Sound

Question 1

Do sound waves travel longitudinally or transversely?

Answer 1

Longitudinal

Question 2

To increase the intensity level by +10dB, the intensity must be increased by how much?

Answer 2

by a factor of 10!

10 = 10 log (x*I/I0) 
1 = log (x)
10^1 = x = 10

Question 3

What is the difference between traveling and standing waves?

Answer 3

Traveling waves are those waves where the wave pattern moves through the medium. Standing waves are formed by the interference of two traveling waves, traveling in opposite directions, usually because of boundary conditions.

Question 4

Does speed of sound increase or decrease with increasing temperature?

Answer 4

Increase

Question 5

Does speed of sound increase or decrease with a denser medium?

Answer 5

Increase

Question 6

Intensity of sound increases with?

Answer 6

Increasing density, so intensity of sound in water is greater than in air

Question 7

Do sound waves with higher or lower frequency have the greatest velocity?

Answer 7

Trick question! Sounds waves of all frequencies move at the same speed in a given medium. So unless you change the medium, the speed with be the same for each frequency.

Question 8

How is intensity related to distance away from sound source?

Answer 8

The intensity of a sound wave decreases as the inverse square of its distance from the source. Looking at the equation I = P/A = P/4pi*r^2.

As radius increases by 3, intensity will decrease by a factor of 9.

Question 9

If a phonon has 1 J of energy with a frequency of 100Hz, what other energy can be observed from this sound wave?

Answer 9

Any whole number multiple of 1 J . So 1.5 J would not be possible.

Question 10

What are some things ultrasound can see? Like in medical imaging?

Answer 10

Bone in flesh.
Gas-filled stomach and stomach wall.
Gallstones in gallbladder.

NOT bladder wall and urine in bladder because density of bladder wall too close to flesh and density of urine too close to water, so sound won’t reflect much since the two mediums are so similar.

Question 11

What is the smallest object an ultrasonic imager can see?

Answer 11

Ultrasonic waves do not allow you to see objects that are smaller than the wavelength of the sound,

Question 12

When calculating how long it takes for a sound source to hear the sound it emitted, DON’T FORGET TO 2*DISTANCE BECAUSE YOU HAVE TO TRAVEL AWAY AND BACK!!!

Answer 12

Don’t forget!

Question 13

What is the relationship between intensity and distance from sound source?

Answer 13

I = 1/r^2

Question 14

For every drop in intensity of a factor of 10, how much does the decibel decrease?

Answer 14

10 dB

Question 15

For every drop in 10 dB, how much does the intensity decrease?

Answer 15

By a factor of 10

Question 16

When wave travels from one medium to another, how does this affect the frequency?

Answer 16

Frequency does not change, it only changes when the sender or receiver is moving relative to one another.

Question 17

How is wave speed affected by moving objects?

Answer 17

It is not affected by moving objects, you have mistaken this effect with frequency. Wave speed is affected by change in medium and temperature fluctuations.

Question 18

If two cars are traveling at the same speed in the same direction and emitting the same frequency sound, what beat frequency do they hear?

Answer 18

There will be no beats because relative speed is 0 and each car will hear the same frequency emitted.

Question 19

How are frequency and length of a pipe related?

Answer 19

f = 1/L

Question 20

How does wave reflection work?

Answer 20

There is an interface between two media that propagate sound at different speeds, and the some of it gets reflected back at that interface

Question 21

If the intensity of sound increased by a factor of 2, how much does dB increase by?

Answer 21

+ 3 dB because

dB = 10log(2) = 3

Question 22

Can radars travel in a vacuum?

Answer 22

Yes! They are EM waves so they can travel through a vacuum unlike sound waves. Also, radar are radio waves so they are transverse waves, not longitudinal waves like sound waves.

Question 23

Why is it harder to detect small objects using a radar?

Answer 23

Because the wavelength may be too long compared to the object to be reflected by the object.

Question 24

What is the beat frequency between any two harmonics?

Answer 24

A harmonic as well

Question 25

What is the ratio of the fundamental frequency of an open pipe to a closed pipe?

Answer 25

2:1

because the wavelengths are in a ratio of 2L:4L and frequency is reciprocal

Question 26

To increase the speed of sound, should it travel through air with heavy or light molecules?

Answer 26

Lighter molecules

Question 27

Why does your voice get higher when you suck in helium and talk?

Answer 27

Helium is lighter than the molecules in air like N2, so speed of sound is faster and since frequency is proportional to speed, you get a higher pitch

Question 28

What is the relation between speed of sound and temperature?

Answer 28

3/2RT = 1/2mv^2

Question 29

Is the wave speed on a string and in a pipe the same?

Answer 29

No, the wave speed for pipes is the speed of sound, but the wave speed for strings depend on tension and density of string.

Question 30

Is wave speed on a string affected by temperature changes?

Answer 30

Nope, it’s pipes that are affected.

Question 31

Can waves be produced on strings in a vacuum?

Answer 31

Yes, because the string would be the medium, but you probably wouldn’t be able to hear it because the wave normally causes the air to vibrate and then we hear it but since there is no air you wouldn’t hear it.