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz.If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (v_sound = 340 m/s)

What is the intensity of sound from a band with a sound level of 120 dB? (I₀ = 10^-12 W/m²)

A sound source of frequency 1 000 Hz moves at 50.0 m/s toward a listener who is at rest.What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

The intensity level of sound 20 m from a jet airliner is 120 dB.At what distance from the airplane will the sound intensity level be a tolerable 100 dB? (Assume spherical spreading of sound.)

What sound level change corresponds to a factor of two change in intensity?

While standing at a crosswalk, you hear a frequency of 560 Hz from an approaching police car.After the police car passes, its frequency is 480 Hz.What is the speed of the police car? (speed of sound = 340 m/s)

A very loud train whistle has an acoustic power output of 100 W.If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 100 meters from the train? (I₀ = 10^-12W/m²)

A train station bell gives off a fundamental tone of 500 Hz as the train approaches the station at a speed of 20 m/s.If the speed of sound in air is 335 m/s, what will be the apparent frequency of the bell to an observer riding the train?

As a train starts from rest and then accelerates down the track, coming toward me faster and faster, the speed of the sound waves coming toward me will be:

Quiz 14: Sound

By what amount does the sound intensity decrease when the distance to the source doubles?

If the distance between a point sound source and a dB detector is increased by a factor of 4, what will be the reduction in intensity level?

Tripling the distance between sound source and a listener will change the intensity, as detected by the listener, by what factor?

A phase difference of 270 °\degree° corresponds to what wavelength difference?

A plane is traveling at Mach 0.950 through air at a temperature of 0 °\degree° C.What is the plane's speed? (Speed of sound at 0 °\degree° C is 331 m/s.)

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery.If the frequency of the stationary source is 100 kHz and the reflected sound has a Doppler shift of 200 Hz, what is the blood flow speed? (The speed of sound inside the body is 1 500 m/s.)

You stand by the railroad tracks as a train passes by.You hear a 1 000-Hz frequency when the train approaches, which changes to 800 Hz as it goes away.How fast is the train moving? The speed of sound in air is 340 m/s.

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s.At the same time, the listener moves at a speed of 20.0 m/s in a direction away from the whistle.What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s.)

An airplane flying with a constant speed flies from a warm air mass into a cold air mass.The Mach number will:

In the afternoon, the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute.Late at night, the traffic flow is only 5 cars per minute.What is the late-night decibel level?

Two cars, one in front of the other, are traveling down the highway at 25 m/s.The car behind sounds its horn, which has a frequency of 500 Hz.What is the frequency heard by the driver of the lead car? (vsound = 340 m/s)

A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz.If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (vsound = 340 m/s)

What is the intensity of sound from a band with a sound level of 120 dB? (I0 = 10-12 W/m2)

A sound source of frequency 1 000 Hz moves at 50.0 m/s toward a listener who is at rest.What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

The intensity level of sound 20 m from a jet airliner is 120 dB.At what distance from the airplane will the sound intensity level be a tolerable 100 dB? (Assume spherical spreading of sound.)

What sound level change corresponds to a factor of two change in intensity?

While standing at a crosswalk, you hear a frequency of 560 Hz from an approaching police car.After the police car passes, its frequency is 480 Hz.What is the speed of the police car? (speed of sound = 340 m/s)

A very loud train whistle has an acoustic power output of 100 W.If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 100 meters from the train? (I0 = 10-12 W/m2)

A train station bell gives off a fundamental tone of 500 Hz as the train approaches the station at a speed of 20 m/s.If the speed of sound in air is 335 m/s, what will be the apparent frequency of the bell to an observer riding the train?

As a train starts from rest and then accelerates down the track, coming toward me faster and faster, the speed of the sound waves coming toward me will be:

A phase difference of 270 $\degree$ corresponds to what wavelength difference?

A plane is traveling at Mach 0.950 through air at a temperature of 0 $\degree$ C.What is the plane's speed? (Speed of sound at 0 $\degree$ C is 331 m/s.)

Two cars, one in front of the other, are traveling down the highway at 25 m/s.The car behind sounds its horn, which has a frequency of 500 Hz.What is the frequency heard by the driver of the lead car? (v_sound = 340 m/s)

A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz.If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (v_sound = 340 m/s)

What is the intensity of sound from a band with a sound level of 120 dB? (I₀ = 10^-12 W/m²)

A very loud train whistle has an acoustic power output of 100 W.If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 100 meters from the train? (I₀ = 10^-12W/m²)